Uncontrolled Resource Consumption in brace-expansion

Summary

The brace-expansion library generates arbitrary strings containing a common prefix and suffix. In versions prior to 1.1.21, 2.x prior to 2.1.7, 3.x prior to 3.0.9, and 4.x through 5.x prior to 5.0.12, the expand function handles untrusted {a},b}-shaped patterns with many trailing closing braces by restarting its scan once for each trailing closing brace. The successive full-input rescans with linear working-string growth cause quadratic CPU time and memory pressure that can block the Node.js event loop. The process eventually recovers, making the impact a recoverable CPU denial of service. This issue is fixed in versions 1.1.21, 2.1.7, 3.0.9, and 5.0.12.