{"id":"CVE-2026-43969","aliases":["EEF-CVE-2026-43969","GHSA-g2wm-735q-3f56"],"url":"https://o3.security/vulnerability/CVE-2026-43969","summary":"Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1","details":"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.\n\ncow_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.\n\nThis issue affects cowlib from 2.9.0.","published":"2026-05-11T18:06:40.667Z","modified":"2026-08-07T11:49:57.579978125Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Hex","name":"cowlib","fixedVersion":null}],"fix":{"url":"https://github.com/erlef/cowlib/commit/177953dd51540da11090666c1f007214127a1144","label":"erlef/cowlib@177953d"},"references":[{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-43969"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://cna.erlef.org/cves/CVE-2026-43969.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43969.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-43969"},{"type":"FIX","url":"https://github.com/erlef/cowlib/commit/177953dd51540da11090666c1f007214127a1144"},{"type":"PACKAGE","url":"https://github.com/ninenines/cowlib"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T11:49:57.579978125Z"}}