Answer in brief
CVE-2026-3433 records a Medium severity (CVSS 4.3) vulnerability in Mattermost doesn't restrict role_updated websocket event broadcasts to members of the affected team or channel. The current sources do not mark it as known exploited. The current feed maps github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go) and additional mapped packages. Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 4.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go) and additional mapped packages. Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| github.com/mattermost/mattermost-servergo | =11.6.0 | 11.6.1 |
| github.com/mattermost/mattermost-servergo | >=11.5.0,<=11.5.4 | 11.5.5 |
| github.com/mattermost/mattermost-servergo | >=10.11.0,<=10.11.15 | 10.11.17 |
| github.com/mattermost/mattermost-servergo | >=11.6.0 <11.6.1 | 11.6.1 |
| github.com/mattermost/mattermost-servergo | >=11.5.0 <11.5.5 | 11.5.5 |
| github.com/mattermost/mattermost-servergo | >=10.11.0 <10.11.17 | 10.11.17 |
| github.com/mattermost/mattermost/server/v8go | >=8.0.0-20250731163400-5b955468ea1e,<8.0.0-20260504071740-9408b98025d7 | 8.0.0-20260504071740-9408b98025d7 |
| github.com/mattermost/mattermost/server/v8go | >=8.0.0-20250731163400-5b955468ea1e <8.0.0-20260504071740-9408b98025d7 | 8.0.0-20260504071740-9408b98025d7 |
Published upstream
Jun 12, 2026
Evidence: source:ghsa:source_dates:source-dates:recordSource modified
Aug 24, 2026
Evidence: source:ghsa:source_dates:source-dates:recordFirst seen by HOL
Aug 25, 2026
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
Quoted source text, attributed separately from HOL analysis.