CVE-2026-18795

Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to enforce DM/GM check on server side which allows an authenticated user to quarantine a post belonging to DM or GM via direct API call.. Mattermost Advisory ID: MMSA-2026-00756

CVSS v3 6.4 MEDIUM

6.4^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 1.6 / Impact : 4.7

Attack Vector NETWORK

Attack Complexity HIGH

Privileges Required LOW

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact LOW

Availability Impact LOW

Scope UNCHANGED

References

Link	Resource
https://mattermost.com/security-updates	Vendor Advisory

Configurations

Configuration 1 (hide)

OR	cpe:2.3:a:mattermost:mattermost_server::::::::
	cpe:2.3:a:mattermost:mattermost_server::::::::
	cpe:2.3:a:mattermost:mattermost_server::::::::
	cpe:2.3:a:mattermost:mattermost_server:11.10.0:::::::*

History

29 Oct 2026, 18:08

Type	Values Removed	Values Added
References	~~() https://mattermost.com/security-updates -~~	() https://mattermost.com/security-updates - Vendor Advisory
CPE		cpe:2.3:a:mattermost:mattermost_server:11.10.0:::::::* cpe:2.3:a:mattermost:mattermost_server::::::::
First Time		Mattermost mattermost Server Mattermost

16 Oct 2026, 07:17

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-10-16 07:17

Updated : 2026-10-29 18:08

NVD link : CVE-2026-18795

Mitre link : CVE-2026-18795

CVE.ORG link : CVE-2026-18795

JSON object : View

Products Affected

mattermost

mattermost_server

CWE

CWE-862

Missing Authorization

{"id": "CVE-2026-18795", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-18795", "role": "CISA Coordinator", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "version": "2.0.3", "timestamp": "2026-10-16T11:59:31.276508Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "responsibledisclosure@mattermost.com", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 6.4, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L", "integrityImpact": "LOW", "userInteraction": "NONE", "attackComplexity": "HIGH", "availabilityImpact": "LOW", "privilegesRequired": "LOW", "confidentialityImpact": "HIGH"}, "impactScore": 4.7, "exploitabilityScore": 1.6}]}, "affected": [{"source": "responsibledisclosure@mattermost.com", "affectedData": [{"vendor": "Mattermost", "product": "Mattermost", "versions": [{"status": "affected", "version": "11.10.0", "versionType": "semver", "lessThanOrEqual": "11.10.0"}, {"status": "affected", "version": "11.7.0", "versionType": "semver", "lessThanOrEqual": "11.7.9"}, {"status": "affected", "version": "11.9.0", "versionType": "semver", "lessThanOrEqual": "11.9.1"}, {"status": "affected", "version": "11.8.0", "versionType": "semver", "lessThanOrEqual": "11.8.5"}, {"status": "unaffected", "version": "11.11.0"}, {"status": "unaffected", "version": "11.10.1"}, {"status": "unaffected", "version": "11.7.10"}, {"status": "unaffected", "version": "11.9.2"}, {"status": "unaffected", "version": "11.8.6"}], "defaultStatus": "unaffected"}]}], "published": "2026-10-16T07:17:12.407", "references": [{"url": "https://mattermost.com/security-updates", "tags": ["Vendor Advisory"], "source": "responsibledisclosure@mattermost.com"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Secondary", "source": "responsibledisclosure@mattermost.com", "description": [{"lang": "en", "value": "CWE-862"}]}], "descriptions": [{"lang": "en", "value": "Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to enforce DM/GM check on server side which allows an authenticated user to quarantine a post belonging to DM or GM via direct API call.. Mattermost Advisory ID: MMSA-2026-00756"}], "lastModified": "2026-10-29T18:08:37.923", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "0D5A7979-C6DD-4EEA-B7C4-60C425EAD2C3", "versionEndExcluding": "11.7.10", "versionStartIncluding": "11.7.0"}, {"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "864932C7-FD92-48AC-8789-DF73D5CA9AAF", "versionEndExcluding": "11.8.6", "versionStartIncluding": "11.8.0"}, {"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "2F937268-2154-4B45-B9E0-8B3451070CD0", "versionEndExcluding": "11.9.2", "versionStartIncluding": "11.9.0"}, {"criteria": "cpe:2.3:a:mattermost:mattermost_server:11.10.0:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "C945CD83-FCEB-439D-8F18-02213CE7E7BF"}], "operator": "OR"}]}], "sourceIdentifier": "responsibledisclosure@mattermost.com"}