CVE-2021-29991 Explained : Impact and Mitigation

This article provides detailed information about CVE-2021-29991, a vulnerability affecting Firefox and Thunderbird, allowing for a header splitting attack in HTTP/3 responses.

Understanding CVE-2021-29991

CVE-2021-29991 is a security vulnerability that impacts Mozilla Firefox and Thunderbird applications, enabling malicious actors to conduct a header splitting attack through HTTP/3 responses.

What is CVE-2021-29991?

The vulnerability arises from Firefox incorrectly accepting a newline in an HTTP/3 header, thus treating it as separate headers. This flaw can be exploited by attackers to carry out header splitting attacks on servers utilizing HTTP/3.

The Impact of CVE-2021-29991

Due to this vulnerability, systems running Firefox versions prior to 91.0.1 and Thunderbird versions before 91.0.1 are at risk of header splitting attacks, potentially leading to unauthorized data access and manipulation.

Technical Details of CVE-2021-29991

This section outlines the technical aspects of CVE-2021-29991, including the vulnerability description, affected systems, and exploitation mechanisms.

Vulnerability Description

The flaw in Firefox and Thunderbird allows threat actors to exploit HTTP/3 header processing, leading to header splitting attacks that could compromise server security and integrity.

Affected Systems and Versions

Mozilla Firefox versions less than 91.0.1 and Thunderbird versions preceding 91.0.1 are vulnerable to this security issue.

Exploitation Mechanism

By manipulating HTTP/3 headers, attackers can inject malicious content into server responses, potentially bypassing security measures and gaining unauthorized access.

Mitigation and Prevention

To safeguard systems from CVE-2021-29991, immediate action and long-term security practices are recommended to mitigate risks effectively.

Immediate Steps to Take

Users are advised to update Firefox and Thunderbird to versions 91.0.1 or later to patch the vulnerability and prevent potential header splitting attacks.

Long-Term Security Practices

Employing secure coding practices, monitoring network traffic for suspicious activities, and staying informed about security advisories can enhance overall system security.

Patching and Updates

Regularly installing software updates and security patches provided by Mozilla is crucial to address known vulnerabilities and protect against emerging threats.