vulnerability / NVI-00010557 / Revision 4
Authlib: empty signatures validation in JWS JSON deserialization
GitHub lists this reviewed advisory for authlib. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
9.1 critical
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
9.8 CRITICAL (3.1)
134c704f-9b21-4f2e-91b3-4a467353bcc0 severity; no combined Null risk score.
0.433%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.37781. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
authlib
source listed<= 1.8.0
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 base64 from authlib.jose import JsonWebSignature def b64(b): return base64.urlsafe_b64encode(b).rstrip(b"=").decode() jws =
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
- NVD lastModified does not establish freshness of every associated CPE record.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-6v38-4h7w-rj9h ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-96760 ↗
NIST National Vulnerability Database · official catalog
Observed . This product uses data from the NVD API but is not endorsed or certified by the NVD.
- CVE-2026-96760 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 4 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 3 ·
Source facts changed; compare the preserved prior revision.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.