CVE-2026-6339
Fixed in a distro release EPSS <1%CVSS 4.3
Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636
Products: Mattermost
Fixed upstream
| Ecosystem | Package | Fixed in |
|---|---|---|
| Go | github.com/mattermost/mattermost-server | 5.3.2-0.20260327001745-7a339a6438f5 |
| Go | github.com/mattermost/mattermost-server | 11.4.4+incompatible |
| Go | github.com/mattermost/mattermost-server | 11.5.2+incompatible |
| Go | github.com/mattermost/mattermost-server/v5 | no fix |
| Go | github.com/mattermost/mattermost-server/v6 | no fix |
| Go | github.com/mattermost/mattermost/server/v8 | 11.5.2 |
| Go | github.com/mattermost/mattermost/server/v8 | 11.4.4 |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20260327001745-7a339a6438f5 |
Distro releases
| Release | Package | Fixed in |
|---|---|---|
| openSUSE Leap 16.0 | govulncheck-vulndb | 0.0.20260723T184607-160000.1.1 |