Mattermost fails to bound memory allocation when processing PSD image files

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-26246: 0.23% estimated exploitation activity in the next 30 days; percentile 13.96 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to bound memory allocation when processing PSD image files which allows an authenticated attacker to cause server memory exhaustion and denial of service via uploading a specially crafted PSD file. Mattermost Advisory ID: MMSA-2026-00572

Published by the source

16 Mar 2026, 15:30 UTC

Last modified by the source

17 Mar 2026, 19:59 UTC

Source last checked

26 Oct 2026, 15:18 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-44mv-jq72-gj49

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# Patch Next advisory brief: CVE-2026-26246

Advisory: Mattermost fails to bound memory allocation when processing PSD image files
IDs: CVE-2026-26246, GHSA-44mv-jq72-gj49
Record: https://patchnext.com/advisories/cve-2026-26246 (revision 1, source checked 26 Oct 2026, 15:18 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/mattermost/mattermost/server/v8 8.0.0-20260115183946-38b413a27604; github.com/mattermost/mattermost-server 11.3.1, 11.2.3, 10.11.11, 5.3.2-0.20260115183946-38b413a27604. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/mattermost/mattermost/server/v8: affected < 8.0.0-20260115183946-38b413a27604; fixed in 8.0.0-20260115183946-38b413a27604
- Go github.com/mattermost/mattermost-server: affected < 5.3.2-0.20260115183946-38b413a27604; >= 10.11.0-rc1, < 10.11.11; >= 11.2.0-rc1, < 11.2.3; >= 11.3.0-rc1, < 11.3.1; fixed in 11.3.1, 5.3.2-0.20260115183946-38b413a27604, 10.11.11, 11.2.3

## Suggested inspection (read-only)
- Go github.com/mattermost/mattermost/server/v8: check the installed version with your package manager.
- Go github.com/mattermost/mattermost-server: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/mattermost/mattermost/server/v8, github.com/mattermost/mattermost-server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-44mv-jq72-gj49 (GitHub-reviewed advisory GHSA-44mv-jq72-gj49 lists affected ranges: Go github.com/mattermost/mattermost/server/v8 >=0 =0 =10.11.0-rc1 =11.2.0-rc1 =11.3.0-rc1 <11.3.1)

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