{"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.","aliases":["EEF-CVE-2026-43966"],"modified":"2026-07-08T08:05:14.330550698Z","published":"2026-06-08T16:34:33.364Z","database_specific":{"cna_assigner":"EEF","unresolved_ranges":[{"extracted_events":[{"introduced":"a8b793db3d6ffe91d62f81baf41b1dab4cd78fb6"},{"last_affected":"a8b793db3d6ffe91d62f81baf41b1dab4cd78fb6"}],"source":"AFFECTED_FIELD"}],"cwe_ids":["CWE-113"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43966.json"},"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/gun/commit/4f35609eb37109b106a863fc9ba83d7ee64e3e42"},{"type":"PACKAGE","url":"https://github.com/ninenines/cowlib"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/ninenines/cowboy","events":[{"introduced":"04ca4c5d31a92d4d3de087bbd7d6021dc4a6d409"},{"fixed":"f77cb9b5e730e300fffb551db1ba5d1c4ed878ef"}],"database_specific":{"extracted_events":[{"introduced":"2.9.0"},{"last_affected":"2.9.0"}],"source":["AFFECTED_FIELD","REFERENCES"]}},{"type":"GIT","repo":"https://github.com/ninenines/gun","events":[{"introduced":"0"},{"fixed":"4f35609eb37109b106a863fc9ba83d7ee64e3e42"}],"database_specific":{"source":"REFERENCES"}}],"versions":["2.9.0","2.15.0","2.14.2","2.14.1","2.14.0","2.13.0","2.12.0","2.11.0","2.10.0","2.3.0","2.2.0","2.1.0","2.0.1","2.0.0","2.0.0-rc.2","2.0.0-rc.1","2.0.0-pre.2","2.0.0-pre.1","1.3.0","1.2.0","1.1.0","1.0.0","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":"1.7.5","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"}]}