Crass: Deeply nested CSS blocks and functions can trigger a SystemStackError or excessive memory usage

Impact

Crass recursively parses CSS simple blocks and functions without a depth guard. An attacker-controlled value containing many deeply nested blocks can recurse until Ruby raises SystemStackError: stack level too deep, or can cause excessive memory usage.

Patches

This is fixed in Crass 1.0.7, which adds a configurable depth limit with a conservative default.

Workarounds

Add SystemStackError handling around Crass calls in your application. Buy more RAM.