CVE-2026-10819 Mattermost Server Denial of Service via Animated GIF Emoji Upload
An authenticated attacker can cause a denial of service by uploading a crafted animated GIF as a custom emoji due to missing frame and size limits.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-10819?
CVE-2026-10819 is a medium-severity denial of service vulnerability in Mattermost Mattermost Server, published on 27 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Mattermost versions 11.6.x <= 11.6.5, 10.11.x <= 10.11.20, 11.8.x <= 11.8.1, 11.7.x <= 11.7.4 fail to limit the number of frames and enforce the file size cap on animated GIF uploads, which allows an authenticated attacker to cause a denial of service via a crafted animated GIF uploaded as a custom emoji.. Mattermost Advisory ID: MMSA-2026-00695
Weakness: CWE-409
Which versions are affected by CVE-2026-10819?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-10819?
Upgrade to a fixed version.
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-2026-10819 being exploited?
There is no known exploitation of CVE-2026-10819 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-qf49-6jm2-h67m, MINI-74rm-gfrh-957f, MINI-cg48-mcf3-cf32.