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    CVE-2026-5163

    Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite endpoint.. Mattermost Advisory ID: MMSA-2026-00645

    Published:May 18, 2026
    Last Modified:May 18, 2026
    EPS:May 18, 2026
    EPSS Score:
    CVSS Score:6.5

    Affected Products

    Vendor
    Mattermost
    Product
    Mattermost
    Vendor
    Mattermost
    Product
    Mattermost Server

    Exploits

    No exploit reference

    Common Weakness Enumeration

    CWE-862 Missing Authorization

    Common Attack Pattern Enumeration and Classification (CAPEC)

    CAPEC-665 Exploitation of Thunderbolt Protection Flaws

    Related CVEs

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    CVE-2026-10080 (CVSS 6.5) — Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fails to validate WebSocket comman…
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    CVE-2026-15754 (CVSS 4.2) — Mattermost versions 11.7.x <= 11.7.6, 11.8.x <= 11.8.3 The access control policy unassign endpoint fails to re…
    CVE-2026-16044 (CVSS 5.4) — Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21 fail to prevent guest users from receiving Board Adm…
    CVE-2026-16045 (CVSS 4.3) — Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21 Mattermost failed to restrict OAuth deauthorization …
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    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High