{"id":"CVE-2026-18799","aliases":["EUVD-2026-102751","GHSA-f4q7-3g3r-qrg8"],"status":"published","title":"Mattermost Server fails to restrict Slack import account binding, allowing team admins to forge posts as existing users","description":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail to restrict Slack import account binding to system administrator-initiated imports which allows an authenticated attacker with team admin privileges to force-add existing Mattermost users to their team and forge posts attributed to those users' identities via a crafted Slack export containing target users' email addresses.. Mattermost Advisory ID: MMSA-2026-00757","severity":{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.00198,"percentile":0.09683,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-862"],"published":"2026-10-16T07:16:19Z","modified":"2026-10-31T02:49:01Z","products":[{"vendor":"mattermost","product":"mattermost"},{"vendor":"mattermost","product":"mattermost_server"}],"references":[{"url":"https://mattermost.com/security-updates","tags":["vendor-advisory","Vendor Advisory","advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-18799","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-f4q7-3g3r-qrg8"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/18xxx/CVE-2026-18799.json","tags":["advisory"]}],"sources":{"cve":[{"id":"CVE-2026-18799","title":"Mattermost Server fails to restrict Slack import account binding, allowing team admins to forge posts as existing users","description":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail to restrict Slack import account binding to system administrator-initiated imports which allows an authenticated attacker with team admin privileges to force-add existing Mattermost users to their team and forge posts attributed to those users' identities via a crafted Slack export containing target users' email addresses.. Mattermost Advisory ID: MMSA-2026-00757","status":"published","published":"2026-10-16T07:16:19.062Z","modified":"2026-10-16T11:28:45.2Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-862"],"updated_at":"2026-11-02T14:20:12.939084Z"}],"euvd":[{"id":"EUVD-2026-102751","description":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail to restrict Slack import account binding to system administrator-initiated imports which allows an authenticated attacker with team admin privileges to force-add existing Mattermost users to their team and forge posts attributed to those users' identities via a crafted Slack export containing target users' email addresses.. Mattermost Advisory ID: MMSA-2026-00757","status":"published","published":"2026-10-16T07:16:19Z","modified":"2026-10-16T11:28:45Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T17:00:06.711534Z"}],"ghsa":[{"id":"GHSA-f4q7-3g3r-qrg8","title":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail...","description":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail to restrict Slack import account binding to system administrator-initiated imports which allows an authenticated attacker with team admin privileges to force-add existing Mattermost users to their team and forge posts attributed to those users' identities via a crafted Slack export containing target users' email addresses.. Mattermost Advisory ID: MMSA-2026-00757","status":"published","published":"2026-10-16T09:30:29Z","modified":"2026-10-16T09:30:38Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N","level":"medium"}],"cwes":["CWE-862"],"updated_at":"2026-11-02T15:13:51.12467Z"}],"nvd":[{"id":"CVE-2026-18799","description":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail to restrict Slack import account binding to system administrator-initiated imports which allows an authenticated attacker with team admin privileges to force-add existing Mattermost users to their team and forge posts attributed to those users' identities via a crafted Slack export containing target users' email addresses.. Mattermost Advisory ID: MMSA-2026-00757","status":"published","published":"2026-10-16T08:17:13.073Z","modified":"2026-10-29T18:08:12.137Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N","level":"medium","assessor":"secondary"}],"cwes":["CWE-862"],"updated_at":"2026-11-02T14:12:59.751798Z"}],"osv":[{"id":"CVE-2026-18799","title":"Mattermost Server fails to restrict Slack import account binding, allowing team admins to forge posts as existing users","description":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail to restrict Slack import account binding to system administrator-initiated imports which allows an authenticated attacker with team admin privileges to force-add existing Mattermost users to their team and forge posts attributed to those users' identities via a crafted Slack export containing target users' email addresses.. Mattermost Advisory ID: MMSA-2026-00757","status":"published","published":"2026-10-16T07:16:19.062Z","modified":"2026-10-31T02:49:01.025062578Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N","level":"medium"}],"cwes":["CWE-862"],"updated_at":"2026-11-02T15:44:58.024074Z"}]}}