CVE-2026-43966

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Source
https://cve.org/CVERecord?id=CVE-2026-43966
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-43966.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-43966
Aliases
Downstream
Published
2026-06-08T16:34:33Z
Modified
2026-10-21T02:57:55Z
Severity
  • 6.3 (Medium) CVSS_V4 - 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 CVSS Calculator
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.

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.

Database specific 
{
    "cna_assigner":  "EEF",
    "cwe_ids":  [
        "CWE-113"
    ],
    "osv_generated_from":  "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43966.json",
    "unresolved_ranges":  [
        {
            "extracted_events":  [
                {
                    "range":  [
                        {
                            "introduced":  "2.9.0"
                        },
                        {
                            "fixed":  "*"
                        }
                    ],
                    "source":  "AFFECTED_FIELD",
                    "strategy":  "StandardRange"
                }
            ]
        }
    ]
}
References

Affected packages

Git / github.com/ninenines/cowboy

Affected ranges

Type
GIT
Repo
https://github.com/ninenines/cowboy
Events
Introduced
0 Unknown introduced commit / All previous commits are affected
Fixed
f77cb9b5e730e300fffb551db1ba5d1c4ed878ef
Database specific
Show details 
{
    "extracted_events":  [
        {
            "range":  [
                {
                    "fixed":  "f77cb9b5e730e300fffb551db1ba5d1c4ed878ef"
                }
            ],
            "source":  "REFERENCES_COMMIT"
        }
    ]
}
Type
GIT
Repo
https://github.com/ninenines/cowlib
Events
Introduced
b34155f725245848dca3a505398e262b1d50f25b
Fixed
aca0ad953417b29bab2c41eeb4c37c98606c848b
Fixed
4401b858f2229abb3ea115c60924f6c77e5f8aa3
Fixed
a8b793db3d6ffe91d62f81baf41b1dab4cd78fb6
Database specific
Show details 
{
    "extracted_events":  [
        {
            "cpe":  "cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*",
            "range":  [
                {
                    "introduced":  "2.9.0"
                },
                {
                    "fixed":  "2.16.0"
                }
            ],
            "source":  "CPE_RANGE"
        },
        {
            "range":  [
                {
                    "fixed":  "4401b858f2229abb3ea115c60924f6c77e5f8aa3"
                }
            ],
            "source":  "REFERENCES_COMMIT"
        },
        {
            "range":  [
                {
                    "fixed":  "a8b793db3d6ffe91d62f81baf41b1dab4cd78fb6"
                }
            ],
            "source":  "REFERENCES_COMMIT"
        }
    ]
}
Type
GIT
Repo
https://github.com/ninenines/gun
Events
Introduced
0 Unknown introduced commit / All previous commits are affected
Fixed
4f35609eb37109b106a863fc9ba83d7ee64e3e42
Database specific
Show details 
{
    "extracted_events":  [
        {
            "range":  [
                {
                    "fixed":  "4f35609eb37109b106a863fc9ba83d7ee64e3e42"
                }
            ],
            "source":  "REFERENCES_COMMIT"
        }
    ]
}

Affected versions

0.*
0.10.0
0.2.0
0.4.0
0.6.0
0.6.1
0.8.0
0.8.1
0.8.2
0.8.3
0.8.4
0.8.5
0.8.6
0.9.0
1.*
1.0.0
1.0.0-pre.1
1.0.0-pre.2
1.0.0-pre.3
1.0.0-pre.4
1.0.0-pre.5
1.0.0-rc.1
1.1.0
1.2.0
1.3.0
2.*
2.0.0
2.0.0-pre.1
2.0.0-pre.10
2.0.0-pre.2
2.0.0-pre.3
2.0.0-pre.4
2.0.0-pre.5
2.0.0-pre.6
2.0.0-pre.7
2.0.0-pre.8
2.0.0-pre.9
2.0.0-rc.1
2.0.0-rc.2
2.0.0-rc.3
2.0.0-rc.4
2.0.1
2.1.0
2.10.0
2.10.1
2.11.0
2.12.0
2.12.1
2.13.0
2.14.0
2.14.1
2.14.2
2.15.0
2.2.0
2.2.1
2.2.2
2.3.0
2.4.0
2.5.0
2.6.0
2.6.1
2.6.2
2.6.3
2.7.0
2.8.0
2.9.0
2.9.1

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-43966.json"