CVE-2026-28802 PUBLISHED

Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification

Assigner: GitHub_M
Reserved: 03.03.2026 Published: 06.03.2026 Updated: 06.03.2026

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.

Metrics

CVSS 4.0

CVSS Vector: 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 Score: 7.7

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	None	Confidentiality	None
Attack Complexity	Low	Integrity	High	Integrity	None
Attack Requirements	None	Availability	None	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

Product Status

Vendor	authlib
Product	authlib
Versions	Version >= 1.6.5, < 1.6.7 is affected

References

Problem Types

CWE-347: Improper Verification of Cryptographic Signature CWE