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.

Tornado vulnerable to excessive logging caused by malformed multipart form data
### Summary

When Tornado's ``multipart/form-data`` parser encounters certain errors, it logs a warning but continues trying to parse the remainder of the data. This allows remote attackers to generate an extremely high volume of logs, constituting a DoS attack. This DoS is compounded by the fact that the logging subsystem is synchronous.

### Affected versions

All versions of Tornado prior to 6.5 are affected. The vulnerable parser is enabled by default.

### Solution

Upgrade to Tornado version 6.5. In the meantime, risk can be mitigated by blocking `Content-Type: multipart/form-data` in a proxy.