{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "2.0.0"
              },
              {
                "fixed": "2.4.0"
              }
            ],
            "source": [
              "DESCRIPTION",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "33223e751267c5f249f3db1277c13904a1801b92"
            },
            {
              "fixed": "8cc70ed78fc946e5d9c49e92d84bde64ca12db1f"
            },
            {
              "fixed": "5b48068c29ce5e112cb149b5857c7d4dc319a81b"
            }
          ],
          "repo": "https://github.com/ninenines/gun",
          "type": "GIT"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "EEF",
    "cwe_ids": [
      "CWE-841"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43974.json",
    "unresolved_ranges": [
      {
        "extracted_events": [
          {
            "introduced": "a3c2edbb8c807717e2f10520c6cf1e77a62eab2e"
          },
          {
            "fixed": "5b48068c29ce5e112cb149b5857c7d4dc319a81b"
          }
        ],
        "source": "AFFECTED_FIELD"
      }
    ]
  },
  "details": "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.",
  "id": "CVE-2026-43974",
  "modified": "2026-07-08T05:39:12.931046340Z",
  "published": "2026-06-08T14:12:36.957Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com"
    },
    {
      "type": "WEB",
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-43974"
    },
    {
      "type": "ADVISORY",
      "url": "https://cna.erlef.org/cves/CVE-2026-43974.html"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43974.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-43974"
    },
    {
      "type": "FIX",
      "url": "https://github.com/ninenines/gun/commit/5b48068c29ce5e112cb149b5857c7d4dc319a81b"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/ninenines/gun"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/ninenines/gun.git"
    }
  ],
  "schema_version": "1.7.5",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "gun HTTP/1.1 client accepts unsolicited 101 Switching Protocols response allowing server-driven protocol hijack and OOM"
}