{"id":"CVE-2026-43969","aliases":["AZL-86787","EEF-CVE-2026-43969","EUVD-2026-29193","GHSA-g2wm-735q-3f56"],"status":"published","title":"Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1","description":"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 before 2.21.0.","severity":{"version":"4.0","score":2.1,"vector":"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","level":"low","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.00147,"percentile":0.03968,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-93"],"published":"2026-05-11T18:06:40Z","modified":"2026-11-05T05:40:51Z","fixes":[{"ecosystem":"Azure Linux:3","package":"rabbitmq-server","fixed_in":["3.13.7-10"],"sources":["osv"]},{"ecosystem":"Hex","package":"cowlib","fixed_in":["2.21.0"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"Hex","package":"cowlib","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.9.0"},{"last_affected":"2.16.1"}]}]},{"source":"osv","ecosystem":"Azure Linux:3","package":"rabbitmq-server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.13.7-10"}]}]},{"source":"osv","ecosystem":"Hex","package":"cowlib","ranges":[{"type":"SEMVER","events":[{"introduced":"2.9.0"},{"fixed":"2.21.0"}]}],"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"]},{"source":"osv","ecosystem":"Hex","package":"cowlib","ranges":[{"type":"SEMVER","events":[{"introduced":"2.9.0"},{"last_affected":"2.16.1"}]}],"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","2.9.0","2.9.1"]}],"products":[{"vendor":"ninenines","product":"cowlib"}],"references":[{"url":"https://github.com/erlef/cowlib/commit/177953dd51540da11090666c1f007214127a1144","tags":["patch","Patch","fix","web"]},{"url":"https://cna.erlef.org/cves/CVE-2026-43969.html","tags":["related","third-party-advisory","Vendor Advisory","advisory","web"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-43969","tags":["related","Third Party Advisory","web"]},{"url":"https://github.com/ninenines/cowlib/commit/f017f8a0ecbffd5033d9ab49bf180186f7a523a7","tags":["related","fix","web"]},{"url":"https://github.com/ninenines/cowlib/commit/c17fd73945ef536cccecc492d286fb6b6d1c3307","tags":["patch","fix"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-43969","tags":["web","advisory"]},{"url":"https://github.com/advisories/GHSA-g2wm-735q-3f56"},{"url":"https://github.com","tags":["web"]},{"url":"https://repo.hex.pm","tags":["web"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43969.json","tags":["advisory"]},{"url":"https://github.com/ninenines/cowlib","tags":["package"]},{"url":"https://hex.pm/packages/cowlib","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-43969","title":"Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1","description":"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 before 2.21.0.","status":"published","published":"2026-05-11T18:06:40.667Z","modified":"2026-10-09T06:57:15.234Z","cvss":[{"version":"4.0","score":2.1,"vector":"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","level":"low","assessor":"cna"}],"cwes":["CWE-93"],"updated_at":"2026-11-02T13:37:25.103021Z"}],"euvd":[{"id":"EUVD-2026-29193","description":"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 before 2.21.0.","status":"published","published":"2026-05-11T18:06:40Z","modified":"2026-10-09T06:57:15Z","cvss":[{"version":"4.0","score":2.1,"vector":"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","level":"low"}],"updated_at":"2026-11-02T17:27:25.459601Z"}],"ghsa":[{"id":"GHSA-g2wm-735q-3f56","title":"cowlib: Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1","description":"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.","status":"published","published":"2026-05-11T21:31:34Z","modified":"2026-06-08T20:17:03Z","cvss":[{"version":"4.0","score":2.1,"vector":"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","level":"low"},{"version":"3.1","score":3.2,"vector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N","level":"low"}],"cwes":["CWE-93"],"updated_at":"2026-11-02T14:40:20.187636Z"}],"nvd":[{"id":"CVE-2026-43969","description":"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 before 2.21.0.","status":"published","published":"2026-05-11T19:16:25.33Z","modified":"2026-10-26T20:10:00.16Z","cvss":[{"version":"4.0","score":2.1,"vector":"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"low","assessor":"secondary"},{"version":"3.1","score":3.2,"vector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N","level":"low","assessor":"primary"}],"cwes":["CWE-93"],"updated_at":"2026-11-02T14:12:18.239974Z"}],"osv":[{"id":"CVE-2026-43969","title":"Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1","description":"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 before 2.21.0.","status":"published","published":"2026-05-11T18:06:40.667Z","modified":"2026-10-28T02:31:07.651402951Z","cvss":[{"version":"4.0","score":2.1,"vector":"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","level":"low"}],"cwes":["CWE-93"],"updated_at":"2026-11-02T15:45:04.820169Z"},{"id":"EEF-CVE-2026-43969","title":"Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1","description":"## 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 before 2.21.0.\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.","status":"published","published":"2026-05-11T18:06:40.667Z","modified":"2026-10-09T07:00:03.523201772Z","cvss":[{"version":"4.0","score":2.1,"vector":"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","level":"low"}],"cwes":["CWE-93"],"updated_at":"2026-11-02T15:46:33.047032Z"},{"id":"GHSA-g2wm-735q-3f56","title":"cowlib: Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1","description":"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.","status":"published","published":"2026-05-11T21:31:34Z","modified":"2026-06-08T20:31:01.091008738Z","cvss":[{"version":"3.1","score":3.2,"vector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N","level":"low"},{"version":"4.0","score":2.1,"vector":"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","level":"low"}],"cwes":["CWE-93"],"updated_at":"2026-11-02T15:46:47.119724Z"},{"id":"AZL-86787","title":"CVE-2026-43969 affecting package rabbitmq-server for versions less than 3.13.7-10","description":"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 before 2.21.0.","status":"published","published":"2026-05-11T19:16:25Z","modified":"2026-11-05T05:40:51Z","updated_at":"2026-11-05T16:41:25.190302Z"}]}}