CVE-2026-28802 Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification
Attackers can bypass JWT signature verification by using the 'none' algorithm, allowing unauthorized access in applications using Authlib.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-28802?
CVE-2026-28802 is a high-severity authentication bypass vulnerability in authlib, published on 6 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-347
Which versions are affected by CVE-2026-28802?
3 open source packages ship an affected version, including authlib. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
authlib PyPI | From 1.6.5 | 1.6.7 |
authlib PyPI | From 1.6.5 | 1.6.7 |
authlib PyPI | From 1.6.5 | 1.6.7 |
Products include Authlib Authlib.
How do I fix CVE-2026-28802?
Upgrade authlib to 1.6.7 or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-28802 being exploited?
There is no known exploitation of CVE-2026-28802 in the wild and no public exploit code.
Other vulnerabilities in authlib
- CVE-2026-27962 Authlib JWS JWK Header Injection: Signature Verification Bypass
- CVE-2026-28490 Authlib Vulnerable to JWE RSA1_5 Bleichenbacher Padding Oracle
- CVE-2026-28498 Authlib: Fail-Open Cryptographic Verification in OIDC Hash Binding
- CVE-2025-61920 Authlib is vulnerable to Denial of Service via Oversized JOSE Segments
- CVE-2025-59420 Authlib: JWS/JWT accepts unknown crit headers (RFC violation → possible authz bypass)
Sources
Also known as DEBIAN-CVE-2026-28802, ECHO-579f-8639-173e, GHSA-7wc2-qxgw-g8gg, MINI-7crv-x7r7-4m48, MINI-8674-jf8j-vqq2, PYSEC-2026-2118 and 2 more.