Medium severity · published May 18, 2026
CVE-2026-6333
SSRF via Host Header Spoofing in Custom Slash Commands
5.0
CVSS
0.1%
EPSS
No
On KEV
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
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.1% · higher than 3% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
11.5.0 through 11.5.1; 10.11.0 through 10.11.13 · source: vendor
MS
Mattermost Server · Mattermost
10.11.0 before 10.11.14; 11.5.0 before 11.5.2 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-6333
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-6333
Vendor Advisory
https://mattermost.com/security-updates
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