Host Header Spoofing Vulnerability in Mattermost by Mattermost
CVE-2026-6333

3.5LOW

Key Information:

Vendor

Mattermost
Status
Mattermost
Vendor
CVE Published:
18 May 2026

What is CVE-2026-6333?

Mattermost versions 11.5.x up to 11.5.1 and 10.11.x up to 10.11.13 have a vulnerability due to insufficient validation of the Host header when generating response URLs for custom slash commands. This flaw could allow an authenticated attacker to redirect responses to a malicious server by exploiting a spoofed Host header, posing a significant security risk.

Affected Version(s)

Mattermost 11.5.0 <= 11.5.1

Mattermost 10.11.0 <= 10.11.13

Mattermost 11.6.0

References

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

CVSS V3.1

Score:
3.5
Severity:
LOW
Confidentiality:
None
Integrity:
Low
Availability:
None
Attack Vector:
Network
Attack Complexity:
High
Privileges Required:
Low
User Interaction:
None
Scope:
Changed

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Juho Forsén
.