new commonmark.Parser().parse("[" + "\\".repeat(n)) runs in exponential time:

[\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ → 1.2 seconds
[\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ → 1.8 seconds
[\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ → 2.9 seconds
[\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ → 4.7 seconds
[\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ → 7.5 seconds
[\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ → 12.5 seconds
[\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ → 20.2 seconds
[\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ → 32.8 seconds
[\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ → 52.7 seconds
[\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ → 83.9 seconds
[\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ → 137.8 seconds

This could be a denial of service vulnerability in an application that parses user input.