Package 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.

Rack's multipart parser buffers unbounded per-part headers, enabling DoS (memory exhaustion)
`Rack::Multipart::Parser` can accumulate unbounded data when a multipart part’s header block never terminates with the required blank line (`CRLFCRLF`). The parser keeps appending incoming bytes to memory without a size cap, allowing a remote attacker to exhaust memory and cause a denial of service (DoS).

Rack: Multipart parser buffers large non‑file fields entirely in memory, enabling DoS (memory exhaustion)
`Rack::Multipart::Parser` stores non-file form fields (parts without a `filename`) entirely in memory as Ruby `String` objects. A single large text field in a multipart/form-data request (hundreds of megabytes or more) can consume equivalent process memory, potentially leading to out-of-memory (OOM) conditions and denial of service (DoS).

Rack has a Possible Information Disclosure Vulnerability
A possible information disclosure vulnerability existed in `Rack::Sendfile` when running behind a proxy that supports `x-sendfile` headers (such as Nginx). Specially crafted headers could cause `Rack::Sendfile` to miscommunicate with the proxy and trigger unintended internal requests, potentially bypassing proxy-level access restrictions.

Rack has an unsafe default in Rack::QueryParser allows params_limit bypass via semicolon-separated parameters
`Rack::QueryParser` in version `< 2.2.18` 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.