Mattermost vulnerable to Observable Timing Discrepancy

Exploitation

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

CVSS

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

EPSS

• CVE-2025-27936: 0.34% estimated exploitation activity in the next 30 days; percentile 28.10 (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 Plugin MSTeams versions <2.1.0 and Mattermost Server versions 10.5.x <=10.5.1 with the MS Teams plugin enabled fail to perform constant time comparison on a MSTeams plugin webhook secret which allows an attacker to retrieve the webhook secret of the MSTeams plugin via a timing attack during webhook secret comparison.

Published by the source

16 Apr 2025, 12:31 UTC

Last modified by the source

23 Apr 2025, 15:18 UTC

Source last checked

26 Oct 2026, 15:09 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-2j87-p623-8cc2

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# Patch Next advisory brief: CVE-2025-27936

Advisory: Mattermost vulnerable to Observable Timing Discrepancy
IDs: CVE-2025-27936, GHSA-2j87-p623-8cc2
Record: https://patchnext.com/advisories/cve-2025-27936 (revision 1, source checked 26 Oct 2026, 15:09 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
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 10.5.2, 8.0.0-20250314142426-c049748b8863; github.com/mattermost/mattermost-plugin-msteams 2.1.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/mattermost/mattermost/server/v8: affected >= 10.5.0, < 10.5.2; < 8.0.0-20250314142426-c049748b8863; fixed in 8.0.0-20250314142426-c049748b8863, 10.5.2
- Go github.com/mattermost/mattermost-plugin-msteams: affected <= 1.15.0; fixed in 2.1.0

## Suggested inspection (read-only)
- Go github.com/mattermost/mattermost/server/v8: check the installed version with your package manager.
- Go github.com/mattermost/mattermost-plugin-msteams: 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-plugin-msteams.
- 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-2j87-p623-8cc2 (GitHub-reviewed advisory GHSA-2j87-p623-8cc2 lists affected ranges: Go github.com/mattermost/mattermost/server/v8 >=10.5.0 =0 =0 <=1.15.0)

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