Summary
CRLF injection in hackney_cookie:setcookie/3 (src/hackney_cookie.erl). The function validates Name and Value against CR/LF and control characters but concatenates the domain and path options verbatim into the output binary. If either option carries attacker-controlled data, a Host header forwarded as the cookie domain, a request URI forwarded as the cookie path, a \r\n in the value splits the Set-Cookie header and lets the attacker inject additional headers into the HTTP response.
Details
1. Asymmetric validation
Lines 27–34 of hackney_cookie.erl run binary:match on Name and Value, rejecting =, ,, ;, whitespace, \r, \n, \013, and \014. The Domain and Path options (lines 47 and 51) skip this check entirely and land straight in the result iolist:
[<<"; Domain=">>, Domain]
[<<"; Path=">>, Path]
iolist_to_binary(...) on line 63 flattens everything and returns it to the caller.
2. Injection
A Path of <<"/x\r\nSet-Cookie: admin=1; Path=/">> produces a binary with a literal \r\n. Written into a Set-Cookie response header, the receiving HTTP parser splits it into two headers — one legitimate, one attacker-controlled.
3. Realistic trigger
Common patterns: keying the cookie domain off Host, deriving the path from the request URI, or copying a Location path into a cookie. Any of these lets a remote attacker control the injected content.
PoC
- Call
hackney_cookie:setcookie(<<"sid">>, <<"abc">>, [{path, <<"/x\r\nSet-Cookie: admin=1; Path=/">>}]).
- The returned binary contains a literal
\r\n followed by a second Set-Cookie: line.
- Write the result into a
Set-Cookie response header — the client parses two headers, including admin=1.
Impact
Cookie injection / HTTP response splitting at the hackney_cookie API boundary. Affects hackney 0.9.0 through 4.0.0 wherever domain or path options are populated from request data. Exploitation can overwrite session/auth cookies, fix cookies, or strip Secure/HttpOnly flags. CVSS v4.0: 2.1 (LOW) — requires attacker-controlled input to reach the domain or path option.
Resources
References
Summary
CRLF injection in
hackney_cookie:setcookie/3(src/hackney_cookie.erl). The function validatesNameandValueagainst CR/LF and control characters but concatenates thedomainandpathoptions verbatim into the output binary. If either option carries attacker-controlled data, aHostheader forwarded as the cookie domain, a request URI forwarded as the cookie path, a\r\nin the value splits theSet-Cookieheader and lets the attacker inject additional headers into the HTTP response.Details
1. Asymmetric validation
Lines 27–34 of
hackney_cookie.erlrunbinary:matchonNameandValue, rejecting=,,,;, whitespace,\r,\n,\013, and\014. TheDomainandPathoptions (lines 47 and 51) skip this check entirely and land straight in the result iolist:iolist_to_binary(...)on line 63 flattens everything and returns it to the caller.2. Injection
A
Pathof<<"/x\r\nSet-Cookie: admin=1; Path=/">>produces a binary with a literal\r\n. Written into aSet-Cookieresponse header, the receiving HTTP parser splits it into two headers — one legitimate, one attacker-controlled.3. Realistic trigger
Common patterns: keying the cookie domain off
Host, deriving the path from the request URI, or copying aLocationpath into a cookie. Any of these lets a remote attacker control the injected content.PoC
hackney_cookie:setcookie(<<"sid">>, <<"abc">>, [{path, <<"/x\r\nSet-Cookie: admin=1; Path=/">>}]).\r\nfollowed by a secondSet-Cookie:line.Set-Cookieresponse header — the client parses two headers, includingadmin=1.Impact
Cookie injection / HTTP response splitting at the
hackney_cookieAPI boundary. Affects hackney 0.9.0 through 4.0.0 whereverdomainorpathoptions are populated from request data. Exploitation can overwrite session/auth cookies, fix cookies, or stripSecure/HttpOnlyflags. CVSS v4.0: 2.1 (LOW) — requires attacker-controlled input to reach thedomainorpathoption.Resources
References