{"id":"EEF-CVE-2026-43969","summary":"Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1","details":"## Summary\n\nImproper 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\n`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.\n\nThis issue affects cowlib: from 2.9.0 onward.\n\n## Workarounds\n\nValidate 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.\n\n## Configurations\n\nThe 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.","aliases":["CVE-2026-43969","GHSA-g2wm-735q-3f56"],"modified":"2026-09-09T14:30:03.772617250Z","published":"2026-05-11T18:06:40.667Z","database_specific":{"cwe_ids":["CWE-93"],"capec_ids":["CAPEC-105"],"cpe_ids":["cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*"]},"references":[{"type":"FIX","url":"https://github.com/erlef/cowlib/commit/177953dd51540da11090666c1f007214127a1144"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-43969.html"},{"type":"PACKAGE","url":"https://hex.pm/packages/cowlib"}],"affected":[{"package":{"name":"cowlib","ecosystem":"Hex","purl":"pkg:hex/cowlib"},"ranges":[{"type":"SEMVER","events":[{"introduced":"2.9.0"}]}],"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":[{"type":"GIT","repo":"https://github.com/ninenines/cowlib","events":[{"introduced":"f017f8a0ecbffd5033d9ab49bf180186f7a523a7"}]}],"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"}}],"schema_version":"1.9.0","severity":[{"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"}],"credits":[{"name":"Peter Ullrich","type":"FINDER"}]}