CVE-2026-6333: 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…

PriorityP429medium5CVSS 3.1

AVNACLPRLUINSCCNILAN

EPSS

0.14%

3.5th percentile

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

8 ranges

Vendor	Product	Version range	Fixed in
github.com	mattermost_mattermost-server	>= 0 < 5.3.2-0.20260325160634-e738016c5920	5.3.2-0.20260325160634-e738016c5920
github.com	mattermost_mattermost_server_v8	>= 0 < 8.0.0-20260325160634-e738016c5920	8.0.0-20260325160634-e738016c5920
github.com	mattermost_mattermost_server_v8	>= 10.11.0 < 10.11.14	10.11.14
github.com	mattermost_mattermost_server_v8	>= 11.5.0 < 11.5.2	11.5.2
mattermost	mattermost	10.11.0 – 10.11.13	—
mattermost	mattermost	11.5.0 – 11.5.1	—
mattermost	mattermost_server	>= 10.11.0 < 10.11.14	10.11.14
mattermost	mattermost_server	>= 11.5.0 < 11.5.2	11.5.2

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