CVE-2026-53939 Vulnerability Analysis & Exploit Details

CVE-2026-53939 Vulnerability Summary

CVE-2026-53939: OpenIDC/cjose is a C library implementing the Javascript Object Signing and Encryption (JOSE). In versions 0.6.1 through 0.6.2.5, when cjose encrypts a JWE using an AES-CBC-HMAC content-encryption algorithm (`A128CBC-HS256`, `A192CBC-HS384`, or `A256CBC-HS512`) together with any key-management algorithm that generates a fresh content-encryption key (CEK), the CEK is all zero bytes instead of being randomly generated. The resulting JWE is therefore encrypted and authenticated under a fixed, publicly known key, so anyone who obtains the JWE can recover the plaintext and forge or modify the content. This is fixed in version 0.6.2.6 by `_cjose_jwe_set_cek_aes_cbc()` generating the CEK from `RAND_bytes`. A regression test asserts that the `encrypted_key` differs across two encryptions for each AES-CBC-HMAC variant. Until upgrading, for data encrypted with cjose, three options are available. Use an AES-GCM `enc` (`A128GCM` / `A192GCM` / `A256GCM`) instead of an AES-CBC-HMAC `enc`, use `alg=dir` with a caller-supplied CEK, or avoid using cjose for JWE encryption with the affected algorithm pair. These are mitigations for new ciphertexts only; data already encrypted under the zero key remains compromised and should be re-encrypted (and any secrets it contained rotated).

CVE-2026-53939 References

External References

• https://github.com/OpenIDC/cjose/commit/2a6e5bd969fa20059fb00913fb9f57d77ea6a4d9
• https://github.com/OpenIDC/cjose/releases/tag/v0.6.2.6
• https://github.com/OpenIDC/cjose/security/advisories/GHSA-f6wf-pqg3-6wqq
• https://github.com/OpenIDC/cjose/security/advisories/GHSA-f6wf-pqg3-6wqq

CWE Common Weakness Enumeration

CAPEC Common Attack Pattern Enumeration and Classification

• Brute Force CAPEC-112 In this attack, some asset (information, functionality, identity, etc.) is protected by a finite secret value. The attacker attempts to gain access to this asset by using trial-and-error to exhaustively explore all the possible secret values in the hope of finding the secret (or a value that is functionally equivalent) that will unlock the asset.
• Signature Spoofing by Key Recreation CAPEC-485 An attacker obtains an authoritative or reputable signer's private signature key by exploiting a cryptographic weakness in the signature algorithm or pseudorandom number generation and then uses this key to forge signatures from the original signer to mislead a victim into performing actions that benefit the attacker.
• Session Credential Falsification through Prediction CAPEC-59 This attack targets predictable session ID in order to gain privileges. The attacker can predict the session ID used during a transaction to perform spoofing and session hijacking.

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