CVE-2026-28802
Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification
9.8
CRITICAL
CVSS 3.1
EPSS 0.02%
Description
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.
How to fix CVE-2026-28802
To remediate CVE-2026-28802, upgrade the affected package to a fixed version below.
- —no fix listed
- —upgrade to 1.6.7 or later
Is CVE-2026-28802 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (2)
- from 0
- >= 1.6.5, < 1.6.7
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | 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 |
| osv | CVSS 3.1 | CRITICAL9.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |