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Mattermost CVE-2026-9824

| EUVDEUVD-2026-43339 MEDIUM
Missing Authorization (CWE-862)
2026-07-13 Mattermost
Authentication Bypass Mattermost
4.3
CVSS 3.1 · Vendor: Mattermost
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Severity by source

Vendor (Mattermost) PRIMARY
4.3 MEDIUM
AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
vuln.today AI
4.3 MEDIUM

Network-reachable via standard Mattermost client; requires authenticated session (PR:L); only remote cluster metadata disclosed, so C:L with no integrity or availability impact.

3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (Mattermost).

CVSS VectorVendor: Mattermost

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

Lifecycle Timeline

1
Analysis Generated
Jul 13, 2026 - 11:30 vuln.today

DescriptionCVE.org

Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to check the manage_shared_channels permission in the /share-channel autocomplete handler, which allows an authenticated user without that permission to enumerate configured remote cluster connection metadata via slash command autocomplete.. Mattermost Advisory ID: MMSA-2026-00676

AnalysisAI

Missing authorization in Mattermost's /share-channel slash command autocomplete handler allows any authenticated user to enumerate remote cluster connection metadata, regardless of whether they hold the manage_shared_channels permission. Affects three active release lines (11.7.x, 11.6.x, 10.11.x) and is classified under CWE-862 (Missing Authorization). …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Authenticate with any valid Mattermost account
Delivery
Type /share-channel in message input
Exploit
Trigger autocomplete handler without permission check
Execution
Receive remote cluster connection metadata
Impact
Map federation topology for reconnaissance
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Vulnerability AssessmentAI

Exploitation Exploitation requires a valid, authenticated Mattermost user account (PR:L per CVSS vector) - unauthenticated access is not sufficient. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The NVD-assigned CVSS base score of 4.3 (Medium) accurately reflects the constrained real-world impact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An authenticated Mattermost user with no special permissions opens any channel, types /share-channel into the message input box, and observes the autocomplete suggestions returned by the server. The autocomplete response includes remote cluster connection metadata - such as cluster display names, identifiers, or hostnames - that the user should not be permitted to see. …
Remediation Patch available per vendor advisory. … Detailed patch versions, workarounds, and compensating controls in full report.
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CVE-2026-9824 vulnerability details – vuln.today
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