Regular Expression DoS and Node.js
Imagine you are trying to buy a ticket to your favorite JavaScript conference, and instead of getting the ticket page, you instead get 500 Internal Server Error. For some reason the site is down. You can’t do the thing that you want to do most and the conference is losing out on your purchase, all because the application is unavailable.
Availability is not often treated as a security problem, which it is, and it’s impacts are immediate, and deeply felt.
The attack surface for Node.js in regards to loss of availability is quite large, as we are dealing with a single event loop. If an attacker can control and block that event loop, then nothing else gets done.
There are many ways to block the event loop, one way an attacker can do that is with Regular Expression Denial of Service (ReDoS).
The Regular expression Denial of Service (ReDoS) is a Denial of Service attack, that exploits the fact that most Regular Expression implementations may reach extreme situations that cause them to work very slowly (exponentially related to input size). An attacker can then cause a program using a Regular Expression to enter these extreme situations and then hang for a very long time.
