{"id":"CVE-2026-4339","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-4339","generatedAt":"2026-10-27T23:56:36.542Z","title":"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…","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","published":"2026-06-26T15:16:40.000Z","lastModified":"2026-06-29T19:26:34.000Z","status":"Analyzed","sourceIdentifier":"responsibledisclosure@mattermost.com","cvss":{"version":"3.1","score":6.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N"},"cwe":["CWE-918"],"affected":["mattermost/mattermost server"],"epss":{"score":0.00139,"percentile":0.03231,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and a low EPSS score (0.14%). Track it; it rarely justifies an emergency change on its own."},"changes":[],"references":[{"url":"https://mattermost.com/security-updates","tags":["Vendor Advisory"],"source":"responsibledisclosure@mattermost.com"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-4339","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}