CVE-2026-3116 Improper Input Validation in Zoom Plugin Webhook Handler
An authenticated attacker can cause service disruption in Mattermost by sending oversized requests to the webhook endpoint due to improper input validation.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-3116?
CVE-2026-3116 is a medium-severity denial of service vulnerability in Mattermost Mattermost Server, published on 26 Mar 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Official description
Mattermost Plugins versions <=11.4 11.0.4 11.1.3 11.3.2 10.11.11.0 fail to validate incoming request size which allows an authenticated attacker to cause service disruption via the webhook endpoint. Mattermost Advisory ID: MMSA-2026-00589
Weakness: CWE-400
Which versions are affected by CVE-2026-3116?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-3116?
No fix has been published for CVE-2026-3116 yet. Limit exposure of the affected software until one is available.
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-2026-3116 being exploited?
There is no known exploitation of CVE-2026-3116 in the wild and no public exploit code.
Other vulnerabilities in Mattermost Mattermost Server
- CVE-2025-12419 Account takeover on OAuth/OpenID-enabled servers
- CVE-2025-12421 Account Takeover via Code Exchange Endpoint
- CVE-2025-4981 Path Traversal Leading to RCE by Any Authenticated Mattermost User
- CVE-2025-20051 Arbitrary file read via block duplication in Mattermost Boards
- CVE-2025-25279 Arbitrary file read in Mattermost Boards via import & export board archive
Sources
Also known as GHSA-f499-j7p4-wm44.