SSRF in Mattermost

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 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

Vulnerability class: SSRF (Server-Side Request Forgery)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 3.5 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.002 (11.7th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 12th percentile — 11.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-6333: held from 0.001 to 0.002.

EPSS over last 30 days · oldest: 0.001 · newest: 0.002 · change: +0.001

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-6333?
CVE-2026-6333 is a low-severity vulnerability in Mattermost, classified under Server-Side Request Forgery (SSRF). CVSS score: 3.5/10. Published 2026-05-18.
How severe is CVE-2026-6333?
Low severity. CVSS v3 base score is 3.5 out of 10.