{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "2.9.0"
              },
              {
                "last_affected": "2.9.0"
              }
            ],
            "source": [
              "AFFECTED_FIELD",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "04ca4c5d31a92d4d3de087bbd7d6021dc4a6d409"
            },
            {
              "fixed": "f77cb9b5e730e300fffb551db1ba5d1c4ed878ef"
            }
          ],
          "repo": "https://github.com/ninenines/cowboy",
          "type": "GIT"
        },
        {
          "database_specific": {
            "source": "REFERENCES"
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4f35609eb37109b106a863fc9ba83d7ee64e3e42"
            }
          ],
          "repo": "https://github.com/ninenines/gun",
          "type": "GIT"
        }
      ],
      "versions": [
        "2.9.0"
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "EEF",
    "cwe_ids": [
      "CWE-113"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43966.json",
    "unresolved_ranges": [
      {
        "extracted_events": [
          {
            "introduced": "a8b793db3d6ffe91d62f81baf41b1dab4cd78fb6"
          },
          {
            "last_affected": "a8b793db3d6ffe91d62f81baf41b1dab4cd78fb6"
          }
        ],
        "source": "AFFECTED_FIELD"
      }
    ]
  },
  "details": "Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') vulnerability in ninenines cowlib allows HTTP response splitting via non-VCHAR bytes in structured-fields string values.\n\ncow_http_struct_hd:escape_string/2 in cowlib only escapes \\ and \", passing all other bytes through verbatim. This creates an encoder/decoder asymmetry: the matching parser accepts only printable ASCII (0x20–0x7E, excluding \" and \\), but the encoder emits any byte including CR and LF. An application that builds a structured HTTP header via cow_http_struct_hd:item/1 (or a higher-level wrapper such as cow_http_hd:wt_protocol/1) from attacker-controlled input can have \\r\\n injected into the serialized header value. Once on the wire, the injected CRLF terminates the current header and any following bytes are interpreted as a new header, enabling HTTP response splitting.\n\nThis issue affects cowlib from 2.9.0.",
  "id": "CVE-2026-43966",
  "modified": "2026-07-08T05:38:06.174904997Z",
  "published": "2026-06-08T16:34:33.364Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com"
    },
    {
      "type": "WEB",
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-43966"
    },
    {
      "type": "WEB",
      "url": "https://repo.hex.pm"
    },
    {
      "type": "ADVISORY",
      "url": "https://cna.erlef.org/cves/CVE-2026-43966.html"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43966.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-43966"
    },
    {
      "type": "FIX",
      "url": "https://github.com/ninenines/cowboy/commit/f77cb9b5e730e300fffb551db1ba5d1c4ed878ef"
    },
    {
      "type": "FIX",
      "url": "https://github.com/ninenines/gun/commit/4f35609eb37109b106a863fc9ba83d7ee64e3e42"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/ninenines/cowlib"
    }
  ],
  "schema_version": "1.7.5",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "HTTP Response Splitting via Non-VCHAR Bytes in cow_http_struct_hd:escape_string/2"
}