Useragent is a user agent parser for Node.js. All versions as of time of publication contain one or more regular expressions that are vulnerable to Regular Expression Denial of Service (ReDoS).
Useragent is used to parse useragent headers. It uses several regular expressions to accomplish this. An attacker could edit their own headers, creating an arbitrarily long useragent string, causing the event loop and server to block.
An attacker could edit their own headers, creating an arbitrarily long useragent string, causing the event loop and server to block.