Vulnerability · Published May 15, 2026 · Assigned by Mattermost
CVE-2026-4054SVG content served through Mattermost image proxy despite Content-Type restrictions causes client-side denial of service
Medium 4.3
In plain English
A medium-severity security flaw 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 0.2% (higher than 15% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 Fail to validate the response body of proxied images, which allows a remote attacker to enact client-side DoS via an SVG file served from an attacker-controlled origin under a non-SVG Content-Type header (e.g. image/png) embedded in an og:image meta tag or Markdown image link.. Mattermost Advisory ID: MMSA-2026-00630
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | 11.5.2 | GHSA-j76w-p754-g2w7 |
| Go | github.com/mattermost/mattermost-server | 0.0.0-20260414103857-b21ef302025e | GHSA-j76w-p754-g2w7 |
| Go | github.com/mattermost/mattermost-server | 11.4.4 | GHSA-j76w-p754-g2w7 |
| Go | github.com/mattermost/mattermost-server | 0.0.0-20260414103857-b21ef302025e, 11.4.4+incompatible, 11.5.2+incompatible | GO-2026-5454 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mattermost | Mattermost | 11.5.0 – through 11.5.110.11.0 – through 10.11.1311.4.0 – through 11.4.3 |
Weakness: CWE-754 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L
References
- MMSA-2026-00630 vendor-advisory