Mattermost doesn't validate the TIFF IFD offset in the image header before allocating memory

CVE-2026-5755 → View on GitHub ↗ View on CVE.org ↗ View on NVD ↗

Description

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.2, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate the TIFF IFD offset in the image header before allocating memory, which allows authenticated users with file upload or posting permissions to cause a denial of service (server OOM) via uploading a crafted TIFF file or posting a URL that serves one.. Mattermost Advisory ID: MMSA-2026-00648

Basic information

Type
reviewed
Severity
medium
Advisory on GitHub
Open advisory ↗
Repository advisory
—
Source code
Browse source ↗
Published (advisory)
2026-05-26 13:30:15 UTC
Updated
2026-06-29 22:41:11 UTC
GitHub reviewed
2026-06-29 22:41:10 UTC
NVD published
2026-05-22

EPSS Score

Score Percentile
0.24% 15.52%

CVSS Scores

Base score Version Severity Vector
6.5 3.1 —
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/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:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
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-37j2-3vv8-cf24 ↗
CVE CVE-2026-5755 ↗

CWEs

CWE id Name
CWE-400 Uncontrolled Resource Consumption

Affected packages (4)

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 = 11.6.0 11.6.1 —
go github.com/mattermost/mattermost-server >= 11.5.0, < 11.5.4 11.5.4 —
go github.com/mattermost/mattermost-server >= 11.4.0, < 11.4.5 11.4.5 —
go github.com/mattermost/mattermost-server >= 10.11.0, < 10.11.15 10.11.15 —

References

cvelogic Threat Intelligence