CRLF injection in Proxy-Authorization header built from proxy_auth_fun in hackney

Overview

Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') vulnerability in hackney_http_connect in benoitc hackney allows HTTP Request Splitting via the value a proxy_auth_fun callback returns. After a 407 response from an HTTP CONNECT proxy, hackney_http_connect:handle_proxy_auth/11 calls the caller's proxy_auth_fun with the status code and the response headers and writes the returned binary into the Proxy-Authorization line of the CONNECT retry without checking it. A CR, LF or NUL byte in that value adds header lines to the request sent to the proxy.

The value is attacker-influenced when the callback derives it from untrusted data, for example from the proxy's challenge headers. Other caller-supplied values on the CONNECT path, such as the target host and the request headers, were already checked for control bytes.

This issue affects hackney: from 2.0.0 before 4.9.0.

Affected

• hackney >= 2.0.0 < 4.9.0
• benoitc/hackney >= 5df5a74a2817d5b12880d217db33253ff1fae1b5 < 5ee7d7d19eba27e774667d472feb1e93a08af7f9

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Workarounds

Check the value your proxy_auth_fun is about to return for CR, LF and NUL bytes and return {error, Reason} instead when one is present. The callback runs in the application, so the check can be made there.