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TI-2026-32011 Aliases CVE-2026-43966GHSA-w4f7-4cxr-rv3c

HTTP Response Splitting via Non-VCHAR Bytes in cow_http_struct_hd:escape_string/2

Priority LOW 28CWE-113Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
Present
Impact type
—
Confidentiality · integrity · availability
None · None · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and GitHub.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00259 17th percentileScored 2026-11-07
Fix Fixed cowboy (Hex): 2.16.0gun (Hex): 2.16.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
nineninescowlib2.9.0 and later—No fix listedCNA
—cowboy (Hex)before 2.16.02.16.0Patch availableGHSA-w4f7-4cxr-rv3c
—gun (Hex)before 2.16.02.16.0Patch availableGHSA-w4f7-4cxr-rv3c
  • cowlib Vendorninenines Affected 2.9.0 and later Fixed in — No fix listed CNA
  • cowboy (Hex) Vendor— Affected before 2.16.0 Fixed in 2.16.0 Patch available GHSA-w4f7-4cxr-rv3c
  • gun (Hex) Vendor— Affected before 2.16.0 Fixed in 2.16.0 Patch available GHSA-w4f7-4cxr-rv3c

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*2.9.0 to before 2.16.0Vulnerableninenines
  • cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:* Versions 2.9.0 to before 2.16.0 Vulnerable ·ninenines

Remediation

  • Fix · GHSA-w4f7-4cxr-rv3c cowboy (Hex) Fixed in 2.16.0 Advisory →
  • Fix · GHSA-w4f7-4cxr-rv3c gun (Hex) Fixed in 2.16.0 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-43966
  2. 2026-10-03 Alias added: GHSA-w4f7-4cxr-rv3c
  3. 2026-10-14 Fix available: ninenines/cowlib@4401b858f2229abb3ea115c60924f6c77e5f8aa3 · CNA
  4. 2026-10-14 2 new references · CNA

References

Patch 3

Advisory 3

Other 4

  • TI-2026-06860 Unbounded chunk-size hex digits in cowlib cause quadratic CPU and memory DoS CVSS 4.0HIGH 8.7
  • TI-2026-32013 CR Injection in SSE Encoder Enables Event Splitting via cow_sse:event/1 CVSS 4.0MEDIUM 6.3
  • TI-2026-32014 Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1 CVSS 4.0LOW 2.1

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences