{"id":"CVE-2026-43966","summary":"HTTP Response Splitting via Non-VCHAR Bytes in cow_http_struct_hd:escape_string/2","details":"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 before 2.22.0.","aliases":["EEF-CVE-2026-43966","GHSA-w4f7-4cxr-rv3c"],"modified":"2026-11-10T02:45:37.875872867Z","published":"2026-06-08T16:34:33.364Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43966.json","cna_assigner":"EEF","cwe_ids":["CWE-113"]},"references":[{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-43966"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://cna.erlef.org/cves/CVE-2026-43966.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43966.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-43966"},{"type":"FIX","url":"https://github.com/ninenines/cowboy/commit/f77cb9b5e730e300fffb551db1ba5d1c4ed878ef"},{"type":"FIX","url":"https://github.com/ninenines/cowlib/commit/4401b858f2229abb3ea115c60924f6c77e5f8aa3"},{"type":"FIX","url":"https://github.com/ninenines/cowlib/commit/a8b793db3d6ffe91d62f81baf41b1dab4cd78fb6"},{"type":"FIX","url":"https://github.com/ninenines/gun/commit/4f35609eb37109b106a863fc9ba83d7ee64e3e42"},{"type":"PACKAGE","url":"https://github.com/ninenines/cowlib"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/ninenines/cowboy","events":[{"introduced":"0"},{"fixed":"f77cb9b5e730e300fffb551db1ba5d1c4ed878ef"}],"database_specific":{"extracted_events":[{"source":"REFERENCES_COMMIT","range":[{"fixed":"f77cb9b5e730e300fffb551db1ba5d1c4ed878ef"}]}]}},{"type":"GIT","repo":"https://github.com/ninenines/cowlib","events":[{"introduced":"b34155f725245848dca3a505398e262b1d50f25b"},{"fixed":"aca0ad953417b29bab2c41eeb4c37c98606c848b"},{"fixed":"4401b858f2229abb3ea115c60924f6c77e5f8aa3"},{"fixed":"a8b793db3d6ffe91d62f81baf41b1dab4cd78fb6"}],"database_specific":{"extracted_events":[{"cpe":"cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*","range":[{"introduced":"2.9.0"},{"fixed":"2.16.0"}],"source":"CPE_RANGE"},{"source":"REFERENCES_COMMIT","range":[{"fixed":"4401b858f2229abb3ea115c60924f6c77e5f8aa3"}]},{"range":[{"fixed":"a8b793db3d6ffe91d62f81baf41b1dab4cd78fb6"}],"source":"REFERENCES_COMMIT"}]}},{"type":"GIT","repo":"https://github.com/ninenines/gun","events":[{"introduced":"0"},{"fixed":"4f35609eb37109b106a863fc9ba83d7ee64e3e42"}],"database_specific":{"extracted_events":[{"source":"REFERENCES_COMMIT","range":[{"fixed":"4f35609eb37109b106a863fc9ba83d7ee64e3e42"}]}]}}],"versions":["2.15.0","2.14.2","2.14.1","2.14.0","2.13.0","2.12.0","2.11.0","2.10.0","2.9.0","2.8.0","2.7.0","2.6.3","2.6.2","2.6.1","2.6.0","2.5.0","2.4.0","2.3.0","2.2.2","2.2.1","2.2.0","2.1.0","2.0.0","2.0.0-rc.4","2.0.0-rc.3","2.0.0-rc.2","2.0.0-rc.1","2.0.0-pre.10","2.0.0-pre.9","2.0.0-pre.8","2.0.0-pre.7","2.0.0-pre.6","2.0.0-pre.5","2.0.0-pre.4","2.0.0-pre.3","2.0.0-pre.2","2.0.0-pre.1","1.0.0","0.10.0","0.9.0","0.8.6","0.8.5","0.8.4","0.8.3","0.8.2","0.8.1","0.8.0","0.6.1","0.6.0","0.4.0","0.2.0","2.12.1","2.10.1","2.9.1","2.0.1","1.3.0","1.2.0","1.1.0","1.0.0-rc.1","1.0.0-pre.5","1.0.0-pre.4","1.0.0-pre.3","1.0.0-pre.2","1.0.0-pre.1"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-43966.json"}}],"schema_version":"1.9.2","severity":[{"type":"CVSS_V4","score":"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"}]}