Is CVE-2026-53939 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-53939 being exploited in the wild.

How severe is CVE-2026-53939?

Critical severity, with a CVSS score of 9.1, published 9 September 2026.

Which products and versions are affected?

Openidc Cjose 0.6.1 through 0.6.2.5.

Is there a fix for CVE-2026-53939?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-53939 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-53939?

Check whether you run Openidc Cjose at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-53939: OpenIDC cjose all-zero CEK in AES-CBC-HMAC encryption

CVE-2026-53939 · Severity: critical · CVSS 9.1 · Published 2026-09-09

OpenIDC cjose is a cryptographic library used to encrypt sensitive data using industry-standard JOSE (JSON Object Signing and Encryption) protocols. A critical flaw caused the library to encrypt data using a fixed, publicly known all-zero encryption key instead of generating random keys when using certain AES-CBC-HMAC algorithms. This means anyone obtaining an encrypted message can decrypt and forge it, completely compromising the confidentiality and integrity of protected data.

Vendors: Openidc.

Quick answers

Is CVE-2026-53939 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-53939 being exploited in the wild.
How severe is CVE-2026-53939?: Critical severity, with a CVSS score of 9.1, published 9 September 2026.
Which products and versions are affected?: Openidc Cjose 0.6.1 through 0.6.2.5.
Is there a fix for CVE-2026-53939?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-53939 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-53939?: Check whether you run Openidc Cjose at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability is a cryptographic key generation failure in the AES-CBC-HMAC content-encryption code path. The `_cjose_jwe_set_cek_aes_cbc()` function inverted the `random` parameter when allocating the content-encryption key (CEK), causing it to zero-fill the key instead of generating random bytes via `RAND_bytes()`. This affects JWE encryption using AES-CBC-HMAC algorithms (A128CBC-HS256, A192CBC-HS384, A256CBC-HS512) combined with any key-management algorithm except `dir`, including RSA-OAEP, RSA1_5, and AES-KW variants. The resulting ciphertexts are encrypted and authenticated under an all-zero key. AES-GCM and `dir`-mode encryption paths were unaffected. The vulnerability was fixed in version 0.6.2.6 by correcting the parameter passed to `_cjose_jwe_malloc()` and is demonstrated by regression tests confirming CEK randomness across encryptions. Data already encrypted with the zero key cannot be secured retroactively without re-encryption.

Affected products

OpenIDC cjose 0.6.1 through 0.6.2.5

Timeline

2026-09-09: disclosed

References

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