Appendix A. Migrating from Cowboy 2.17 to 2.18

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Cowboy 2.18 fixes a number of security vulnerabilities and improves the security checklist.

Cowboy 2.18 updates Cowlib to 2.19.0. Both applications must be updated as they both contain security fixes.

Cowboy 2.18 requires Erlang/OTP 24.0 or greater.

A.1. Features added

Defense-in-depth: Add the max_cookies option to cowboy_req functions that parse cookies. This new limit is applied in addition to existing length limits. It defaults to 100. Note that the option can’t be overriden when parsing the cookie header via parse_header.

Concurrent processing of pipelined HTTP/1.1 requests was removed. Pipelined requests are still supported. HTTP/2 should be used when concurrent processing of requests is necessary.
Defense-in-depth: request URIs with a fragment component are now rejected instead of the component stripped.
Defense-in-depth: CR, LF and NUL bytes are now rejected everywhere applicable. Note that query strings may still contain urlencoded CR, LF or NUL bytes.
Defense-in-depth: integers now have a hard limit of 17 digits when parsing headers or using the int constraint. A custom constraint can be written should the limit be a problem.
The max_headers HTTP/1.1 option now better tracks duplicate header field lines.
A crash could occur during HTTP/2 Upgrade, it has been resolved.
HTTP/2 will now reject requests that have both :authority and host headers with values that are different.
HTTP/2 will now reject empty CONTINUATION frames in most cases to prevent abuse.
Websocket frames could get over max_frame_size under certain conditions. This is now resolved.
Noisy crashes could occur when the PROXY protocol is enabled; they should all have been resolved now.
Functions cowboy_req:read_urlencoded_body/2 and cowboy_req:read_and_match_urlencoded_body/3 will now use the correct defaults for options in all cases.