What’s Vulnerable › Vulnerabilities

CVE-2026-28802: Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-03-06 · updated 2026-09-10
• Weakness: CWE-347

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.

Affected products

• authlib: from 1.6.5 before 1.6.7 — fixed in 1.6.7

How to fix

Upgrade to a fixed version: authlib 1.6.7. Check the vendor advisory for mitigations.

References

• https://github.com/authlib/authlib/commit/a61c2acb807496e67f32051b5f1b1d5ccf8f0a75
• https://github.com/authlib/authlib/commit/b87c32ed07b8ae7f805873e1c9cafd1016761df7
• https://github.com/authlib/authlib/security/advisories/GHSA-7wc2-qxgw-g8gg
• https://access.redhat.com/errata/RHSA-2026:19375
• https://access.redhat.com/errata/RHSA-2026:4942
• https://access.redhat.com/errata/RHSA-2026:5168
• https://access.redhat.com/errata/RHSA-2026:5665
• https://access.redhat.com/errata/RHSA-2026:6309
• https://access.redhat.com/errata/RHSA-2026:6568
• https://access.redhat.com/security/cve/CVE-2026-28802
• https://bugzilla.redhat.com/show_bug.cgi?id=2445120
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-28802.json

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