Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1

{
  "id": "a4df59f85d163514b3fc0f70eea1f143d4dba120d072ec7fa59bbb8a8c60c42f",
  "url": "https://osv.dev/vulnerability/EEF-CVE-2026-43969",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1",
    "summary": "## Summary Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in ninenines cowlib allows HTTP request splitting and cookie smuggling via unvalidated cookie name and value fields. `cow_cookie:cookie/1` in cowlib builds a client-side `Cookie:` request header from a list of name-value pairs without validating either field. An attacker who controls the cookie names or values passed to this function can inject `;`, `,`, CR, LF, or TAB characters into the serialized header. This enables two classes of attack: cookie smuggling within a single header (e.g. injecting `; admin=1` to introduce a phantom cookie that the receiving server treats as authentic) and HTTP request header splitting (injecting CRLF to append arbitrary headers or smuggle a complete second request against a shared upstream proxy). The decoder side (`parse_cookie_name/1`, `parse_cookie_value/1`) and `setcookie/3` already validate and reject these characters; the encoder alone is missing the check. This issue affects cowlib: from 2.9.0 before 2.21.0. ## Workarounds Validate inputs into `cow_cookie:cookie/1` to only include valid cookie name and value characters as defined in RFC 6265 Section 4.1.1 before passing them to the function. ## Configurations The application must pass attacker-controlled bytes as cookie names or values to `cow_cookie:cookie/1`. Applications that construct cookie lists exclusively from trusted, application-controlled values are not affected.",
    "evidence": "osv:EEF-CVE-2026-43969",
    "products": [
      {
        "name": {
          "value": "cowlib",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "2.21.0",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": [
          {
            "value": "2.10.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.10.1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.11.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.12.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.12.1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.13.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.14.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.15.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.16.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.16.1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.17.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.17.1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.18.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.19.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.20.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.9.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "2.9.1",
            "evidence": "/affected/0/versions"
          }
        ]
      }
    ],
    "severity": "low",
    "structured": {
      "id": "EEF-CVE-2026-43969",
      "aliases": [
        "CVE-2026-43969",
        "EEF-CVE-2026-43969",
        "GHSA-g2wm-735q-3f56"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "2.9.0"
                },
                {
                  "fixed": "2.21.0"
                }
              ]
            }
          ],
          "package": {
            "name": "cowlib",
            "purl": "pkg:hex/cowlib",
            "ecosystem": "Hex"
          },
          "versions": [
            "2.10.0",
            "2.10.1",
            "2.11.0",
            "2.12.0",
            "2.12.1",
            "2.13.0",
            "2.14.0",
            "2.15.0",
            "2.16.0",
            "2.16.1",
            "2.17.0",
            "2.17.1",
            "2.18.0",
            "2.19.0",
            "2.20.0",
            "2.9.0",
            "2.9.1"
          ],
          "database_specific": {
            "source": "https://cna.erlef.org/osv/EEF-CVE-2026-43969.json"
          }
        },
        {
          "ranges": [
            {
              "repo": "https://github.com/ninenines/cowlib",
              "type": "GIT",
              "events": [
                {
                  "introduced": "f017f8a0ecbffd5033d9ab49bf180186f7a523a7"
                },
                {
                  "fixed": "c17fd73945ef536cccecc492d286fb6b6d1c3307"
                }
              ]
            }
          ],
          "versions": [
            "2.20.0",
            "2.19.0",
            "2.18.0",
            "2.17.1",
            "2.17.0",
            "2.16.1",
            "2.16.0",
            "2.15.0",
            "2.14.0",
            "2.13.0",
            "2.12.1",
            "2.12.0",
            "2.11.0",
            "2.10.1",
            "2.10.0",
            "2.9.1",
            "2.9.0"
          ],
          "database_specific": {
            "source": "https://cna.erlef.org/osv/EEF-CVE-2026-43969.json"
          }
        }
      ],
      "modified": "2026-10-09T07:00:03.523201772Z",
      "provider": "osv",
      "references": [
        "https://github.com/erlef/cowlib/commit/177953dd51540da11090666c1f007214127a1144",
        "https://cna.erlef.org/cves/CVE-2026-43969.html",
        "https://github.com/ninenines/cowlib/commit/f017f8a0ecbffd5033d9ab49bf180186f7a523a7",
        "https://github.com/ninenines/cowlib/commit/c17fd73945ef536cccecc492d286fb6b6d1c3307",
        "https://hex.pm/packages/cowlib"
      ],
      "provider_metadata": {
        "cpe_ids": [
          "cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*"
        ],
        "cwe_ids": [
          "CWE-93"
        ],
        "capec_ids": [
          "CAPEC-105"
        ]
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-43969",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 108720,
  "published_at": "2026-05-11T18:06:40.667+00:00"
}