What’s Vulnerable › Vulnerabilities

CVE-2026-49852: joserfc: HS256/HS384/HS512 verify accepts empty/nil HMAC key (cross-language sibling of CVE-2026-45363)

• Severity: high (CVSS 8.7 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-17 · updated 2026-10-24
• Weakness: CWE-287

Description

joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to 1.6.8, joserfc.jwt.decode accepts attacker-forged HMAC-signed tokens when the caller-supplied verification key is the empty string or None, because HMACAlgorithm.sign and HMACAlgorithm.verify in src/joserfc/_rfc7518/jws_algs.py pass the output of OctKey.get_op_key(...) to hmac.new(...) and OctKey.import_key in src/joserfc/_rfc7518/oct_key.py only emits a SecurityWarning for keys shorter than 14 bytes without rejecting zero-length input. This issue is fixed in version 1.6.8.

Affected products

• authlib joserfc: before 1.6.8

References

• https://github.com/authlib/joserfc/commit/86d00910b2b2d2d07503fee9b572906daefab7f1
• https://github.com/authlib/joserfc/releases/tag/1.6.8
• https://github.com/authlib/joserfc/security/advisories/GHSA-gg9x-qcx2-xmrh
• https://github.com/authlib/joserfc/security/advisories/GHSA-gg9x-qcx2-xmrh

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