gun HTTP/1.1 client accepts unsolicited 101 Switching Protocols response allowing server-driven protocol hijack and OOM_CVE-2026-43974

{
    "lastseen": "",
    "description": "Unexpected Status Code or Return Value vulnerability in ninenines gun (gun_http module) allows a malicious HTTP server to force the client into raw protocol mode via an unsolicited 101 Switching Protocols response.\n\nIn gun_http:handle_inform/8, when a 101 Switching Protocols response is received over HTTP/1.1, the function verifies only that the Upgrade header is syntactically valid and that the stream reference is a plain reference(). It does not check whether the client ever sent an Upgrade or Connection: upgrade header on the corresponding request. Because this check is absent, any 101 response (solicited or not) causes gun to dispatch a gun_upgrade message to the caller and transition the entire connection to raw protocol mode.\n\nA malicious or compromised HTTP server can send an unsolicited 101 response to any HTTP/1.1 request, causing the gun client to abandon HTTP framing for that connection. Once in raw mode, gun_raw applies no flow control (flow=infinity) and re-arms socket active mode after every received packet, so the server can flood the client with arbitrary bytes. These are forwarded as unbounded gun_data messages to the owner process, exhausting its mailbox and BEAM memory, ultimately crashing the VM.\n\nThis issue affects gun: from 2.0.0 before 2.4.0.",
    "published": "2026-06-08T14:12:36.957Z",
    "modified": "2026-06-08T14:15:51.636Z",
    "type": "cve",
    "title": "gun HTTP/1.1 client accepts unsolicited 101 Switching Protocols response allowing server-driven protocol hijack and OOM",
    "source": "EEF",
    "references": "https://cna.erlef.org/cves/CVE-2026-43974.html\nhttps://osv.dev/vulnerability/EEF-CVE-2026-43974\nhttps://github.com/ninenines/gun/commit/5b48068c29ce5e112cb149b5857c7d4dc319a81b",
    "id": "CVE-2026-43974",
    "bulletinFamily": "",
    "cwe": [
        "CWE-841"
    ],
    "cvelist": null,
    "sourceData": "ninenines gun 2.0.0\nninenines gun a3c2edbb8c807717e2f10520c6cf1e77a62eab2e",
    "sourceHref": "",
    "cvss": {
        "score": 8.7,
        "severity": "HIGH",
        "vector": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
        "version": "4.0"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
            "attackVector": "",
            "attackComplexity": "",
            "privilegesRequired": "",
            "userInteraction": "",
            "scope": "",
            "confidentialityImpact": "",
            "integrityImpact": "",
            "availabilityImpact": ""
        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "gun",
    "version": "2.0.0",
    "vendor": "ninenines",
    "ai_description": "Unexpected Status Code or Return Value vulnerability in ninenines gun (gun_http module) allows a malicious HTTP server to force the client into raw protocol mode via an unsolicited 101 Switching Protocols response.",
    "ai_severity": "High",
    "ai_vendor": "ninenines",
    "ai_product": "gun",
    "ai_version": "2.0.0-2.3.0",
    "ai_score": 8.7
}