CVE-2021-21299

hyper is an open-source HTTP library for Rust (crates.io). In hyper from version 0.12.0 and before versions 0.13.10 and 0.14.3 there is a vulnerability that can enable a request smuggling attack. The HTTP server code had a flaw that incorrectly understands some requests with multiple transfer-encoding headers to have a chunked payload, when it should have been rejected as illegal. This combined with an upstream HTTP proxy that understands the request payload boundary differently can result in "request smuggling" or "desync attacks". To determine if vulnerable, all these things must be true: 1) Using hyper as an HTTP server (the client is not affected), 2) Using HTTP/1.1 (HTTP/2 does not use transfer-encoding), 3) Using a vulnerable HTTP proxy upstream to hyper. If an upstream proxy correctly rejects the illegal transfer-encoding headers, the desync attack cannot succeed. If there is no proxy upstream of hyper, hyper cannot start the desync attack, as the client will repair the headers before forwarding. This is fixed in versions 0.14.3 and 0.13.10. As a workaround one can take the following options: 1) Reject requests that contain a `transfer-encoding` header, 2) Ensure any upstream proxy handles `transfer-encoding` correctly.

hyper is an open-source HTTP library for Rust (crates.io). In hyper from version 0.12.0 and before versions 0.13.10 and 0.14.3 there is a vulnerability that can enable a request smuggling attack. The HTTP server code had a flaw that incorrectly understands some requests with multiple transfer-encoding headers to have a chunked payload, when it should have been rejected as illegal. This combined with an upstream HTTP proxy that understands the request payload boundary differently can result in "request smuggling" or "desync attacks". To determine if vulnerable, all these things must be true: 1) Using hyper as an HTTP server (the client is not affected), 2) Using HTTP/1.1 (HTTP/2 does not use transfer-encoding), 3) Using a vulnerable HTTP proxy upstream to hyper. If an upstream proxy correctly rejects the illegal transfer-encoding headers, the desync attack cannot succeed. If there is no proxy upstream of hyper, hyper cannot start the desync attack, as the client will repair the headers before forwarding. This is fixed in versions 0.14.3 and 0.13.10. As a workaround one can take the following options: 1) Reject requests that contain a `transfer-encoding` header, 2) Ensure any upstream proxy handles `transfer-encoding` correctly.

hyper's HTTP server code had a flaw that incorrectly understands some requests with multiple transfer-encoding headers to have a chunked payload, when it should have been rejected as illegal. This combined with an upstream HTTP proxy that understands the request payload boundary differently can result in "request smuggling" or "desync attacks".

### Summary hyper's HTTP server code had a flaw that incorrectly understands some requests with multiple transfer-encoding headers to have a chunked payload, when it should have been rejected as illegal. This combined with an upstream HTTP proxy that understands the request payload boundary differently can result in "request smuggling" or "desync attacks". ### Vulnerability The flaw was introduced in https://github.com/hyperium/hyper/commit/26417fc24a7d05df538e0f39239b373c5c3d61f6, released in v0.12.0. Consider this example request: ``` POST /yolo HTTP/1.1 Transfer-Encoding: chunked Transfer-Encoding: cow ``` This request *should* be rejected, according to RFC 7230, since it has a `Transfer-Encoding` header, but after folding, it does not end in `chunked`. hyper would notice the `chunked` in the first line, and then check the second line, and thanks to a missing boolean assignment, *not* set the error condition. hyper would treat the payload as being `chunked`. By differing from the spec, it is possible to send requests like these to endpoints that have different HTTP implementations, with different interpretations of the payload semantics, and cause "desync attacks". There are several parts of the spec that must also be checked, and hyper correctly handles all of those. Additionally, hyper's *client* does not allow sending requests with improper headers, so the misunderstanding cannot be propagated further. Read more about desync attacks: https://portswigger.net/research/http-desync-attacks-request-smuggling-reborn ### Impact To determine if vulnerable, all these things must be true: - **Using hyper as an HTTP *server*.** The client is not affected. - **Using HTTP/1.1.** HTTP/2 does not use `transfer-encoding`. - **Using a vulnerable HTTP proxy upstream to hyper.** If an upstream proxy correctly rejects the illegal transfer-encoding headers, the desync attack cannot succeed. If there is *no* proxy upstream of hyper, hyper cannot *start* the desync attack, as the client will repair the headers before forwarding. ### Patches We have released and backported the following patch versions: - v0.14.3 - v0.13.10 ### Workarounds Besides upgrading hyper, you can take the following options: - Reject requests that contain a `transfer-encoding` header. - Ensure any upstream proxy handles `transfer-encoding` correctly. ### Credits This issue was initially reported by ZeddYu Lu From Qi An Xin Technology Research Institute.

hyper es una biblioteca HTTP de código abierto para Rust (crates.io). En Hyper desde la versión 0.12.0 y antes de las versiones 0.13.10 y 0.14.3, se presenta una vulnerabilidad que puede habilitar un ataque de trafico no autorizado de peticiones. El código del servidor HTTP tenía un fallo que entiende incorrectamente que algunas peticiones con múltiples encabezados transfer-encoding tienen una carga útil fragmentada, cuando debería haber sido rechazada como ilegal. Esto, combinado con un proxy HTTP aguas arriba que entiende el límite de carga útil de la petición de manera diferente, puede resultar en "request smuggling" o "desync attacks". Para determinar si es vulnerable, todas estas cosas deben ser ciertas: 1) Usar Hyper como servidor HTTP (el cliente no se ve afectado), 2) Usar HTTP/1.1 (HTTP/2 no usa transfer-encoding), 3) Usar un Proxy HTTP vulnerable aguas arriba de hiper. Si un proxy aguas arriba rechaza correctamente los encabezados transfer-encoding ilegales, el ataque de desincronización no puede tener éxito. Si no existe un proxy aguas arriba de Hyper, Hyper no puede iniciar el ataque de desincronización, ya que el cliente reparará los encabezados antes de reenviar. Esto se corrige en las versiones 0.14.3 y 0.13.10. Como solución alternativa, se pueden tomar las siguientes opciones: 1) Rechazar las peticiones que contengan un encabezado "transfer-encoding", 2) Asegurarse de que cualquier proxy ascendente maneje correctamente "transfer-encoding"