CVE-2021-42911 Explained : Impact and Mitigation

A Format String vulnerability exists in DrayTek Vigor 2960 <= 1.5.1.3, DrayTek Vigor 3900 <= 1.5.1.3, and DrayTek Vigor 300B <= 1.5.1.3 in the mainfunction.cgi file via a crafted HTTP message containing malformed QUERY STRING, which could let a remote malicious user execute arbitrary code.

Understanding CVE-2021-42911

What is CVE-2021-42911?

This CVE describes a Format String vulnerability in multiple DrayTek Vigor devices that could allow a remote attacker to execute arbitrary code.

The Impact of CVE-2021-42911

The vulnerability could lead to remote code execution by malicious users, potentially compromising the security and integrity of the affected systems.

Technical Details of CVE-2021-42911

Vulnerability Description

The vulnerability exists in the mainfunction.cgi file of specific DrayTek Vigor devices due to improper handling of crafted HTTP messages with malformed QUERY STRING.

Affected Systems and Versions

DrayTek Vigor 2960 <= 1.5.1.3
DrayTek Vigor 3900 <= 1.5.1.3
DrayTek Vigor 300B <= 1.5.1.3

Exploitation Mechanism

Attackers can exploit this vulnerability by sending specifically crafted HTTP messages containing malformed QUERY STRING, triggering the execution of arbitrary code.

Mitigation and Prevention

Immediate Steps to Take

Apply security patches provided by DrayTek as soon as they are available.
Monitor network traffic for any signs of exploitation attempts.

Long-Term Security Practices

Regularly update and patch all software and firmware to mitigate known vulnerabilities.
Implement network segmentation and access controls to limit the impact of potential attacks.
Conduct regular security assessments and penetration testing to identify and address security weaknesses.

Patching and Updates

It is crucial to keep all DrayTek Vigor devices up to date with the latest firmware and security patches to address this vulnerability.