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

CVE-2026-2456 → View on GitHub ↗ View on CVE.org ↗ View on NVD ↗

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

Basic information

Type
reviewed
Severity
medium
Advisory on GitHub
Open advisory ↗
Repository advisory
—
Source code
Browse source ↗
Published (advisory)
2026-03-16 15:30:43 UTC
Updated
2026-03-17 20:01:23 UTC
GitHub reviewed
2026-03-17 20:01:22 UTC
NVD published
2026-03-16 14:19:29 UTC

EPSS Score

Score Percentile
0.04% 12.51%

CVSS Scores

Base score Version Severity Vector
5.3 3.1 —
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.

Identifiers

Type Value
GHSA GHSA-34g8-9fpp-46ch ↗
CVE CVE-2026-2456 ↗

CWEs

CWE id Name
CWE-789 Memory Allocation with Excessive Size Value

Affected packages (5)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
go github.com/mattermost/mattermost/server/v8 < 8.0.0-20260127165411-fe3052073dc6 8.0.0-20260127165411-fe3052073dc6 —
go github.com/mattermost/mattermost-server < 5.3.2-0.20260127165411-fe3052073dc6 5.3.2-0.20260127165411-fe3052073dc6 —
go github.com/mattermost/mattermost-server >= 10.11.0-rc1, < 10.11.11 10.11.11 —
go github.com/mattermost/mattermost-server >= 11.2.0-rc1, < 11.2.3 11.2.3 —
go github.com/mattermost/mattermost-server >= 11.3.0-rc1, < 11.3.1 11.3.1 —

References

cvelogic Threat Intelligence