GHSA-Q2HR-2G5M-VWHR brace-expansion: Quadratic-time expansion of the `{a},b}` rewrite causes CPU denial of service

Summary Expanding a,b-shaped input takes time quadratic in the number of literal characters, blocking the event loop. Bash preserves a quirk where a brace group followed by a comma set still expands a,b. The parser implements this by rewriting the string and restarting the scan. Each pass absorbs...