Denial of Service (DoS) Affecting fast-string-search Open this link in a new tab package, versions *

  • Exploit Maturity

    Proof of concept

  • Attack Complexity


  • Availability


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  • snyk-id


  • published

    15 Jun 2022

  • disclosed

    3 Feb 2022

  • credit

    Cristian-Alexandru Staicu

How to fix?

There is no fixed version for fast-string-search.


fast-string-search is a module that can search substrings in a string by using N-API and boyer-moore-magiclen.

Affected versions of this package are vulnerable to Denial of Service (DoS) when computations are incorrect for non-string inputs. One can cause the V8 to attempt reading from non-permitted locations and cause a segmentation fault due to the violation.


const fss = require('fast-string-search');

let res1 = fss.indexOfSkip("no way this will", "w");
let res2 = fss.indexOfSkip(1, 1); 


// you can also crash it after a very long useless computation, by running this instead of lines 6-11: 
let a = new Array(10000)
let res2 = fss.indexOfSkip(1, 1); // segfaults after 5 seconds


Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.

Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.

One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.

When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.

Two common types of DoS vulnerabilities:

  • High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.

  • Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm ws package