VULNERABILITY INTELLIGENCE

CVE-2026-43966

CVSS score5.3 MEDIUM
EPSS probability0.26%
CISA KEVNot currently listed
Published2026-06-08
Last modified2026-10-14
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

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. cow_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. This issue affects cowlib: from 2.9.0 onward.

Weakness classification

  • 6b3ad84c-e1a6-4bf7-a703-f496b71e49db: CWE-113

Primary references