CVE-2021-29416 Explained : Impact and Mitigation

This article discusses CVE-2021-29416, an issue discovered in PortSwigger Burp Suite before 2021.2 that could lead to the leakage of NetNTLM hashes on Windows systems. Learn about the impact, technical details, and mitigation strategies below.

Understanding CVE-2021-29416

CVE-2021-29416 is a vulnerability found in PortSwigger Burp Suite that allows malicious requests to bypass the upstream proxy configuration, potentially resulting in the exposure of NetNTLM hashes.

What is CVE-2021-29416?

CVE-2021-29416 is a security issue in PortSwigger Burp Suite prior to version 2021.2. Attackers can manipulate a malicious request to avoid respecting the configured proxy settings, leading to the unauthorized leakage of NetNTLM hashes on vulnerable Windows systems.

The Impact of CVE-2021-29416

Exploitation of this vulnerability could allow threat actors to obtain sensitive NetNTLM hashes from Windows machines that do not block outbound Server Message Block (SMB) traffic. This could potentially lead to unauthorized access and further compromise of affected systems.

Technical Details of CVE-2021-29416

The technical details of CVE-2021-29416 include:

Vulnerability Description

The vulnerability allows a malicious request in PortSwigger Burp Suite to bypass the configured proxy settings, leading to the exposure of NetNTLM hashes on Windows systems.

Affected Systems and Versions

PortSwigger Burp Suite versions prior to 2021.2 are affected by this vulnerability. Windows systems that do not block outbound SMB traffic may be particularly at risk.

Exploitation Mechanism

By manipulating a malicious request, attackers can trick the application into disregarding the upstream proxy configuration, enabling the leakage of NetNTLM hashes.

Mitigation and Prevention

To mitigate the risks associated with CVE-2021-29416, consider the following:

Immediate Steps to Take

Upgrade PortSwigger Burp Suite to version 2021.2 or newer to eliminate the vulnerability.
Implement firewall rules to restrict outbound SMB traffic, especially from sensitive Windows systems.

Long-Term Security Practices

Regularly update and patch software to address known security vulnerabilities.
Monitor network traffic for suspicious activities that may indicate an exploitation attempt.

Patching and Updates

Stay informed about security updates and patches released by PortSwigger to address CVE-2021-29416 and other potential vulnerabilities.