Vulnerability · Published Jun 12, 2026 · Assigned by Mattermost
CVE-2026-3433Mattermost fails to scope role_updated websocket events to authorized team and channel members
Medium 4.3
In plain English
A medium-severity information exposure 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 0.2% (higher than 8% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to restrict role_updated websocket event broadcasts to members of the affected team or channel which allows an authenticated attacker with guest-level access to observe permission scheme change notifications for private teams they are not a member of via the websocket connection.. Mattermost Advisory ID: MMSA-2026-00616
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | 11.6.1 | GHSA-rp4v-qc77-phm4 |
| Go | github.com/mattermost/mattermost-server | 11.5.5 | GHSA-rp4v-qc77-phm4 |
| Go | github.com/mattermost/mattermost-server | 10.11.17 | GHSA-rp4v-qc77-phm4 |
| Go | github.com/mattermost/mattermost-server | 10.11.17+incompatible, 11.5.5+incompatible, 11.6.1+incompatible | GO-2026-6286 |
| Go | github.com/mattermost/mattermost-server/v5 | no fix listed | GO-2026-6286 |
| Go | github.com/mattermost/mattermost-server/v6 | no fix listed | GO-2026-6286 |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20260504071740-9408b98025d7 | GO-2026-6286 |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20260504071740-9408b98025d7 | GHSA-rp4v-qc77-phm4 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mattermost | Mattermost | 11.6.0 – through 11.6.111.5.0 – through 11.5.410.11.0 – through 10.11.1510.11.0 – through 10.11.16 |
Weakness: CWE-200 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
References
- MMSA-2026-00616 vendor-advisory