Mattermost Desktop App fails to restrict the allow list of domains which NTLM credentials are passed
Priority LOW 33CWE-522Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Information disclosure
- Confidentiality · integrity · availability
- High · None · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · NVD. Fix status from CNA. Impact type from CWE-522.
Summary
Mattermost Desktop App versions <=6.1 5.5.13.0 fail to restrict the allow list of domains to which NTLM credentials were forwarded to in the Mattermost Desktop App which allows any user on a server without the image proxy enabled to intercept other users credentials via embedding an image that routes to an external web server. Mattermost Advisory ID: MMSA-2026-00651
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00187 8th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 6.2.0, 5.13.6.0
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 | up to 5.5.13 | 6.2.0, 5.13.6.0 | Patch available | CNA |
- Mattermost VendorMattermost Affected up to 5.5.13 Fixed in 6.2.0, 5.13.6.0 Patch available CNA
CPE configurations NVD · 2
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:mattermost:mattermost_desktop:*:-:*:*:*:*:*:* | up to 5.13.0 | Vulnerable | Mattermost |
| cpe:2.3:a:mattermost:mattermost_desktop:*:*:*:*:*:*:*:* | 6.1.0 – 6.1.5 | Vulnerable | Mattermost |
- cpe:2.3:a:mattermost:mattermost_desktop:*:-:*:*:*:*:*:* Versions up to 5.13.0 Vulnerable ·Mattermost
- cpe:2.3:a:mattermost:mattermost_desktop:*:*:*:*:*:*:*:* Versions 6.1.0 – 6.1.5 Vulnerable ·Mattermost
Remediation
- Fix · CNA Mattermost (Mattermost) Fixed in 6.2.0, 5.13.6.0
Timeline
- 2026-10-02 Threatist record created from CVE-2026-6517
- 2026-10-03 Alias added: GHSA-2wmq-3m94-g4jr
References
Advisory 1
More Mattermost Desktop vulnerabilities
- TI-2019-15074 An issue was discovered in Mattermost Desktop App before 4.3.0 on macOS. CVSS 3.1CRITICAL 9.8
- TI-2016-09099 An issue was discovered in Mattermost Desktop App before 3.4.0. CVSS 3.1CRITICAL 9.8
- TI-2019-15079 An issue was discovered in Mattermost Desktop App before 4.2.2. CVSS 3.1HIGH 8.8
- TI-2024-26542 RCE in desktop app in Windows by local attacker CVSS 3.1HIGH 7.8
- TI-2026-00781 Arbitrary application execution via unvalidated server-controlled URLs in Help menu CVSS 3.1HIGH 7.6
- TI-2020-11317 An issue was discovered in Mattermost Desktop App before 4.4.0. CVSS 3.1HIGH 7.3
Sources
- CVE-2026-6517 · CVE Program
- CVE-2026-6517 · NVD
- FIRST EPSS
- GHSA-2wmq-3m94-g4jr · GitHub Advisory Database · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences