Rack QueryParser has an unsafe default allowing params_limit bypass via semicolon-separated parameters

Vulnerability Description

Rack is a modular Ruby web server interface. Prior to version 2.2.18, Rack::QueryParser enforces its params_limit only for parameters separated by &, while still splitting on both & and ;. As a result, attackers could use ; separators to bypass the parameter count limit and submit more parameters than intended. Applications or middleware that directly invoke Rack::QueryParser with its default configuration (no explicit delimiter) could be exposed to increased CPU and memory consumption. This can be abused as a limited denial-of-service vector. This issue has been patched in version 2.2.18.

References

• https://github.com/rack/rack/security/advisories/GHSA-625h-95r8-8xpm
• https://github.com/rack/rack/commit/54e4ffdd5affebcb0c015cc6ae74635c0831ed71