CVE-2026-114616

Authlib accepts an empty HMAC key, allowing JWS/JWT signature forgery (HS256/HS384/HS512)

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to 1.9.1, Authlib's OctKey.import_key() and HMAC signing and verification path accept zero-length key material. If an application's secret lookup can return an empty string or empty bytes, a remote attacker can compute the deterministic HS256, HS384, or HS512 signature for arbitrary token claims and have Authlib treat the token as authentic. This issue is fixed in version 1.9.1.

Affected

authlib

CVSS v3.1 NVD

9.1 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS v3.1 GITHUB

7.4 HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

0.30% chance of exploitation in the next 30 days, 23rd percentile

Published

2026-10-22

Updated

2026-10-30

Proof-of-concept exploits (1)

• advisories/GHSA-8m4g-j4wp-wgcgfind archive

CVE references

• authlib/authlib/commit/4ff30db442c70e29486e1982cb0ad37c037f5f4bPATCH
• authlib/authlib/releases/tag/v1.9.1REFERENCE
• authlib/authlib/security/advisories/GHSA-8m4g-j4wp-wgcgVENDOR

References

• CVE Record
• NVD entry