Vulnerability · Published Mar 25, 2026 · Assigned by Mattermost
CVE-2026-26233Denial of Service via HTTP/2 single packet attack on login endpoint
Medium 4.3
In plain English
A medium-severity uncontrolled resource consumption in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 24% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to rate limit login requests which allows unauthenticated remote attackers to cause denial of service (server crash and restart) via HTTP/2 single packet attack with 100+ parallel login requests.. Mattermost Advisory ID: MMSA-2025-00566
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | 11.4.1 | GHSA-247x-7qw8-fp98 |
| Go | github.com/mattermost/mattermost-server | 11.3.2 | GHSA-247x-7qw8-fp98 |
| Go | github.com/mattermost/mattermost-server | 11.2.4 | GHSA-247x-7qw8-fp98 |
| Go | github.com/mattermost/mattermost-server | 10.11.12 | GHSA-247x-7qw8-fp98 |
| Go | github.com/mattermost/mattermost-server | 10.11.12+incompatible, 11.2.4+incompatible, 11.3.2+incompatible, 11.4.1+incompatible | GO-2026-4916 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mattermost | Mattermost | 11.4.0 – through 11.4.011.3.0 – through 11.3.111.2.0 – through 11.2.310.11.0 – through 10.11.11 |
Weakness: CWE-400 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
References
- MMSA-2025-00566 vendor-advisory