CVE-2026-6333

SSRF via Host Header Spoofing in Custom Slash Commands

Published May 18, 2026 CVSS 3.1 · 3.5 Low EPSS < 1% KEV · Not listed
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

Remediation

Vendor Solution

Update Mattermost to versions 11.6.0, 11.5.2, 10.11.14 or higher.

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-vqp5-2mrp-qqxg Mattermost doesn't validate the Host header when constructing response URLs for custom slash command
References
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Mattermost mattermost Server
CPEs cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
Vendors & Products Mattermost mattermost Server
Type Values Removed Values Added
First Time appeared Mattermost
Mattermost mattermost
Vendors & Products Mattermost
Mattermost mattermost
Type Values Removed Values Added
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
Title SSRF via Host Header Spoofing in Custom Slash Commands
Weaknesses CWE-918
References
Metrics cvssV3_1

{'score': 3.5, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
Mattermost
Published
Updated
May 19, 2026, 5:19 PM
Reserved
Apr 15, 2026, 8:51 AM
Status
Analyzed
Published
May 18, 2026, 9:16 AM
Modified
Oct 14, 2026, 8:10 PM