Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server_CVE-2026-5740

{
    "lastseen": "",
    "description": "Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to properly validate msgpack-encoded WebSocket frames before memory allocation which allows an unauthenticated remote attacker to crash the server process and cause a full service outage for all users via a crafted binary WebSocket message sent to the public WebSocket endpoint.. Mattermost Advisory ID: MMSA-2026-00647",
    "published": "2026-05-22T10:22:01.030Z",
    "modified": "2026-05-22T12:14:25.145Z",
    "type": "cve",
    "title": "Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server",
    "source": "Mattermost",
    "references": "https://mattermost.com/security-updates",
    "id": "CVE-2026-5740",
    "bulletinFamily": "",
    "cwe": [
        "CWE-789"
    ],
    "cvelist": null,
    "sourceData": "Mattermost Mattermost 11.6.0\nMattermost Mattermost 11.5.0\nMattermost Mattermost 11.4.0\nMattermost Mattermost 10.11.0",
    "sourceHref": "",
    "cvss": {
        "score": 7.5,
        "severity": "HIGH",
        "vector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
        "version": "3.1"
    },
    "cvss2": [],
    "cvss3": {
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        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
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        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
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        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "Mattermost",
    "version": "11.6.0",
    "vendor": "Mattermost",
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    "ai_score": 0
}