CVE-2025-62706

Publication date 22 October 2025

Last updated 27 February 2026

Ubuntu priority

Cvss 3 Severity Score

Description

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.

Status

Show unmaintained releases

Package	Ubuntu Release	Status
python-authlib	25.10 questing	Vulnerable
	25.04 plucky	Ignored end of life, was needs-triage
	24.04 LTS noble	Fixed 1.3.0-1ubuntu0.1~esm1
	22.04 LTS jammy	Fixed 0.15.5-1ubuntu0.1~esm1

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Severity score breakdown

Parameter	Value
Base score	6.5 · Medium
Attack vector	Network
Attack complexity	Low
Privileges required	Low
User interaction	None
Scope	Unchanged
Confidentiality	None
Integrity impact	None
Availability impact	High
Vector	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

References

Related Ubuntu Security Notices (USN)

USN-8065-1
Authlib vulnerabilities
25 February 2026