Vulnerability · Published May 18, 2026 · Assigned by Mattermost
CVE-2026-6333SSRF via Host Header Spoofing in Custom Slash Commands
Low 3.5
In plain English
A low-severity server-side request forgery 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 0.1% (higher than 3% 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 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 & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | 10.11.14+incompatible, 11.5.2+incompatible | GO-2026-5671 |
| Go | github.com/mattermost/mattermost-server | 5.3.2-0.20260325160634-e738016c5920 | GHSA-vqp5-2mrp-qqxg |
| Go | github.com/mattermost/mattermost-server/v5 | no fix listed | GO-2026-5671 |
| Go | github.com/mattermost/mattermost-server/v6 | no fix listed | GO-2026-5671 |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20260325160634-e738016c5920 | GO-2026-5671 |
| Go | github.com/mattermost/mattermost/server/v8 | 10.11.14 | GHSA-vqp5-2mrp-qqxg |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20260325160634-e738016c5920 | GHSA-vqp5-2mrp-qqxg |
| Go | github.com/mattermost/mattermost/server/v8 | 11.5.2 | GHSA-vqp5-2mrp-qqxg |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mattermost | Mattermost | 11.5.0 – through 11.5.110.11.0 – through 10.11.13 |
Weakness: CWE-918 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N
References
- MMSA-2026-00582 vendor-advisory