Vulnerability · Published Aug 17, 2026 · Assigned by Mattermost

CVE-2026-16049_GitLab Plugin allows cross-channel post injection and phishing via missing channel permission checks in issue API endpoints_

Low 3.9

In plain English

A low-severity missing authorization in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 22% of all known vulnerabilities).

Severity (CVSS 3.1)3.9Low

Exploit odds (30 days)0.3%top 77.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Mattermost Plugins versions <=11.8 10.20.11 11.5.7.0 _The Mattermost GitLab plugin fails to verify channel permissions when processing API requests with a caller-supplied_ {{post_id}}_, and fails to validate the_ {{web_url}} _parameter against the configured GitLab instance, which allows an authenticated attacker to inject bot-authored messages containing arbitrary URLs into channels they do not have access to via the_ {{createIssue}} _and_ {{attachCommentToIssue}} _API endpoints._ Mattermost Advisory ID: MMSA-2026-00673

Affected products (as reported)

Vendor	Product	Versions
Mattermost	Mattermost	0 – through 10.20.110 – through 11.5.7

Weakness: CWE-862 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

References

MMSA-2026-00673 vendor-advisory