Remote username set to an arbitrary string by remote user
Priority LOW 20CWE-284Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Security bypass
- Confidentiality · integrity · availability
- None · Low · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-284.
Summary
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.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00338 27th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 9.10.0, 9.9.1, 9.5.7 +2github.com/mattermost/mattermost/server/v8 (Go): 9.5.7, 9.7.6, 9.8.2 +1
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Mattermost | Mattermost | 9.9.0; 9.5.0 – 9.5.6; 9.7.0 – 9.7.5; 9.8.0 – 9.8.1 | 9.10.0, 9.9.1, 9.5.7, 9.7.6, 9.8.2 | Patch available | CNA |
| — | github.com/mattermost/mattermost/server/v8 (Go) | 9.5.0 to before 9.5.7 | 9.5.7 | Patch available | GHSA-vg6q-84p8-qvqh |
| — | github.com/mattermost/mattermost/server/v8 (Go) | 9.7.0 to before 9.7.6 | 9.7.6 | Patch available | GHSA-vg6q-84p8-qvqh |
| — | github.com/mattermost/mattermost/server/v8 (Go) | 9.8.0 to before 9.8.2 | 9.8.2 | Patch available | GHSA-vg6q-84p8-qvqh |
| — | github.com/mattermost/mattermost/server/v8 (Go) | 9.9.0 to before 9.9.1 | 9.9.1 | Patch available | GHSA-vg6q-84p8-qvqh |
- Mattermost VendorMattermost Affected 9.9.0; 9.5.0 – 9.5.6; 9.7.0 – 9.7.5; 9.8.0 – 9.8.1 Fixed in 9.10.0, 9.9.1, 9.5.7, 9.7.6, 9.8.2 Patch available CNA
- github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected 9.5.0 to before 9.5.7 Fixed in 9.5.7 Patch available GHSA-vg6q-84p8-qvqh
- github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected 9.7.0 to before 9.7.6 Fixed in 9.7.6 Patch available GHSA-vg6q-84p8-qvqh
- github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected 9.8.0 to before 9.8.2 Fixed in 9.8.2 Patch available GHSA-vg6q-84p8-qvqh
- github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected 9.9.0 to before 9.9.1 Fixed in 9.9.1 Patch available GHSA-vg6q-84p8-qvqh
CPE configurations NVD · 2
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* | 9.5.0 to before 9.5.7; 9.7.0 to before 9.7.6; 9.8.0 to before 9.8.2 | Vulnerable | Mattermost |
| cpe:2.3:a:mattermost:mattermost_server:9.9.0:*:*:*:*:*:*:* | 9.9.0 | Vulnerable | Mattermost |
- cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* Versions 9.5.0 to before 9.5.7; 9.7.0 to before 9.7.6; 9.8.0 to before 9.8.2 Vulnerable ·Mattermost
- cpe:2.3:a:mattermost:mattermost_server:9.9.0:*:*:*:*:*:*:* Versions 9.9.0 Vulnerable ·Mattermost
Remediation
- Fix · CNA Mattermost (Mattermost) Fixed in 9.10.0, 9.9.1, 9.5.7, 9.7.6, 9.8.2
- Fix · GHSA-vg6q-84p8-qvqh github.com/mattermost/mattermost/server/v8 (Go) Fixed in 9.5.7 Advisory →
- Fix · GHSA-vg6q-84p8-qvqh github.com/mattermost/mattermost/server/v8 (Go) Fixed in 9.7.6 Advisory →
- Fix · GHSA-vg6q-84p8-qvqh github.com/mattermost/mattermost/server/v8 (Go) Fixed in 9.8.2 Advisory →
- Fix · GHSA-vg6q-84p8-qvqh github.com/mattermost/mattermost/server/v8 (Go) Fixed in 9.9.1 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2024-39839
- 2026-10-03 Alias added: GHSA-vg6q-84p8-qvqh
References
More Mattermost Server vulnerabilities
- TI-2025-18933 Arbitrary file read in Mattermost Boards via import & export board archive CVSS 3.1CRITICAL 9.9
- TI-2025-04465 Path Traversal Leading to RCE by Any Authenticated Mattermost User CVSS 3.1CRITICAL 9.9
- TI-2017-14068 An issue was discovered in Mattermost Server before 3.6.2. CVSS 3.1CRITICAL 9.8
- TI-2017-14060 An issue was discovered in Mattermost Server before 3.8.2, 3.7.5, and 3.6.7. CVSS 3.1CRITICAL 9.8
- TI-2017-14048 An issue was discovered in Mattermost Server before 4.1.0, 4.0.4, and 3.10.3. CVSS 3.1CRITICAL 9.8
- TI-2025-14360 Arbitrary file read via block duplication in Mattermost Boards CVSS 3.1CRITICAL 9.9
Sources
- CVE-2024-39839 · CVE Program
- CVE-2024-39839 · NVD
- FIRST EPSS
- GHSA-vg6q-84p8-qvqh · GitHub Advisory Database · CC BY 4.0
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