CVE-2026-6333Network attack vector

Authenticated SSRF via Host-derived slash-command response URL

Published May 18, 2026 · Updated May 18, 2026

SSRF in Mattermost 10.11.0 through 10.11.13 and 11.5.0 through 11.5.1 allows remote authenticated users to redirect slash command responses. tryExecuteCustomCommand builds response_url from the request-derived args.SiteURL, so a spoofed Host header substitutes an attacker-controlled origin. A valid account and an external custom slash command are required; exploitation redirects command responses without reading or interrupting the Mattermost service.

CVSS severity3.5
Low
EPSS probability0.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

SSRF in Mattermost 10.11.0 through 10.11.13 and 11.5.0 through 11.5.1 allows remote authenticated users to redirect slash command responses. tryExecuteCustomCommand builds response_url from the request-derived args.SiteURL, so a spoofed Host header substitutes an attacker-controlled origin. A valid account and an external custom slash command are required; exploitation redirects command responses without reading or interrupting the Mattermost service.

The record

CVE
CVE-2026-6333
Published
May 18, 2026
Updated
May 18, 2026
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-918
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 18, 2026CVE publishedPublication date reported by the CVE source.
  2. May 18, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.11.0 <=10.11.13
  2. Affected versionversion=11.5.0 <=11.5.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=10.11.0 <=10.11.13; version=11.5.0 <=11.5.1

Published CVSS scores

5.0NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N
3.5Mattermost, Inc.CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo