Vulnerability Details 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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.0
EPSS Ranking 6.5%
CVSS Severity
CVSS v3 Score 3.2
References
Products affected by CVE-2026-43969
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cpe:2.3:a:ninenines:cowlib:2.10.0
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cpe:2.3:a:ninenines:cowlib:2.10.1
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cpe:2.3:a:ninenines:cowlib:2.11.0
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cpe:2.3:a:ninenines:cowlib:2.12.0
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cpe:2.3:a:ninenines:cowlib:2.12.1
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cpe:2.3:a:ninenines:cowlib:2.13.0
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cpe:2.3:a:ninenines:cowlib:2.14.0
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cpe:2.3:a:ninenines:cowlib:2.15.0
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cpe:2.3:a:ninenines:cowlib:2.16.0
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cpe:2.3:a:ninenines:cowlib:2.16.1
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cpe:2.3:a:ninenines:cowlib:2.9.0
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cpe:2.3:a:ninenines:cowlib:2.9.1