What is the CVSS score of CVE-2026-4646?

CVE-2026-4646 has a CVSS 3.1 base score of 4.3 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L. EPSS exploitation probability: 0.2%.

Is there a patch available for CVE-2026-4646?

Yes, a patch is available for CVE-2026-4646. Update the affected software to the latest version immediately.

Mattermost CVE-2026-4646

Q: Which versions of Mattermost are affected by CVE-2026-4646?

Authenticated denial-of-service in Mattermost's plugin subsystem allows a low-privileged user to crash the plugin process by sending a crafted HTTP request to the PR details API endpoint.. A patch is available.

EUVD-2026-31430 MEDIUM

Improper Validation of Specified Type of Input (CWE-1287)

2026-05-22 Mattermost

GHSA-rmvv-8v8w-rf7x

Denial Of Service Mattermost

4.3

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

4.3 MEDIUM

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

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

Low

Lifecycle Timeline

Analysis Generated

May 22, 2026 - 11:32 vuln.today

DescriptionCVE.org

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate user-supplied input in API request handlers which allows an authenticated attacker to crash the plugin process via a crafted HTTP request to the PR details endpoint.. Mattermost Advisory ID: MMSA-2026-00638

AnalysisAI

Authenticated denial-of-service in Mattermost's plugin subsystem allows a low-privileged user to crash the plugin process by sending a crafted HTTP request to the PR details API endpoint. Affected across four active release branches (10.11.x, 11.4.x, 11.5.x, 11.6.x), the flaw stems from missing input validation in API request handlers (CWE-1287). No public exploit code exists and the vulnerability is not listed in CISA KEV; however, the low authentication barrier (any valid account) combined with network accessibility makes it a realistic insider or post-compromise nuisance risk.

Technical ContextAI

The root cause is CWE-1287 (Improper Validation of Specified Type of Input): Mattermost's API request handlers for the PR details endpoint accept user-controlled data without enforcing expected type or structure constraints, allowing a malformed payload to reach the plugin runtime in an unexpected state and trigger a process crash. The affected component is the Mattermost server application (CPE: cpe:2.3:a:mattermost:mattermost:*:*:*:*:*:*:*:*), specifically the plugin management layer that exposes a PR (pull request) details endpoint - indicative of an integration plugin (e.g., GitHub or GitLab connector). The CVSS vector AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L confirms a network-reachable attack of low complexity, requiring only a standard authenticated session, with impact scoped to availability at a limited (plugin-process) level rather than the full Mattermost service. Advisory reference MMSA-2026-00638 and ENISA EUVD-2026-31430 corroborate the vendor-reported scope.

RemediationAI

Upgrade Mattermost to a version beyond the affected ranges per the vendor advisory at https://mattermost.com/security-updates. The advisory covers patched releases across all affected branches (10.11.x, 11.4.x, 11.5.x, 11.6.x), but exact fixed version numbers are not explicitly stated in the available intelligence data - consult the vendor advisory directly to confirm the minimum safe version for each branch. If immediate upgrade is not feasible, a compensating control is to restrict API access to the PR details endpoint at the network or reverse-proxy layer, limiting it to trusted internal IP ranges; note this may break legitimate integrations relying on that endpoint. Additionally, enforcing strict user account hygiene (disabling dormant accounts, auditing who holds active sessions) reduces the pool of potential authenticators who could abuse the flaw.