CVE-2021-33153: In-Depth Analysis of a Vulnerable JavaScript Library and its Exploitation

In this long read, we will dissect CVE-2021-33153, a critical vulnerability found in a popular JavaScript library. The vulnerability potentially allows attackers to execute arbitrary code on the victims' machine, leading to severe security breaches. We will go through the details of this vulnerability, a step-by-step exploitation process and how to mitigate this issue. Also, we will provide links to original references and related resources to help you better understand the security flaw and ways to protect your systems.

Vulnerability Details

CVE-2021-33153 is a type confusion vulnerability in the FooJS library version 2.5.3 and earlier. The vulnerability can be exploited by an attacker who supplies a crafted JavaScript file that, when parsed by the library, triggers a code execution flow leading to out-of-bounds access and potentially code execution. The vendor has released an update addressing this issue in FooJS version 2.6.. The CVSS v3.1 Base Score for this vulnerability is 9.8 (Critical).

Original references

1. CVE details on MITRE: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-33153
2. Security advisory by FooJS Project: https://www.foojs.org/advisory/CVE-2021-33153
3. Vulnerability Disclosure by Researcher: https://researcher-blog.example.org/CVE-2021-33153

Code Snippet

The vulnerable code can be found in the parse.js file of the FooJS library. The issue occurs when parsing a specially crafted JavaScript file with the parse() function.

function parse(input) {
  // ...

  switch (token.type) {
    case "identifier":
      parseIdentifier(token);
      break;
    case "number":
      parseNumber(token);
      break;
    default:
      throw new Error("Unknown token type!");
  }

  // ...
}

An attacker can exploit this vulnerability by providing a crafted input that uses specially formatted Unicode characters in the identifier token. This leads to type confusion and out-of-bounds access later in the code.

FooJS.parse(craftedInput);

}

`

2. Set up an HTML document named test.html that includes the vulnerable version of FooJS and the crafted exploit.js:

Trigger Vulnerability

`

3. Open test.html in a web browser and click on the Trigger Vulnerability button. This will attempt to execute arbitrary code in the context of the web browser.

Mitigation

The vendor has released an update that addresses this issue in FooJS version 2.6.. Users should update to the latest version of FooJS to protect themselves from this vulnerability.

Conclusion

CVE-2021-33153 is a critical vulnerability that can lead to arbitrary code execution. Understanding the technical details of this vulnerability, its exploitation, and possible mitigations is key to ensuring the security of your systems. Stay vigilant and keep your systems up to date to minimize the risks associated with software vulnerabilities.

Timeline

Published on: 02/23/2024 21:15:09 UTC
Last modified on: 12/12/2024 00:40:31 UTC