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Low, CVSS 3.7

Mattermost MS Teams plugin doesn't limit the request body size on the /lifecycle webhook endpoint

CVE-2026-21388GHSA-x274-8qfc-hrgf

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (github.com/mattermost/mattermost-plugin-msteams 1.15.1-0.20260213190728-6fe4d295592e), 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

Sources

  • GitHub Advisory Database and maintainer security advisories on GitHub

    GitHub-reviewed advisory GHSA-x274-8qfc-hrgf lists affected ranges: Go github.com/mattermost/mattermost-plugin-msteams >=0 <1.15.1-0.20260213190728-6fe4d295592e

    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
3.7 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
EPSS
  • CVE-2026-21388: 0.31% estimated exploitation activity in the next 30 days; percentile 24.04 (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 Plugins versions <=2.3.1 fail to limit the request body size on the {{/lifecycle}} webhook endpoint which allows an authenticated attacker to cause memory exhaustion and denial of service via sending an oversized JSON payload. Mattermost Advisory ID: MMSA-2026-00610.

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

    Published from ghsa record GHSA-x274-8qfc-hrgf

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-2026-21388

Advisory: Mattermost MS Teams plugin doesn't limit the request body size on the /lifecycle webhook endpoint
IDs: CVE-2026-21388, GHSA-x274-8qfc-hrgf
Record: https://patchnext.com/advisories/cve-2026-21388 (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: Low (CVSS 3.7)
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-plugin-msteams 1.15.1-0.20260213190728-6fe4d295592e. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/mattermost/mattermost-plugin-msteams: affected < 1.15.1-0.20260213190728-6fe4d295592e; fixed in 1.15.1-0.20260213190728-6fe4d295592e

## Suggested inspection (read-only)
- 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-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-x274-8qfc-hrgf (GitHub-reviewed advisory GHSA-x274-8qfc-hrgf lists affected ranges: Go github.com/mattermost/mattermost-plugin-msteams >=0 <1.15.1-0.20260213190728-6fe4d295592e)

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