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Mattermost CVE-2026-16048

| EUVDEUVD-2026-60206 MEDIUM
Incorrect Authorization (CWE-863)
2026-08-17 responsibledisclosure@mattermost.com GHSA-v37p-g38w-w7wg
Mattermost Authentication Bypass Mattermost Server
6.3
CVSS 3.1 · Vendor: mattermost
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Severity by source

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

Channel administrator role required (PR:L), API is network-accessible (AV:N); no availability impact identified from role reassignment within unchanged channel scope.

3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/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
Low
Integrity
Low
Availability
Low

Lifecycle Timeline

1
Analysis Generated
Aug 17, 2026 - 15:35 vuln.today

DescriptionCVE.org

Mattermost versions 11.8.x <= 11.8.2, 11.7.x <= 11.7.6, 10.11.x <= 10.11.21 fail to restrict channel member role assignment to channel-scoped roles which allows a channel administrator to gain additional channel permissions via the channel member roles API.. Mattermost Advisory ID: MMSA-2026-00697

AnalysisAI

Privilege escalation in Mattermost's channel administration API allows authenticated channel administrators to assign non-channel-scoped roles to channel members, exceeding their intended authorization boundary. Three active release lines are affected: 10.11.x through 10.11.21, 11.7.x through 11.7.6, and 11.8.x through 11.8.2. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Vulnerability AssessmentAI

Exploitation Exploitation requires an authenticated Mattermost account with the channel administrator role assigned within at least one channel - corresponding to PR:L in the CVSS vector. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 6.3 Medium score (AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L) reflects a network-accessible, low-complexity attack requiring only channel administrator authentication, with limited CIA impact confined to the channel scope - a reasonable assessment for an intra-platform privilege escalation. … 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 Mattermost release per vendor advisory MMSA-2026-00697, available at https://mattermost.com/security-updates; specific fixed version numbers are not independently confirmed from the available data beyond the affected ranges, so administrators should consult the advisory directly to identify the minimum safe version for their release line. … Detailed patch versions, workarounds, and compensating controls in full report.
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CVE-2026-16048 vulnerability details – vuln.today
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