Vulnerability · Published Mar 26, 2026 · Assigned by Mattermost
CVE-2026-3115Guest users can view group member IDs without respecting view restrictions
Medium 4.3
In plain English
A medium-severity incorrect 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 0.2% (higher than 15% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to apply view restrictions when retrieving group member IDs, which allows authenticated guest users to enumerate user IDs outside their allowed visibility scope via the group retrieval endpoint.. Mattermost Advisory ID: MMSA-2026-00594
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | 10.11.11+incompatible, 11.2.3+incompatible, 11.3.2+incompatible, 11.4.1+incompatible | GO-2026-5512 |
| Go | github.com/mattermost/mattermost-server/v5 | no fix listed | GO-2026-5512 |
| Go | github.com/mattermost/mattermost-server/v6 | no fix listed | GO-2026-5512 |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20260217110922-b7d4a1f1f59b | GO-2026-5512 |
| Go | github.com/mattermost/mattermost/server/v8 | 11.4.1 | GHSA-mpc7-mm28-f6wq |
| Go | github.com/mattermost/mattermost/server/v8 | 11.3.2 | GHSA-mpc7-mm28-f6wq |
| Go | github.com/mattermost/mattermost/server/v8 | 11.2.3 | GHSA-mpc7-mm28-f6wq |
| Go | github.com/mattermost/mattermost/server/v8 | 10.11.11 | GHSA-mpc7-mm28-f6wq |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20260217110922-b7d4a1f1f59b | GHSA-mpc7-mm28-f6wq |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mattermost | Mattermost | 11.2.0 – through 11.2.210.11.0 – through 10.11.1011.4.0 – through 11.4.011.3.0 – through 11.3.1 |
Weakness: CWE-863 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
References
- MMSA-2026-00594 vendor-advisory