CVE-2026-49852CWE-1391CWE-287CWE-326

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

High · published July 17, 2026

CVSS v4.0
8.7
EPSS
0%
Percentile
8.7
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v4.0
8.7 · HIGH
Vector
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
EPSS
0.00194 · 8.7th percentile
Weaknesses
CWE-1391 · Use of Weak Credentials; CWE-287 · Improper Authentication; CWE-326 · Inadequate Encryption Strength
Published
2026-07-17T19:14Z
EPSS history
Timeline
  • 17 JUL 19:14Z
    joserfc: HS256/HS384/HS512 verify accepts empty/nil HMAC key (cross-language sibling of CVE-2026-45363)
    cvelistv5