CVE-2026-43971
Severity CVSS v4.0:
MEDIUM
Type:
Unavailable / Other
Publication date:
18/08/2026
Last modified:
18/08/2026
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.<br />
<br />
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.<br />
<br />
This issue affects cowlib: from 2.9.0 onward.
Impact
Base Score 4.0
6.30
Severity 4.0
MEDIUM