A vulnerability has been identified in the JSON Web Encryption (JWE) decryption interfaces, specifically related to the support for decompressing plaintext after its decryption. This allows an adversary to exploit specific scenarios where the compression ratio becomes exceptionally high. As a result, the length of the JWE token, which is determined by the compressed content's size, can land below application-defined limits. In such cases, other existing application level mechanisms for preventing resource exhaustion may be rendered ineffective.

Note that as per RFC 8725 compression of data SHOULD NOT be done before encryption, because such compressed data often reveals information about the plaintext. For this reason the v5.x major version of jose removed support for compressed payloads entirely and is therefore NOT affected by this advisory.

Impact

Under certain conditions it is possible to have the user's environment consume unreasonable amount of CPU time or memory during JWE Decryption operations.

Affected users

The impact is limited only to Node.js users utilizing the JWE decryption APIs to decrypt JWEs from untrusted sources.

You are NOT affected if any of the following applies to you

- Your code uses jose version v5.x where JWE Compression is not supported anymore - Your code runs in an environment other than Node.js (e.g. Deno, CF Workers), which is the only runtime where JWE Compression is implemented out of the box - Your code does not use the JWE decryption APIs - Your code only accepts JWEs produced by trusted sources

Patches

v2.0.7 and v4.15.5 releases limit the decompression routine to only allow decompressing up to 250 kB of plaintext. In v4.x it is possible to further adjust this limit via the inflateRaw decryption option implementation. In v2.x it is possible to further adjust this limit via the inflateRawSyncLimit decryption option.

Workarounds

If you cannot upgrade and do not want to support compressed JWEs you may detect and reject these tokens early by checking the token's protected header

js const { zip } = jose.decodeProtectedHeader(token) if (zip !== undefined) { throw new Error('JWE Compression is not supported') }

If you wish to continue supporting JWEs with compressed payloads in these legacy release lines you must upgrade (v1.x and v2.x to version v2.0.7, v3.x and v4.x to version v4.15.5) and review the limits put forth by the patched releases.

For more information If you have any questions or comments about this advisory please open a discussion in the project's repository

jose is an npm library providing a number of cryptographic operations. In vulnerable versions AESCBCHMACSHA2 Algorithm (A128CBC-HS256, A192CBC-HS384, A256CBC-HS512) decryption would always execute both HMAC tag verification and CBC decryption, if either failed JWEDecryptionFailed would be thrown. A possibly observable difference in timing when padding error would occur while decrypting the ciphertext makes a padding oracle and an adversary might be able to make use of that oracle to decrypt data without knowing the decryption key by issuing on average 128b calls to the padding oracle (where b is the number of bytes in the ciphertext block). All major release versions have had a patch released which ensures the HMAC tag is verified before performing CBC decryption. The fixed versions are ^1.28.1 || ^2.0.5 || >=3.11.4. Users should upgrade their v1.x dependency to ^1.28.1, their v2.x dependency to ^2.0.5, and their v3.x dependency to ^3.11.4. Thanks to Jason from Microsoft Vulnerability Research (MSVR) for bringing this up and Eva Sarafianou (@esarafianou) for helping to score this advisory.

JOSE is "JSON Web Almost Everything" - JWA, JWS, JWE, JWT, JWK, JWKS with no dependencies using runtime's native crypto in Node.js, Browser, Cloudflare Workers, Electron, and Deno. The PBKDF2-based JWE key management algorithms expect a JOSE Header Parameter named p2c PBES2 Count, which determines how many PBKDF2 iterations must be executed in order to derive a CEK wrapping key. The purpose of this parameter is to intentionally slow down the key derivation function in order to make password brute-force and dictionary attacks more expensive. This makes the PBES2 algorithms unsuitable for situations where the JWE is coming from an untrusted source: an adversary can intentionally pick an extremely high PBES2 Count value, that will initiate a CPU-bound computation that may take an unreasonable amount of time to finish. Under certain conditions, it is possible to have the user's environment consume unreasonable amount of CPU time. The impact is limited only to users utilizing the JWE decryption APIs with symmetric secrets to decrypt JWEs from untrusted parties who do not limit the accepted JWE Key Management Algorithms (alg Header Parameter) using the keyManagementAlgorithms (or algorithms in v1.x) decryption option or through other means. The v1.28.2, v2.0.6, v3.20.4, and v4.9.2 releases limit the maximum PBKDF2 iteration count to 10000 by default. It is possible to adjust this limit with a newly introduced maxPBES2Count decryption option. If users are unable to upgrade their required library version, they have two options depending on whether they expect to receive JWEs using any of the three PBKDF2-based JWE key management algorithms. They can use the keyManagementAlgorithms decryption option to disable accepting PBKDF2 altogether, or they can inspect the JOSE Header prior to using the decryption API and limit the PBKDF2 iteration count (p2c Header Parameter).