CVE-2026-43969

Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in ninenines cowlib allows HTTP request splitting and cookie smuggling via unvalidated cookie name and value fields. cow_cookie:cookie/1 in cowlib builds a client-side Cookie: request header from a list of name-value pairs without validating either field. An attacker who controls the cookie names or values passed to this function can inject ;, ,, CR, LF, or TAB characters into the serialized header. This enables two classes of attack: cookie smuggling within a single header (e.g. injecting ; admin=1 to introduce a phantom cookie that the receiving server treats as authentic) and HTTP request header splitting (injecting CRLF to append arbitrary headers or smuggle a complete second request against a shared upstream proxy). The decoder side (parse_cookie_name/1, parse_cookie_value/1) and setcookie/3 already validate and reject these characters; the encoder alone is missing the check. This issue affects cowlib: from 2.9.0 onward.

• CWE-93

• https://cna.erlef.org/cves/CVE-2026-43969.htmlVendor Advisory
• https://github.com/erlef/cowlib/commit/177953dd51540da11090666c1f007214127a1144Patch
• https://osv.dev/vulnerability/EEF-CVE-2026-43969Third Party Advisory

Published

May 11, 2026

Last Modified

Aug 18, 2026

Status

Modified

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