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Vulnerability record · CVE-2026-49852 · published 17 July 2026

CVE-2026-49852: Improper authentication vulnerability

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.

8.7 CVSS 4.0 High EPSS 0.19% · top 91.8% CWE-287 · Improper authenticationCWE-326 · Inadequate encryption strength Deferred
8.7CVSS 4.0 base score
0.19%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
4References
23 Jul 2026Last modified by NVD

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.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

LinkTags
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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Source: NIST National Vulnerability Database (record CVE-2026-49852), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.