Mattermost allows external websites to open within the app, exposing preload functionality to non-trusted sites.
Priority LOW 20CWE-829Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- Required
- Attack complexity
- Low
- Impact type
- Code execution
- Confidentiality · integrity · availability
- Low · Low · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-829.
Summary
Mattermost Desktop App versions <=5.13.3 fail to attach listeners restricting navigation to external sites within the Mattermost app which allows a malicious server to expose preload script functionality to untrusted servers via having a user open an external link in their Mattermost server. Mattermost Advisory ID: MMSA-2026-00596
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00162 5th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 5.13.4.0
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 5.13.3 | 5.13.4.0 | Patch available | CNA |
- Mattermost VendorMattermost Affected up to 5.13.3 Fixed in 5.13.4.0 Patch available CNA
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:mattermost:mattermost_desktop:*:*:*:*:*:*:*:* | before 5.13.4 | Vulnerable | Mattermost |
- cpe:2.3:a:mattermost:mattermost_desktop:*:*:*:*:*:*:*:* Versions before 5.13.4 Vulnerable ·Mattermost
Remediation
- Fix · CNA Mattermost (Mattermost) Fixed in 5.13.4.0
Timeline
- 2026-10-02 Threatist record created from CVE-2026-1628
- 2026-10-03 Alias added: GHSA-4q28-37qp-xh4g
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-2026-05712 Mattermost Desktop App fails to restrict the allow list of domains which NTLM credentials are passed CVSS 3.1HIGH 7.7
- TI-2026-00781 Arbitrary application execution via unvalidated server-controlled URLs in Help menu CVSS 3.1HIGH 7.6
Sources
- CVE-2026-1628 · CVE Program
- CVE-2026-1628 · NVD
- FIRST EPSS
- GHSA-4q28-37qp-xh4g · GitHub Advisory Database · CC BY 4.0
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