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Mattermost fails to limit the size of responses from integration action endpoints

Moderate severity GitHub Reviewed Published Mar 16, 2026 to the GitHub Advisory Database • Updated Mar 17, 2026

Package

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

Affected versions

< 5.3.2-0.20260127165411-fe3052073dc6
>= 10.11.0-rc1, < 10.11.11
>= 11.2.0-rc1, < 11.2.3
>= 11.3.0-rc1, < 11.3.1

Patched versions

5.3.2-0.20260127165411-fe3052073dc6
10.11.11
11.2.3
11.3.1
gomod github.com/mattermost/mattermost/server/v8 (Go)
< 8.0.0-20260127165411-fe3052073dc6
8.0.0-20260127165411-fe3052073dc6

Description

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 Mattermost fails to limit the size of responses from integration action endpoints, which allows an authenticated attacker to cause server memory exhaustion and denial of service via a malicious integration server that returns an arbitrarily large response when a user clicks an interactive message button. Mattermost Advisory ID: MMSA-2026-00571

References

Published by the National Vulnerability Database Mar 16, 2026
Published to the GitHub Advisory Database Mar 16, 2026
Reviewed Mar 17, 2026
Last updated Mar 17, 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
High
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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:H/PR:N/UI:R/S:U/C:N/I:N/A:H

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.
(6th percentile)

Weaknesses

Memory Allocation with Excessive Size Value

The product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated. Learn more on MITRE.

CVE ID

CVE-2026-2456

GHSA ID

GHSA-34g8-9fpp-46ch

Source code

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