This post will discuss a recently discovered vulnerability in Firefox browsers, specifically versions below 119. Identified as CVE-2023-5723, this vulnerability points to an issue where an attacker might temporarily gain access to a website's script and create a cookie with invalid characters using document.cookie. This could trigger unexpected behavior within the website, which could have potential security implications. In this post, we'll go through the vulnerability in detail, discussing the exploit steps, possible impacts, and mitigation steps.

Before we dig deeper into this vulnerability, it is essential to understand that Firefox < 119 is affected. Therefore, it is necessary to keep your browser up-to-date to avoid such risks.

Exploit Details

This Firefox vulnerability arises from an insecure use of document.cookie and allows an attacker to set a cookie with invalid characters. Cookies are a crucial aspect of web applications, as they help manage user sessions and retain authentication. Typically, cookies would be expected to be alphanumeric and might have specific special characters.

However, this vulnerability results from allowing cookies with any unintentional invalid characters, possibly causing website errors and other unpredictable behavior. An attacker could exploit this vulnerability by executing scripts on a vulnerable site that create and set a cookie with invalid characters:

// Exploit code snippet
document.cookie = "insecure_cookie=test%00value";

The above code snippet sets a cookie named insecure_cookie and contains an invalid null byte %00 in the cookie value. Due to the vulnerability in the affected Firefox browsers, this value would be allowed and might cause unexpected behavior within the website. This vulnerability is identified and documented in the following original sources:

1. CVE-2023-5723 - Official CVE description and details
2. Mozilla Firefox Security Advisories - Mozilla's announcement and security advisories

Impacts and Risks

The exploitation of this vulnerability might lead to several risks to websites, their users, and the affected browsers:

1. Website errors and unexpected behavior: Allowing invalid characters in cookies might trigger script errors or create exceptions within the web application's code that might lead to malfunction, broken functionality, or even complete denial-of-service (DoS) situations. Furthermore, incorrectly handling cookies could have detrimental side effects for all users.

2. Cross-site scripting (XSS): In certain cases, attackers might exploit this vulnerability to execute malicious scripts within the vulnerable website's context, leading to a possible cross-site scripting (XSS) attack. This could allow the attackers unauthorized access to user data and potentially aid them in conducting further exploits.

3. User privacy and data breaches: Setting a cookie with invalid characters could enable the attacker to hijack user sessions by manipulating the setting, deleting, or forging cookies. This can lead to unauthorized access to user accounts, identity theft, and further data breaches.

To ensure that you are protected against this vulnerability, follow these steps

1. Update your Firefox browser: Always keep your Firefox browser updated to the latest version. The issue only affects Firefox before version 119. By updating to a later version, you remain protected.

2. Secure document.cookie usage: Web application developers can secure their document.cookie usage by only allowing valid characters for the cookie names and values and validating cookies before setting them. Consider implementing a proper sanitization library to clean input data before generating cookies.

3. CSP and X-Content-Type-Options: Implement Content Security Policy (CSP) and set the 'X-Content-Type-Options' header properly. These headers protect against cross-site scripting (XSS) attacks and malicious code execution.

In conclusion, the CVE-2023-5723 vulnerability affects Firefox browsers and can be exploited by setting cookies with invalid characters via document.cookie. The issue might lead to a significant security risk of website errors, data breaches, and unauthorized access to user accounts. It is essential to keep your browser updated to mitigate such risks and ensure the proper handling of cookies within your web applications.

Timeline

Published on: 10/25/2023 18:17:44 UTC
Last modified on: 11/01/2023 19:14:35 UTC