Authlib: empty signatures validation in JWS JSON deserialization

Exploitation

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

CVSS

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

EPSS

• CVE-2026-96760: 0.43% estimated exploitation activity in the next 30 days; percentile 37.65 (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.

Authlib (prior to 1.9.0) contains a signature verification bypass vulnerability. The JsonWebSignature.deserialize_json() method accepts a JSON Serialization JWS object and returns the payload as successfully verified without checking for a signature and without requiring a cryptographic key.

Root cause `authlib/jose/rfc7515/jws.py`, read on the installed 1.8.0 artifact: ```python is_valid = True

set before anything is checked for header_obj in obj["signatures"]:

empty array means the body never runs jws_header, valid = self._validate_json_jws(...) if not valid: is_valid = False ... if is_valid: return rv

returns the payload as verified ``` `is_valid` is initialised to `True` and only ever set to `False` from inside the loop. A JWS JSON Serialization object whose `signatures` array is empty iterates zero times, so the flag survives and the payload is returned as successfully verified. No key is consulted, because no signature is examined.

Reproduction ```python import…

Published by the source

27 Oct 2026, 14:50 UTC

Last modified by the source

27 Oct 2026, 15:00 UTC

Source last checked

28 Oct 2026, 06:10 UTC

1. Revision 2 · amended · 28 Oct 2026

   Amended from osv record GHSA-6v38-4h7w-rj9h

2. Revision 1 · created · 27 Oct 2026

   Published from ghsa record GHSA-6v38-4h7w-rj9h

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# Patch Next advisory brief: CVE-2026-96760

Advisory: Authlib: empty signatures validation in JWS JSON deserialization
IDs: CVE-2026-96760, GHSA-6v38-4h7w-rj9h
Record: https://patchnext.com/advisories/cve-2026-96760 (revision 2, source checked 28 Oct 2026, 06:10 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: authlib 1.9.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI authlib: affected < 1.9.0; fixed in 1.9.0

## 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-6v38-4h7w-rj9h (OSV record GHSA-6v38-4h7w-rj9h lists affected ranges: PyPI authlib >=0 <1.9.0 (fixed))
- Verified: https://github.com/advisories/GHSA-6v38-4h7w-rj9h (GitHub-reviewed advisory GHSA-6v38-4h7w-rj9h lists affected ranges: PyPI authlib >=0 <=1.8.0)

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