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CVE-2026-6333

SSRF via Host Header Spoofing in Custom Slash Commands

Published: May 18, 2026Updated: May 19, 2026 Sources: CVE List NVDCWE-918
NVD MITRE
3.5CVSSLOW
EPSS Score
0.1%
Top 96.6%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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

CVSS Vector Breakdown

AV:NAC:HPR:LUI:NS:CC:NI:LA:N
Exploitability
AV:NAttack Vector
Network
AC:HAttack Complexity
High
PR:LPrivileges Required
Low
UI:NUser Interaction
None
Scope
S:CScope
Changed
Impact
C:NConfidentiality
None
I:LIntegrity
Low
A:NAvailability
None
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Weaknesses

CWE-918

Affected Products

mattermost servermattermost
On-premWeb App
Communications / messaging-chat
MattermostMattermost
On-premWeb App
Communications / messaging-chat
mattermostcommercialUSCommunications

Attack Graph

Products CVE Techniques Tactics

Click technique nodes to view MITRE ATT&CK details. Scroll to zoom, drag to pan.

Exploitability

Official Patch Available

MITRE ATT&CK

2 techniques
Command and Control
Initial Access
View detailed technique mapping

References

https://mattermost.com/security-updates
mattermost.com

Timeline

Published
May 18, 2026
Last Updated
May 19, 2026

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