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Mattermost doesn't validate user-supplied input in API request handlers

Moderate severity GitHub Reviewed Published May 26, 2026 to the GitHub Advisory Database • Updated Jun 29, 2026

Package

gomod github.com/mattermost/mattermost-plugin-github (Go)

Affected versions

< 1.0.1-0.20260330164815-c2840e980b3c

Patched versions

1.0.1-0.20260330164815-c2840e980b3c
gomod github.com/mattermost/mattermost-server (Go)
= 11.6.0
>= 11.5.0, < 11.5.4
>= 11.4.0, < 11.4.5
>= 10.11.0, < 10.11.15
11.6.1
11.5.4
11.4.5
10.11.15

Description

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

References

Published by the National Vulnerability Database May 22, 2026
Published to the GitHub Advisory Database May 26, 2026
Reviewed Jun 29, 2026
Last updated Jun 29, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(16th percentile)

Weaknesses

Improper Validation of Specified Type of Input

The product receives input that is expected to be of a certain type, but it does not validate or incorrectly validates that the input is actually of the expected type. Learn more on MITRE.

CVE ID

CVE-2026-4646

GHSA ID

GHSA-rmvv-8v8w-rf7x

Source code

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