High severity · published Jul 17, 2026
CVE-2026-49852
joserfc: HS256/HS384/HS512 verify accepts empty/nil HMAC key (cross-language sibling of CVE-2026-45363)
8.7
CVSS
0.2%
EPSS
No
On KEV
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.
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 6% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
JO
joserfc · authlib
< 1.6.8 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-49852
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-49852
github.com
https://github.com/authlib/joserfc/commit/86d00910b2b2d2d07503fee9b572906daefab7f1
github.com
https://github.com/authlib/joserfc/releases/tag/1.6.8
github.com
https://github.com/authlib/joserfc/security/advisories/GHSA-gg9x-qcx2-xmrh
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