# CVE-2026-21388: Mattermost MS Teams plugin doesn't limit the request body size on the /lifecycle webhook endpoint

Source: https://junglewise.ai/threats/cve-2026-21388-mattermost-ms-teams-plugin-doesn-t-limit-the-request-body-size-on  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-25  
License: CC BY 4.0 with a link back

CVE-2026-21388 · Severity: low · CVSS 3.1 · Published 2026-06-25

Mattermost MS Teams plugin doesn't limit the request body size on the /lifecycle webhook endpoint in github.com/mattermost/mattermost-plugin-msteams

Technologies: [github.com/mattermost/mattermost-plugin-msteams (Go)](https://junglewise.ai/threats/technologies/github-com-mattermost-mattermost-plugin-msteams). Vendors: [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-21388 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-21388 being exploited in the wild.

**How severe is CVE-2026-21388?** Low severity, with a CVSS score of 3.1, published 25 June 2026.

**Which products and versions are affected?** github.com/mattermost/mattermost-plugin-msteams (Go) SEMVER:introduced=0,fixed=1.15.1-0.20260213190728-6fe4d295592e.

**Is there a fix for CVE-2026-21388?** Yes. github.com/mattermost/mattermost-plugin-msteams (Go): upgrade to 1.15.1-0.20260213190728-6fe4d295592e or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-21388?** Check whether you run github.com/mattermost/mattermost-plugin-msteams (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/mattermost/mattermost-plugin-msteams (Go): upgrade to 1.15.1-0.20260213190728-6fe4d295592e or later

  ```sh
  go get github.com/mattermost/mattermost-plugin-msteams@v1.15.1-0.20260213190728-6fe4d295592e
  ```


## Affected products

- github.com/mattermost/mattermost-plugin-msteams (Go) SEMVER:introduced=0,fixed=1.15.1-0.20260213190728-6fe4d295592e

## Identifiers

- CVE-2026-21388
- GHSA-x274-8qfc-hrgf
- GO-2026-5734

## Related threats

- [Mattermost MS Teams plugin doesn't limit the request body size on the /changes webhook endpoint](https://junglewise.ai/threats/cve-2026-24661-mattermost-ms-teams-plugin-doesn-t-limit-the-request-body-size-on)
- [Mattermost Microsoft Teams Plugin fails to properly mask sensitive configuration values](https://junglewise.ai/threats/cve-2026-2476-mattermost-microsoft-teams-plugin-fails-to-properly-mask-sensitive)
- [GO-2025-3618 - Mattermost vulnerable to Observable Timing Discrepancy in github.com/mattermost/mattermost-plugin-msteams](https://junglewise.ai/threats/cve-2025-27936-mattermost-vulnerable-to-observable-timing-discrepancy)