Authlib : JWE zip=DEF decompression bomb enables DoS

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2025-62706: 0.46% estimated exploitation activity in the next 30 days; percentile 39.77 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Details - Affected component: Authlib JOSE, JWE zip=DEF (DEFLATE) support. - In authlib/authlib/jose/rfc7518/jwezips.py, DeflateZipAlgorithm.decompress calls zlib.decompress(s, -zlib.MAXWBITS) without a maximum output limit. This permits unbounded expansion of compressed payloads. - In the JWE decode flow (authlib/authlib/jose/rfc7516/jwe.py), when the protected header contains "zip": "DEF", the library routes the decrypted ciphertext into the decompress method and assigns the fully decompressed bytes to the plaintext field before returning it. No streaming limit or quota is applied. - Because DEFLATE achieves extremely high ratios on highly repetitive input, an attacker can craft a tiny zip=DEF ciphertext that inflates…

Published by the source

10 Oct 2025, 22:54 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:35 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-g7f3-828f-7h7m

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-g7f3-828f-7h7m

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# Patch Next advisory brief: CVE-2025-62706

Advisory: Authlib : JWE zip=DEF decompression bomb enables DoS
IDs: CVE-2025-62706, GHSA-g7f3-828f-7h7m
Record: https://patchnext.com/advisories/cve-2025-62706 (revision 2, source checked 26 Oct 2026, 13:35 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: authlib 1.6.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI authlib: affected < 1.6.5; fixed in 1.6.5

## Suggested inspection (read-only)
- `python -m pip show authlib`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on authlib.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-g7f3-828f-7h7m (OSV record GHSA-g7f3-828f-7h7m lists affected ranges: PyPI authlib >=0 <1.6.5 (fixed))
- Verified: https://github.com/advisories/GHSA-g7f3-828f-7h7m (GitHub-reviewed advisory GHSA-g7f3-828f-7h7m lists affected ranges: PyPI authlib >=0 <1.6.5)

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