CVE-2026-24661 Unbounded Request Body Read in MS Teams Plugin {{/changes}} Webhook Endpoint

What is CVE-2026-24661?

CVE-2026-24661 is a low-severity denial of service vulnerability in Mattermost Mattermost, published on 9 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Mattermost Plugins versions <=2.1.3.0 fail to limit the request body size on the {{/changes}} 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-2026-00611

Weakness: CWE-770

Which versions are affected by CVE-2026-24661?

3 open source packages ship an affected version, including github.com/mattermost/mattermost-plugin-msteams. It affects 1 product.

Products include Mattermost Mattermost.

How do I fix CVE-2026-24661?

Upgrade github.com/mattermost/mattermost-plugin-msteams to 1.15.1-0.20260213190728-6fe4d295592e or later.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-24661 being exploited?

There is no known exploitation of CVE-2026-24661 in the wild and no public exploit code.

Other vulnerabilities in Mattermost Mattermost

• CVE-2019-20851 Path traversal in n/a Critical 9.1
• CVE-2024-39274 Malicious remote can add users to arbitrary teams and channels High 8.7
• CVE-2024-39777 Malicious remote can invite itself to an arbitrary local channel High 8.7
• CVE-2024-39830 Timing attack during remote cluster token comparison when shared channels are enabled High 8.1
• CVE-2023-3615 Lack of server certificate validation in websockets connection High 8.1

All Mattermost Mattermost vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-5rfv-h47g-xj42, GO-2026-5153.