CVE-2026-43971

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Source
https://cve.org/CVERecord?id=CVE-2026-43971
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-43971.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-43971
Aliases
Downstream
Published
2026-08-18T09:01:53Z
Modified
2026-08-22T03:31:16Z
Severity
  • 6.3 (Medium) CVSS_V4 - CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N CVSS Calculator
Summary
Link Header Directive Smuggling via Unescaped target/rel/Attribute Keys in cow_link:link/1
Details

Improper Encoding or Escaping of Output vulnerability in ninenines cowlib allows Link header directive smuggling via unescaped special characters in cow_link:link/1.

cow_link:do_link/1 in cowlib interpolates the target URI, rel value, and attribute keys directly into the serialized Link: header value without escaping or token-grammar validation. A > byte in target prematurely closes the URI slot, allowing an attacker to append additional link entries with attacker-chosen rel directives. A " or \ in rel escapes the quoted string and opens new parameters. Any byte — including whitespace, =, and " — in an attribute key is emitted verbatim. Because browsers act on Link: directives such as rel="preconnect", rel="preload", and rel="prerender", an attacker who can influence these fields in an application that round-trips parsed Link headers through cow_link:link/1 can force victim browsers to make out-of-band connections to attacker-controlled origins.

This issue affects cowlib: from 2.9.0 onward.

Database specific 
{
    "cna_assigner": "EEF",
    "cwe_ids": [
        "CWE-116"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43971.json",
    "unresolved_ranges": [
        {
            "extracted_events": [
                {
                    "introduced": "2.9.0"
                },
                {
                    "fixed": "*"
                },
                {
                    "introduced": "485d58dfa91b91d98135dc95e5615f421715dae5"
                },
                {
                    "fixed": "89da27ee4c241f5d649ba7d9b7f2188918af6cea"
                }
            ],
            "source": "AFFECTED_FIELD"
        }
    ]
}
References

Affected packages

Git / github.com/ninenines/cowlib

Affected ranges

Type
GIT
Repo
https://github.com/ninenines/cowlib
Events
Introduced
0 Unknown introduced commit / All previous commits are affected
Fixed
89da27ee4c241f5d649ba7d9b7f2188918af6cea
Database specific
Show details 
{
    "source": "REFERENCES"
}

Affected versions

0.*
0.1.0
0.2.0
0.3.0
0.4.0
0.5.0
0.5.1
0.6.0
0.6.1
0.6.2
1.*
1.0.0
1.0.1
1.1.0
1.2.0
1.3.0
2.*
2.0.0
2.0.0-pre.1
2.0.0-rc.1
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
2.15.0
2.16.0
2.16.1
2.17.0
2.17.1
2.18.0
2.19.0
2.2.0
2.2.1
2.3.0
2.4.0
2.5.0
2.5.1
2.6.0
2.7.0
2.7.1
2.7.2
2.7.3
2.8.0
2.9.0
2.9.1

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-43971.json"