{"apiVersion":"1.0","identifier":"CVE-2026-43971","description":"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.","publishedAt":"2026-08-18T09:17:14","lastModifiedAt":"2026-08-20T13:02:12","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-43971","cvssScore":6.3,"cvssVector":"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","epssProbability":0.00372,"riskScore":0.65,"affectedProduct":"cowlib","affectedVersions":">=2.9.0","vulnerabilityType":"Library","operatingSystems":[],"links":{"self":"https://www.redsauce.net/api/cves/CVE-2026-43971","webPages":{"es":"https://www.redsauce.net/es/cves/CVE-2026-43971","en":"https://www.redsauce.net/en/cves/CVE-2026-43971","fr":"https://www.redsauce.net/fr/cves/CVE-2026-43971","pt":"https://www.redsauce.net/pt/cves/CVE-2026-43971","de":"https://www.redsauce.net/de/cves/CVE-2026-43971","sk":"https://www.redsauce.net/sk/cves/CVE-2026-43971","el":"https://www.redsauce.net/el/cves/CVE-2026-43971"},"source":"https://nvd.nist.gov/vuln/detail/CVE-2026-43971"}}