CVE-2026-28802
Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification
HIGH 7.7EPSS 0.6%
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.
- Affected
- authlib
- CVSS v4.0 GITHUB
- 7.7 HIGH
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/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:X/V:X/RE:X/U:X - CVSS v4.0 GitHub
- 7.7 HIGH
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 - CVSS v3.1 NVD
- 9.8 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H - CVSS v3.1 CNA
- 9.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N - EPSS
- 0.57% chance of exploitation in the next 30 days, 46th percentile
- Published
- 2026-03-06
- Updated
- 2026-09-10
Proof-of-concept exploits (1)
Security advisories
- authlib/authlib/security/advisories/GHSA-7wc2-qxgw-g8gg
- authlib/authlib/commit/a61c2acb807496e67f32051b5f1b1d5ccf8f0a75