Vulnerability · Published Aug 17, 2026 · Assigned by Mattermost

CVE-2026-16047Board channel linking without read channel permission validation

Medium 4.3

In plain English

A medium-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 19% of all known vulnerabilities).

Severity (CVSS 3.1)4.3Medium

Exploit odds (30 days)0.3%top 80.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate that users have read access to a channel before linking a board to it, which allows an authenticated attacker to discover the membership of private channels on the same team via creating, patching, importing, or bulk-creating boards with an arbitrary channelId. Mattermost Advisory ID: MMSA-2026-00674

Affected products (as reported)

Vendor	Product	Versions
Mattermost	Mattermost	11.7.0 – through 11.7.610.11.0 – through 10.11.2111.8.0 – through 11.8.3

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-2026-00674 vendor-advisory