CVE-2026-47069

Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in benoitc hackney allows HTTP Response Splitting. The hackney_cookie:setcookie/3 function in src/hackney_cookie.erl validates the Name and Value arguments against CRLF and control characters, but concatenates the domain and path options verbatim into the output iolist with no equivalent check. An attacker who controls either option — for example by supplying a Host header value forwarded as the cookie domain, or a request path forwarded as the cookie path — can inject a literal CRLF sequence and arbitrary additional Set-Cookie headers into the HTTP response.

This issue affects hackney: from 0.9.0 before 4.0.1.

Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in benoitc hackney allows HTTP Response Splitting. The hackney_cookie:setcookie/3 function in src/hackney_cookie.erl validates the Name and Value arguments against CRLF and control characters, but concatenates the domain and path options verbatim into the output iolist with no equivalent check. An attacker who controls either option — for example by supplying a Host header value forwarded as the cookie domain, or a request path forwarded as the cookie path — can inject a literal CRLF sequence and arbitrary additional Set-Cookie headers into the HTTP response.

This issue affects hackney: from 0.9.0 before 4.0.1.

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

1. Call hackney_cookie:setcookie(<<"sid">>, <<"abc">>, [{path, <<"/x\r\nSet-Cookie: admin=1; Path=/">>}]).
2. The returned binary contains a literal \r\n followed by a second Set-Cookie: line.
3. 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

• Introduction commit: https://github.com/benoitc/hackney/commit/602d5c7f2ea4acbc83ed75230655d935a0750ebc
• Patch commit: https://github.com/benoitc/hackney/commit/8e02b99c28aea1b3fa2ddc0e66f51fe5bb0ac540

Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in benoitc hackney allows HTTP Response Splitting. The hackney_cookie:setcookie/3 function in src/hackney_cookie.erl validates the Name and Value arguments against CRLF and control characters, but concatenates the domain and path options verbatim into the output iolist with no equivalent check. An attacker who controls either option — for example by supplying a Host header value forwarded as the cookie domain, or a request path forwarded as the cookie path — can inject a literal CRLF sequence and arbitrary additional Set-Cookie headers into the HTTP response.

This issue affects hackney: from 0.9.0 before 4.0.1.

Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in benoitc hackney allows HTTP Response Splitting. The hackney_cookie:setcookie/3 function in src/hackney_cookie.erl validates the Name and Value arguments against CRLF and control characters, but concatenates the domain and path options verbatim into the output iolist with no equivalent check. An attacker who controls either option — for example by supplying a Host header value forwarded as the cookie domain, or a request path forwarded as the cookie path — can inject a literal CRLF sequence and arbitrary additional Set-Cookie headers into the HTTP response.

This issue affects hackney: from 0.9.0 before 4.0.1.

Summary

Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in benoitc hackney allows HTTP Response Splitting. The hackney_cookie:setcookie/3 function in src/hackney_cookie.erl validates the Name and Value arguments against CRLF and control characters, but concatenates the domain and path options verbatim into the output iolist with no equivalent check. An attacker who controls either option — for example by supplying a Host header value forwarded as the cookie domain, or a request path forwarded as the cookie path — can inject a literal CRLF sequence and arbitrary additional Set-Cookie headers into the HTTP response.

This issue affects hackney: from 0.9.0 before 4.0.1.

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

1. Call hackney_cookie:setcookie(<<"sid">>, <<"abc">>, [{path, <<"/x\r\nSet-Cookie: admin=1; Path=/">>}]).
2. The returned binary contains a literal \r\n followed by a second Set-Cookie: line.
3. 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

• Introduction commit: https://github.com/benoitc/hackney/commit/602d5c7f2ea4acbc83ed75230655d935a0750ebc
• Patch commit: https://github.com/benoitc/hackney/commit/8e02b99c28aea1b3fa2ddc0e66f51fe5bb0ac540