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National Vulnerability Database

National Vulnerability Database

NVD

National Vulnerability Database
  1. Vulnerabilities

CVE-2026-43966 Detail

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.


Metrics

 
NVD enrichment efforts reference publicly available information to associate vector strings. CVSS information contributed by other sources is also displayed.
CVSS 4.0 Severity and Vector Strings:

NIST CVSS score
NIST: NVD
N/A
NVD assessment not yet provided.

Nist CVSS score does not match with CNA score
CNA:  EEF
CVSS-B 6.3 MEDIUM
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

References to Advisories, Solutions, and Tools

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URL Source(s) Tag(s)
https://cna.erlef.org/cves/CVE-2026-43966.html EEF
https://github.com/ninenines/cowboy/commit/f77cb9b5e730e300fffb551db1ba5d1c4ed878ef EEF
https://github.com/ninenines/gun/commit/4f35609eb37109b106a863fc9ba83d7ee64e3e42 EEF
https://osv.dev/vulnerability/EEF-CVE-2026-43966 EEF

Weakness Enumeration

CWE-ID CWE Name Source
CWE-113 Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') EEF  

Change History

1 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2026-43966
NVD Published Date:
06/08/2026
NVD Last Modified:
06/08/2026
Source:
EEF