CVE-2021-26236 Explained : Impact and Mitigation

FastStone Image Viewer version 7.5 and below is impacted by a Stack-based Buffer Overflow vulnerability that affects the parsing functionality of CUR files. This vulnerability could be exploited by attackers to execute malicious code when a user interacts with a specially crafted CUR file.

Understanding CVE-2021-26236

This section delves into the specifics of CVE-2021-26236, outlining the vulnerability and its potential impact.

What is CVE-2021-26236?

FastStone Image Viewer v.<= 7.5 is susceptible to a Stack-based Buffer Overflow at 0x005BDF49, primarily impacting the CUR file parsing function related to the 'BitCount' file format field within the BITMAPINFOHEADER Structure. This compromise can lead to corruption of the Structure Exception Handler (SEH) and provides a pathway for threat actors to execute arbitrary code.

The Impact of CVE-2021-26236

The exploitation of CVE-2021-26236 could result in unauthorized remote code execution on systems running the vulnerable FastStone Image Viewer version 7.5 or below. Attackers could leverage this flaw by convincing a user to open or view a specially crafted CUR file, thereby compromising the target system.

Technical Details of CVE-2021-26236

In this section, we explore the technical aspects related to CVE-2021-26236, including the vulnerability description, affected systems, and the exploitation mechanism.

Vulnerability Description

The vulnerability stems from a Stack-based Buffer Overflow in FastStone Image Viewer v.<= 7.5, triggered during the parsing of CUR files. Specifically, the issue lies within the 'BitCount' file format field of the BITMAPINFOHEADER Structure, leading to SEH corruption.

Affected Systems and Versions

FastStone Image Viewer versions 7.5 and below are confirmed to be impacted by this vulnerability. Users running these versions are advised to take immediate action to mitigate the risk of exploitation.

Exploitation Mechanism

To exploit CVE-2021-26236, attackers need to craft a specially malformed CUR file and entice a user to open or view the file using the vulnerable FastStone Image Viewer software. Upon interaction with the malicious file, the attacker can achieve code execution on the target system.

Mitigation and Prevention

In this segment, we discuss the steps that users and administrators can take to mitigate the risks posed by CVE-2021-26236 and prevent potential exploitation.

Immediate Steps to Take

Immediately update FastStone Image Viewer to a non-vulnerable version beyond 7.5 to safeguard systems from potential attacks leveraging CVE-2021-26236. Exercise caution when handling CUR files from untrusted sources.

Long-Term Security Practices

Incorporate secure coding practices, regular software updates, and user awareness training within your organization to bolster overall cybersecurity hygiene and prevent similar vulnerabilities from being exploited.

Patching and Updates

Stay informed about security advisories and patches released by FastStone Image Viewer. Promptly apply security updates to ensure that known vulnerabilities like CVE-2021-26236 are mitigated effectively.