VulnerabilityPublished 29 Oct 2026

CVE-2026-114618: Authlib · Default JWT bearer grant accepts assertions for the wrong audience

Affects mcp-atlassianSource GCVE Database

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Authoritative record:CVE-2026-114618· Medium 6.8

Not known to be exploited · CVSS 6.8 Medium : upgrade to 0.23.1_2 when convenient.

Data as of 30 Oct 2026, 08:32 UTC

CVSS 3.1 base score

6.8Medium

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

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.1	6.8

Patch: Available – fixed in 0.23.1_2

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

Attack Vector: Network
Attack Complexity: High
Privileges Required: Low
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: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
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 22 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 patch is available in Authlib version 0.23.1_2 that fixes this issue by enforcing proper audience validation. Users should upgrade to version 0.23.1_2 or later. Alternatively, overriding the get_audiences() method to return the expected audience(s) enforces strict audience checking and mitigates the vulnerability. Since a fix is available, applying the official patch is the recommended remediation.

Description

Authlib's default implementation of the RFC 7523 JWT bearer grant does not properly validate the 'aud' (audience) claim in JWT assertions. Instead of verifying that the 'aud' claim matches the authorization server's token endpoint, it only checks for the presence of the claim. This allows an attacker with a valid JWT for one audience to use it to obtain access tokens from a different authorization server sharing the same signing key, effectively bypassing audience restrictions.

Impact

An attacker can reuse a JWT assertion issued for one authorization server's audience to obtain access tokens from a different authorization server that shares the same signing key. This bypasses audience restrictions and can lead to unauthorized access tokens being issued, potentially allowing access to protected resources without proper authorization. The CVSS 3.1 score is 6.8 (medium severity) with high impact on confidentiality and integrity but no impact on availability.

Summary

The vulnerability in Authlib's default JWTBearerGrant arises because the default get_audiences() method returns an empty list, causing verify_claims() to only check that the 'aud' claim exists but not validate its value against the expected audience (the token endpoint URL). An attacker who possesses a legitimately issued JWT assertion for any audience can present it to another authorization server that uses the same signing key and obtain an access token. The issue affects the authlib.oauth2.rfc7523.JWTBearerGrant class, the jwt.decode() method with audience validation, and the ResourceProtector.validate_request() method when audience checking is enabled. A proof of concept demonstrates that overriding get_audiences() to enforce strict audience validation correctly rejects JWTs with incorrect audiences, confirming the vulnerability.

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Exploitation evidence

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Affected software

Description

AI analysisMachine-generated, updated 30 Oct 2026, 08:32 UTC

Technical details

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