MEDIUM 4.3
GHSA-j76w-p754-g2w7
Mattermost doesn't validate the response body of proxied images
Details
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.
Are you affected?
Enter the version of the package you're using.
Affected packages
Go / github.com/mattermost/mattermost-server
Introduced in:
11.5.0 Fixed in: 11.5.2 Fix
go get github.com/mattermost/mattermost-server@v11.5.2 Go / github.com/mattermost/mattermost-server
Introduced in:
0.0.0-20250731163400-5b955468ea1e Fixed in: 0.0.0-20260414103857-b21ef302025e Fix
go get github.com/mattermost/mattermost-server@v0.0.0-20260414103857-b21ef302025e Go / github.com/mattermost/mattermost-server
Introduced in:
11.4.0 Fixed in: 11.4.4 Fix
go get github.com/mattermost/mattermost-server@v11.4.4