Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.5, Authlib’s JWE zip=DEF path performs unbounded DEFLATE decompression. A very small ciphertext can expand into tens or hundreds of megabytes on decrypt, allowing an attacker who can supply decryptable tokens to exhaust memory and CPU and cause denial of service. This issue has been patched in version 1.6.5. Workarounds for this issue involve rejecting or stripping zip=DEF for inbound JWEs at the application boundary, forking and add a bounded decompression guard via decompressobj().decompress(data, MAX_SIZE)) and returning an error when output exceeds a safe limit, or enforcing strict maximum token sizes and fail fast on oversized inputs; combine with rate limiting.
Fix
Patch, vendor advisory and mitigation references on NVD 2
- https://github.com/authlib/authlib/commit/e0863d5129316b1790eee5f14cece32a03b8184d Patch
- https://github.com/authlib/authlib/security/advisories/GHSA-g7f3-828f-7h7m Exploit, Mitigation, Third Party Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 6.5 · authlibNVD modified 2026-10-19 13:10
Affected (CPE criteria) 1
cpe:2.3:a:authlib:authlib:*:*:*:*:*:*:*:*