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Mattermost EUVDEUVD-2026-77359

| CVE-2026-14259 MEDIUM
Missing Authorization (CWE-862)
2026-09-14 Mattermost GHSA-j89q-r2jw-jrj5
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:N/I:L/A:N
vuln.today AI
4.3 MEDIUM

Requires authenticated non-guest access (PR:L) over network; only outcome is unauthorized board creation (I:L) with no confidentiality or availability impact.

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

Primary rating from Vendor (Mattermost).

CVSS VectorVendor: Mattermost

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

Lifecycle Timeline

2
Metadata Corrected
Sep 14, 2026 - 11:40 vuln.today
tag: Authentication Bypass removed
Analysis Generated
Sep 14, 2026 - 11:25 vuln.today

DescriptionCVE.org

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to enforce board creation permissions when importing archive files which allows an authenticated non-guest team member to create Open or Private boards despite administrator restrictions via importing a crafted .boardarchive file. Mattermost Advisory ID: MMSA-2026-00712

AnalysisAI

Permission enforcement failure in Mattermost Boards allows authenticated non-guest team members to create Open or Private boards in defiance of administrator-imposed restrictions by importing a crafted .boardarchive file. The import code path omits the authorization check enforced by the direct board creation pathway, making administrative board creation controls bypassable by any authenticated non-guest user with import access. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Vulnerability AssessmentAI

Exploitation Requires a valid Mattermost account at non-guest team member level - guest accounts cannot exploit this. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The vendor-assigned and NVD-confirmed CVSS 3.1 score of 4.3 (Medium) with vector AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N accurately captures the constrained impact: network-reachable, low complexity, but requiring authenticated non-guest access (PR:L), with only low integrity impact and no confidentiality or availability consequences. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Upgrade to a patched release per the Mattermost security advisory MMSA-2026-00712 at https://mattermost.com/security-updates. … Detailed patch versions, workarounds, and compensating controls in full report.
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EUVD-2026-77359 vulnerability details – vuln.today
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