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Vulnerability · Published Mar 6, 2026 · Assigned by GitHub_M

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

Critical 9.1

In plain English

A critical-severity security flaw in authlib from authlib. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 45% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.1Critical
Exploit odds (30 days)0.5%top 54.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:13python-authlibno fix listedDEBIAN-CVE-2026-28802
Debian:14python-authlib1.6.7-1DEBIAN-CVE-2026-28802
PyPIauthlib1.6.7GHSA-7wc2-qxgw-g8gg
PyPIauthlib1.6.7PYSEC-2026-2118
Ubuntu:25.10python-authlibno fix listedUBUNTU-CVE-2026-28802

Affected products (as reported)

VendorProductVersions
authlib authlib >= 1.6.5, < 1.6.7

Weakness: CWE-347 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

References