SSRF via unvalidated attachment URLs in Mattermost Agents plugin MCP server
Published Jun 26, 2026
6.5
MEDIUMCVSS 3.1
EPSS 0.14%
Description
Mattermost versions 10.11.x <= 10.11.18, 11.6.x <= 11.6.3, 11.5.x <= 11.5.6 fail to validate attachment URLs against internal or private IP ranges in the Mattermost Agents plugin MCP server which allows an attacker with access to the MCP server in stdio mode to perform server-side request forgery (SSRF) and exfiltrate data from internal network services via supplying internal URLs as file attachments in post creation requests.. Mattermost Advisory ID: MMSA-2026-00635
Affected products
-
- Version 10.11.0StatusaffectedConstraints<=10.11.18
- Version 11.5.0StatusaffectedConstraints<=11.5.6
- Version 11.6.0StatusaffectedConstraints<=11.6.3
- Version 10.11.19StatusunaffectedConstraints-
- Version 11.5.7StatusunaffectedConstraints-
- Version 11.6.4StatusunaffectedConstraints-
- Version 11.7.0StatusunaffectedConstraints-
- Version
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Mattermost | Mattermost | unaffected |
|
- ≥ 10.11.0 · < 10.11.19
- ≥ 11.5.0 · < 11.5.7
- ≥ 11.6.0 · < 11.6.4
No data.
No Red Hat product state for this CVE.
No package ranges for this CVE.
Remediation
Vendor solution
Update Mattermost to versions 11.7.0, 10.11.19, 11.6.4, 11.5.7 or higher.
References (1)
- https://mattermost.com/security-updates vendor-advisoryVendor Advisory
| Link | Providers | Tags |
|---|---|---|
| https://mattermost.com/security-updates | vendor-advisoryVendor Advisory |
Change history (0)
No recorded changes yet.