CVE-2026-43969

Description

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.

PUBLISHED Reserved 2026-05-04 | Published 2026-05-11 | Updated 2026-05-11 | Assigner EEF

Problem types

CWE-93 Improper Neutralization of CRLF Sequences ('CRLF Injection')

Product status

Credits

Peter Ullrich finder

References

cna.erlef.org/cves/CVE-2026-43969.html related third-party-advisory

osv.dev/vulnerability/EEF-CVE-2026-43969 related

github.com/...ommit/177953dd51540da11090666c1f007214127a1144 patch

cve.org (CVE-2026-43969)

nvd.nist.gov (CVE-2026-43969)

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