Vulnerability Instance

Rack has an Unbounded-Parameter DoS in Rack::QueryParser
## Summary

`Rack::QueryParser` parses query strings and
`application/x-www-form-urlencoded` bodies into Ruby data structures
without imposing any limit on the number of parameters, allowing
attackers to send requests with extremely large numbers of parameters.

## Details

The vulnerability arises because `Rack::QueryParser` iterates over
each `&`-separated key-value pair and adds it to a Hash without
enforcing an upper bound on the total number of parameters. This
allows an attacker to send a single request containing hundreds of
thousands (or more) of parameters, which consumes excessive memory
and CPU during parsing.

## Impact

An attacker can trigger denial of service by sending specifically
crafted HTTP requests, which can cause memory exhaustion or pin CPU
resources, stalling or crashing the Rack server. This results in
full service disruption until the affected worker is restarted.

## Mitigation

- Update to a version of Rack that limits the number of parameters parsed, or
- Use middleware to enforce a maximum query string size or parameter count, or
- Employ a reverse proxy (such as Nginx) to limit request sizes and
  reject oversized query strings or bodies.

Limiting request body sizes and query string lengths at the web
server or CDN level is an effective mitigation.