{"cve":"CVE-2026-43966","nvd":{"published":"2026-06-08T17:16:43.447","modified":"2026-10-14T10:17:53.653","status":"Modified","description":"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 onward.","cvss_v4":{"vector":"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","score":6.3},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","score":5.3},"cwes":["CWE-113"],"references":["https://cna.erlef.org/cves/CVE-2026-43966.html","https://github.com/ninenines/cowboy/commit/f77cb9b5e730e300fffb551db1ba5d1c4ed878ef","https://github.com/ninenines/cowlib/commit/4401b858f2229abb3ea115c60924f6c77e5f8aa3","https://github.com/ninenines/cowlib/commit/a8b793db3d6ffe91d62f81baf41b1dab4cd78fb6","https://github.com/ninenines/gun/commit/4f35609eb37109b106a863fc9ba83d7ee64e3e42"],"products":["ninenines:cowlib"],"source":"nvd","synced_at":"2026-10-19T22:38:48.522727527+00:00"},"epss":{"cve":"CVE-2026-43966","score":0.00259,"percentile":0.17385,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}