CVE-2026-28490 Authlib Vulnerable to JWE RSA1_5 Bleichenbacher Padding Oracle
Attackers can exploit a padding oracle in Authlib's RSA1_5 JWE implementation to decrypt sensitive data or bypass security controls.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-28490?
CVE-2026-28490 is a high-severity vulnerability in authlib, published on 16 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. Prior to version 1.6.9, a cryptographic padding oracle vulnerability was identified in the Authlib Python library concerning the implementation of the JSON Web Encryption (JWE) RSA1_5 key management algorithm. Authlib registers RSA1_5 in its default algorithm registry without requiring explicit opt-in, and actively destroys the constant-time Bleichenbacher mitigation that the underlying cryptography library implements correctly. This issue has been patched in version 1.6.9.
Which versions are affected by CVE-2026-28490?
3 open source packages ship an affected version, including authlib. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
authlib PyPI | All versions | 1.6.9 |
authlib PyPI | All versions | 1.6.9 |
authlib PyPI | All versions | 1.6.9 |
Products include Authlib Authlib.
How do I fix CVE-2026-28490?
Upgrade authlib to 1.6.9 or later.
Is CVE-2026-28490 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-28490 exists.
Other vulnerabilities in authlib
- CVE-2026-27962 Authlib JWS JWK Header Injection: Signature Verification Bypass
- CVE-2026-28498 Authlib: Fail-Open Cryptographic Verification in OIDC Hash Binding
- CVE-2026-28802 Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification
- 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-2026-28490, ECHO-c9a3-95ec-f0d8, GHSA-7432-952r-cw78, MINI-3r7v-h68c-mcg4, MINI-jfr7-chc9-99vr, PYSEC-2026-2116 and 2 more.