CVE-2026-6333
LOW3.5EPSS 0.03%Mattermost doesn't validate the Host header when constructing response URLs for custom slash command
Published: 5/18/2026Modified: 6/1/2026
Description
Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to validate the Host header when constructing response URLs for custom slash commands which allows an authenticated attacker to redirect slash command responses to an attacker-controlled server via a spoofed Host header.. Mattermost Advisory ID: MMSA-2026-00582
Affected packages (2)
- Go/github.com/mattermost/mattermost-serverfrom 0, < 5.3.2-0.20260325160634-e738016c5920
- Go/github.com/mattermost/mattermost/server/v8>= 11.5.0, < 11.5.2
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | LOW3.5 | CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N |