CVE-2026-118669VulnerabilityPublished 31 Oct 2026

mcp-atlassian · OAuthLib: Token grants can use attacker-supplied client_id for authorization after authenticating a different client

Affects mcp-atlassianSource GCVE Database

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Authoritative record:CVE-2026-118669· High 8.4

Not known to be exploited · CVSS 8.4 High : upgrade to 0.23.1_1 soon.

Data as of 31 Oct 2026, 16:52 UTC

CVSS 4.0 base score

8.4High

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 4.0	8.4

Patch: Available – fixed in 0.23.1_1

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:H/SI:H/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: Low
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: High
Vulnerable system availability: None
Subsequent system confidentiality: High
Subsequent system integrity: High
Subsequent system availability: None

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: Low: The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system 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 vulnerable system. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the vulnerable system.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: High: There is a total loss of confidentiality, resulting in all resources within the Subsequent System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
Subsequent system 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 Subsequent System. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the Subsequent System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 28 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 30 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_1.

Affected software

Product	Affected	Fixed in
Homebrewmcp-atlassian`pkg:brew/mcp-atlassian`Other threats	Affected >=0.11.9 <0.23.1_1	Fixed in 0.23.1_1

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 OAuthlib version 0.23.1_1 that addresses this issue. Users should upgrade to version 0.23.1_1 or later to remediate this vulnerability. Until patched, applications should ensure their RequestValidator implementations do not rely solely on the client_id argument passed by OAuthlib for authorization decisions and instead strictly verify that the authenticated client matches the client_id used in grant and scope validation.

Description

OAuthlib contains a vulnerability in its token grant handlers where an authenticated low-privilege client can supply a different client_id in the token request body, causing grant and scope validation to be performed under that other client identity. This affects the client_credentials and password grant flows. The issue arises because OAuthlib does not require the authenticated client's client_id to match the client_id parameter in the request body, allowing authorization checks to be bypassed. This can lead to unauthorized issuance of tokens with elevated scopes or grant types. A fix is available in version 0.23.1_1.

Impact

An attacker with valid credentials for a low-privilege confidential client can exploit this vulnerability to obtain access tokens with scopes and grant types assigned to a different, higher-privilege client. This results in token authorization bypass, allowing unauthorized access to resources or actions that should be restricted. The attack requires authentication as a client but does not require user interaction or elevated privileges beyond the compromised client credentials.

Summary

OAuthlib's token grant handlers for the client_credentials and password grant types authenticate a client and set request.client accordingly. However, OAuthlib does not enforce that request.client_id matches request.client.client_id. If the request body contains a client_id parameter, OAuthlib retains this attacker-supplied value and uses it in validate_grant_type() and validate_scopes(), leading to a mismatch between the authenticated client and the client_id used for authorization. This allows an attacker with credentials for a low-privilege client to obtain tokens authorized under a higher-privilege client's grants and scopes, effectively bypassing intended authorization restrictions. The vulnerability is fixed in version 0.23.1_1.

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Affected software

Description

AI analysisMachine-generated, updated 31 Oct 2026, 16:52 UTC

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