CVE-2026-6333
Low
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
SeverityLow
CVSS3.5
Exploit probability—
Product
Mattermost Server
PublishedMay 18, 2026
First seenMay 18, 2026
Weakness typeCWE-918Server-side request forgery (SSRF)
How to fix
Update
- mattermost mattermost_server10.11.14, 11.5.2 or later
- github.com/mattermost/mattermost/server/v811.5.2, 10.11.14, 8.0.0-20260325160634-e738016c5920 or later
- github.com/mattermost/mattermost-server5.3.2-0.20260325160634-e738016c5920, 10.11.14+incompatible, 11.5.2+incompatible or later
Vendor advisories
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mattermost mattermost_server | 10.11.0 ≤ v < 10.11.14, 11.5.0 ≤ v < 11.5.2 | 10.11.14, 11.5.2 |
| github.com/mattermost/mattermost/server/v8Go | 11.5.0 ≤ v < 11.5.2, 10.11.0 ≤ v < 10.11.14, v < 8.0.0-20260325160634-e738016c5920 | 11.5.2, 10.11.14, 8.0.0-20260325160634-e738016c5920 |
| github.com/mattermost/mattermost-serverGo | v < 5.3.2-0.20260325160634-e738016c5920, 10.11.0+incompatible ≤ v < 10.11.14+incompatible, 11.5.0+incompatible ≤ v < 11.5.2+incompatible | 5.3.2-0.20260325160634-e738016c5920, 10.11.14+incompatible, 11.5.2+incompatible |
| github.com/mattermost/mattermost-server/v5Go | No range specified | — |
| github.com/mattermost/mattermost-server/v6Go | No range specified | — |
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