CVE-2023-6245

The Candid library causes a Denial of Service while parsing a specially crafted payload with 'empty' data type. For example, if the payload is `record { * ; empty }` and the canister interface expects `record { * }` then the Rust candid decoder treats empty as an extra field required by the type. The problem with the type empty is that the candid Rust library wrongly categorizes empty as a recoverable error when skipping the field and thus causing an infinite decoding loop. Canisters using affected versions of candid are exposed to denial of service by causing the decoding to run indefinitely until the canister traps due to reaching maximum instruction limit per execution round. Repeated exposure to the payload will result in degraded performance of the canister. Note: Canisters written in Motoko are unaffected.

The Candid library causes a Denial of Service while parsing a specially crafted payload with 'empty' data type. For example, if the payload is `record { * ; empty }` and the canister interface expects `record { * }` then the Rust candid decoder treats empty as an extra field required by the type. The problem with the type empty is that the candid Rust library wrongly categorizes empty as a recoverable error when skipping the field and thus causing an infinite decoding loop. Canisters using affected versions of candid are exposed to denial of service by causing the decoding to run indefinitely until the canister traps due to reaching maximum instruction limit per execution round. Repeated exposure to the payload will result in degraded performance of the canister. Note: Canisters written in Motoko are unaffected.

The Candid library causes a Denial of Service while parsing a specially crafted payload with `empty` data type. For example, if the payload is `record { * ; empty }` and the canister interface expects `record { * }` then the rust candid decoder treats `empty` as an extra field required by the type. The problem with type `empty` is that the candid rust library wrongly categorizes `empty` as a recoverable error when skipping the field and thus causing an infinite decoding loop. Canisters using affected versions of candid are exposed to denial of service by causing the decoding to run indefinitely until the canister traps due to reaching maximum instruction limit per execution round. Repeated exposure to the payload will result in degraded performance of the canister. For asset canister users, `dfx` versions `>= 0.14.4` to `<= 0.15.2-beta.0` ships asset canister with an affected version of candid. ### Unaffected - Rust canisters using candid `< 0.9.0` or `>= 0.9.10` - Rust canister interfaces of type other than `record { * }` - Motoko based canisters - dfx (for asset canister) `<= 0.14.3` or `>= 0.15.2` ### References - [GitHub Security Advisory (GHSA-7787-p7x6-fq3j)](https://github.com/dfinity/candid/security/advisories/GHSA-7787-p7x6-fq3j) - [dfinity/candid/pull/478](https://github.com/dfinity/candid/pull/478) - [Candid Library Reference](https://internetcomputer.org/docs/current/references/candid-ref) - [Candid Specification](https://github.com/dfinity/candid/blob/master/spec/Candid.md) - [Internet Computer Specification](https://internetcomputer.org/docs/current/references/ic-interface-spec)

### Impact The Candid library causes a Denial of Service while parsing a specially crafted payload with `empty` data type. For example, if the payload is `record { * ; empty }` and the canister interface expects `record { * }` then the rust candid decoder treats `empty` as an extra field required by the type. The problem with type `empty` is that the candid rust library wrongly categorizes `empty` as a recoverable error when skipping the field and thus causing an infinite decoding loop. Canisters using affected versions of candid are exposed to denial of service by causing the decoding to run indefinitely until the canister traps due to reaching maximum instruction limit per execution round. Repeated exposure to the payload will result in degraded performance of the canister. For asset canister users, `dfx` versions `>= 0.14.4` to `<= 0.15.2-beta.0` ships asset canister with an affected version of candid. #### Unaffected - Rust canisters using candid `< 0.9.0` or `>= 0.9.10` - Rust canister interfaces of type other than `record { * }` - Motoko based canisters - dfx (for asset canister) `<= 0.14.3` or `>= 0.15.2` ### Patches The issue has been patched in `0.9.10`. All rust based canisters on candid versions `>= 0.9.0` must upgrade their candid versions to `>= 0.9.10` and deploy their canisters to mainnet as soon as possible. ### Workarounds There is no workaround for canisters using the affected versions of candid other than upgrading to patched version. ### References - [dfinity/candid/pull/478](https://github.com/dfinity/candid/pull/478) - [Candid Library Reference](https://internetcomputer.org/docs/current/references/candid-ref) - [Candid Specification](https://github.com/dfinity/candid/blob/master/spec/Candid.md) - [Internet Computer Specification](https://internetcomputer.org/docs/current/references/ic-interface-spec)

La librería Candid provoca una denegación de servicio mientras analiza un payload especialmente manipulado con un tipo de datos "vacío". Por ejemplo, si el payload es `record { * ; empty }` y la interfaz del recipiente espera `record { * }`, entonces el decodificador sincero de Rust trata el vacío como un campo adicional requerido por el tipo. El problema con el tipo vacío es que la sincera librería Rust clasifica erróneamente vacío como un error recuperable al omitir el campo y, por lo tanto, provoca un bucle de decodificación infinito. Los contenedores que utilizan versiones afectadas de candid están expuestos a una denegación de servicio al hacer que la decodificación se ejecute indefinidamente hasta que el contenedor se bloquea debido a que alcanza el límite máximo de instrucciones por ronda de ejecución. La exposición repetida a el payload dará como resultado un rendimiento degradado del recipiente. Nota: Los botes escritos en Motoko no se ven afectados.