Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification
21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 7.7epss 0.4%
exploitation probability
0.4%top 65% of all CVEs
observed exploitation
nono source reports it
Authlib is a Python library which builds OAuth and OpenID Connect servers. From version 1.6.5 to before version 1.6.7, previous tests involving passing a malicious JWT containing alg: none and an empty signature was passing the signature verification step without any changes to the application code when a failure was expected.. This issue has been patched in version 1.6.7.
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:P
Affected products
authlib · authlibReferences
https://access.redhat.com/errata/RHSA-2026:19375https://access.redhat.com/errata/RHSA-2026:4942https://access.redhat.com/errata/RHSA-2026:5168https://access.redhat.com/errata/RHSA-2026:5665https://access.redhat.com/errata/RHSA-2026:6309https://access.redhat.com/errata/RHSA-2026:6568https://access.redhat.com/security/cve/CVE-2026-28802https://bugzilla.redhat.com/show_bug.cgi?id=2445120https://github.com/authlib/authlib/commit/a61c2acb807496e67f32051b5f1b1d5ccf8f0a75https://github.com/authlib/authlib/commit/b87c32ed07b8ae7f805873e1c9cafd1016761df7https://github.com/authlib/authlib/security/advisories/GHSA-7wc2-qxgw-g8gghttps://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-28802.json