VulnerabilityPublished 29 Oct 2026

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

Affects mcpmSource GCVE Database

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Not known to be exploited · CVSS 9.1 Critical : upgrade to 2.15.0_5 as a priority.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score

9.1Critical

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

EPSS: 0.4% chance of exploitation in 30 days – higher than 37% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 2.15.0_5

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 29 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 29 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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), 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 mcpm to 2.15.0_5.

Affected software

Product	Affected	Fixed in
Homebrewmcpm`pkg:brew/mcpm`Other threats	Affected >=2.1.0 <2.15.0_5	Fixed in 2.15.0_5

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A patch is available in Authlib version 2.15.0_5 that fixes this vulnerability by rejecting empty signatures arrays during JSON deserialization. Users should upgrade to version 2.15.0_5 or later to remediate this issue. Until upgraded, avoid calling deserialize_json() on untrusted input or implement additional validation to reject JWS objects with empty signatures arrays.

Description

Authlib versions prior to 2.15.0_5 contain a critical signature verification bypass vulnerability in the JsonWebSignature.deserialize_json() method. This flaw allows an attacker to submit a JSON Web Signature (JWS) object with an empty signatures array, which is incorrectly accepted as valid without any cryptographic verification. This results in an attacker-authored payload being accepted as signed, enabling complete authentication bypass without requiring any key material.

Reports on CVE-2026-96760

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

Impact

Any system relying on Authlib's JsonWebSignature.deserialize_json() to verify JWS JSON Serialization objects is vulnerable to accepting attacker-controlled payloads as validly signed. This leads to a complete authentication bypass, allowing unauthenticated remote attackers to impersonate users or escalate privileges by submitting forged tokens without any cryptographic key. The vulnerability has a high severity with a CVSS score of 9.1, reflecting its critical impact on confidentiality and integrity.

Summary

The vulnerability in Authlib (before 2.15.0_5) arises because the deserialize_json() method initializes a validity flag to true before checking signatures. If the signatures array is empty, the loop that could set the flag to false never runs, causing the method to return the payload as successfully verified without checking any signature or key. This allows an attacker to craft a JWS JSON Serialization object with an empty signatures array and bypass signature verification entirely. The issue is confirmed by tests showing that objects with empty signatures arrays are accepted regardless of key presence, while genuine signatures are properly verified and tampering is detected. The fix involves rejecting empty signatures arrays or initializing the validity flag based on the presence of signatures.

References

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Exploitation evidence

What to do

Affected software

Description

Reports on CVE-2026-96760

AI analysisMachine-generated, updated 30 Oct 2026, 06:59 UTC

Public exploits and detectionGitHub proofs of concept

Technical details

References

Community reviews

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