CVE-2021-41816 Explained : Impact and Mitigation

CVE-2021-41816, also known as CGI.escape_html vulnerability in Ruby, involves an integer overflow and buffer overflow in certain Ruby versions, affecting CGI gem before 0.3.1.

Understanding CVE-2021-41816

This vulnerability impacts the security of Ruby versions before 2.7.5 and 3.x before 3.0.3 on platforms with different byte sizes for size_t and long variables.

What is CVE-2021-41816?

CVE-2021-41816, a vulnerability in CGI.escape_html in Ruby, allows an attacker to trigger an integer overflow and a subsequent buffer overflow via a lengthy string, particularly on platforms like Windows.

The Impact of CVE-2021-41816

This vulnerability could be exploited by an attacker to execute arbitrary code by carefully crafting a malicious string, potentially leading to a denial of service or remote code execution.

Technical Details of CVE-2021-41816

This section provides insights into the specifics of the CGI.escape_html vulnerability in Ruby.

Vulnerability Description

The vulnerability arises due to an integer overflow and resultant buffer overflow triggered by a lengthy input string.

Affected Systems and Versions

Ruby versions prior to 2.7.5 and 3.x before 3.0.3 are vulnerable.
CGI gem versions earlier than 0.3.1 for Ruby are also affected.

Exploitation Mechanism

An attacker can exploit this vulnerability by providing a long string as input, causing an integer overflow and subsequently leading to a buffer overflow.

Mitigation and Prevention

It's crucial to take immediate steps to mitigate the risks associated with CVE-2021-41816.

Immediate Steps to Take

Update Ruby to version 2.7.5 or 3.0.3 to patch the vulnerability.
Ensure the CGI gem is updated to version 0.3.1 or later.

Long-Term Security Practices

Practice secure coding to avoid integer overflow vulnerabilities.
Regularly monitor security advisories and promptly apply patches.

Patching and Updates

Apply patches provided by Ruby for the affected versions to prevent exploitation of this vulnerability.