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Medium, CVSS 6.5

Mattermost doesn't validate decompressed archive entry sizes during file extraction

CVE-2026-3114GHSA-vhgh-g7x8-4rx8

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (github.com/mattermost/mattermost/server/v8 11.4.1, 11.3.2, 11.2.4, 10.11.12, 8.0.0-20260217110922-b7d4a1f1f59b), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • Go github.com/mattermost/mattermost/server/v8

    Affected
    >= 11.4.0, <= 11.4.0>= 11.3.0, < 11.3.2>= 11.2.0, < 11.2.4>= 10.11.0, < 10.11.12>= 8.0.0-20260105080200-d27a2195068d, < 8.0.0-20260217110922-b7d4a1f1f59b
    Fixed in
    8.0.0-20260217110922-b7d4a1f1f59b, 11.4.1, 11.3.2, 11.2.4, 10.11.12

Sources

  • GitHub Advisory Database and maintainer security advisories on GitHub

    GitHub-reviewed advisory GHSA-vhgh-g7x8-4rx8 lists affected ranges: Go github.com/mattermost/mattermost/server/v8 >=11.4.0 =11.3.0 =11.2.0 =10.11.0 =8.0.0-20260105080200-d27a2195068d <8.0.0-20260217110922-b7d4a1f1f59b

    VerifiedObserved Structured GitHub Advisory Database record (type=reviewed) from the GitHub REST API.

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
6.5 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-3114: 0.36% estimated exploitation activity in the next 30 days; percentile 29.38 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to validate decompressed archive entry sizes during file extraction which allows authenticated users with file upload permissions to cause a denial of service via crafted zip archives containing highly compressed entries (zip bombs) that exhaust server memory. Mattermost Advisory ID: MMSA-2026-00598.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-vhgh-g7x8-4rx8

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-3114

Advisory: Mattermost doesn't validate decompressed archive entry sizes during file extraction
IDs: CVE-2026-3114, GHSA-vhgh-g7x8-4rx8
Record: https://patchnext.com/advisories/cve-2026-3114 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
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 11.4.1, 11.3.2, 11.2.4, 10.11.12, 8.0.0-20260217110922-b7d4a1f1f59b. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/mattermost/mattermost/server/v8: affected >= 11.4.0, <= 11.4.0; >= 11.3.0, < 11.3.2; >= 11.2.0, < 11.2.4; >= 10.11.0, < 10.11.12; >= 8.0.0-20260105080200-d27a2195068d, < 8.0.0-20260217110922-b7d4a1f1f59b; fixed in 8.0.0-20260217110922-b7d4a1f1f59b, 11.4.1, 11.3.2, 11.2.4, 10.11.12

## Suggested inspection (read-only)
- Go github.com/mattermost/mattermost/server/v8: 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.
- 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-vhgh-g7x8-4rx8 (GitHub-reviewed advisory GHSA-vhgh-g7x8-4rx8 lists affected ranges: Go github.com/mattermost/mattermost/server/v8 >=11.4.0 =11.3.0 =11.2.0 =10.11.0 =8.0.0-20260105080200-d27a2195068d <8.0.0-20260217110922-b7d4a1f1f59b)

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