VulnerabilityPublished 29 Oct 2026

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

Affects mcp-atlassianSource GCVE Database

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Not known to be exploited · CVSS 9.1 Critical : upgrade to 0.23.1_2 as a priority.

Data as of 30 Oct 2026, 08:31 UTC

CVSS 3.1 base score

9.1Critical

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

Patch: Available – fixed in 0.23.1_2

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 mcp-atlassian to 0.23.1_2.

Affected software

Product	Affected	Fixed in
Homebrewmcp-atlassian`pkg:brew/mcp-atlassian`Other threats	Affected >=0.11.11 <0.23.1_2	Fixed in 0.23.1_2

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

AI-suggested

A fix is available in Authlib version 0.23.1_2 that addresses this vulnerability by rejecting empty signatures arrays during JWS JSON deserialization. Users should upgrade to version 0.23.1_2 or later to remediate this issue. Until upgraded, avoid deserializing untrusted JWS JSON objects or implement additional signature presence checks before accepting payloads.

Description

Authlib versions prior to 0.23.1_2 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. As a result, attacker-crafted payloads can be accepted as authenticated, leading to a complete authentication bypass. The issue is fixed in version 0.23.1_2.

Reports on CVE-2026-96760

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

Impact

An unauthenticated remote attacker can bypass signature verification and cause the system to accept attacker-controlled payloads as validly signed. This leads to a complete authentication bypass, allowing unauthorized access or privilege escalation wherever Authlib's vulnerable JWS deserialization is used to verify identity or authorization claims.

Summary

Authlib before version 0.23.1_2 has a vulnerability in the JsonWebSignature.deserialize_json() method where the signature verification logic initializes a validity flag to true and only sets it to false if invalid signatures are found in the signatures array. If the signatures array is empty, the loop does not run, and the payload is returned as verified without any signature checks or key usage. This allows an attacker to bypass signature verification by submitting a JWS JSON Serialization object with an empty signatures array, effectively bypassing authentication. The vulnerability was demonstrated with proof-of-concept code and is fixed by rejecting empty signatures arrays or initializing the validity flag based on the presence of signatures.

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

Reports on CVE-2026-96760

AI analysisMachine-generated, updated 30 Oct 2026, 08:31 UTC

Public exploits and detectionGitHub proofs of concept

Technical details

References

Community reviews

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