CVE-2021-27291 Explained : Impact and Mitigation

A vulnerability tracked as CVE-2021-27291 exists in pygments versions 1.1+ up to 2.7.4. The issue stems from the usage of regular expressions with exponential or cubic complexity, leading to a ReDoS (Regular Expression Denial of Service) vulnerability. An attacker could exploit this flaw to trigger a denial of service attack.

Understanding CVE-2021-20657

This section delves deeper into the details and impact of CVE-2021-20657.

What is CVE-2021-20657?

The vulnerability exists in pygments versions 1.1+ to 2.7.4 due to certain regular expressions with high complexity, paving the way for a denial of service attack through malicious input by an attacker.

The Impact of CVE-2021-20657

By crafting specifically designed input, malicious actors can exploit this vulnerability to launch denial of service attacks on systems utilizing affected pygments versions.

Technical Details of CVE-2021-20657

Let's explore the technical aspects of the vulnerability.

Vulnerability Description

The vulnerability arises from the usage of regular expressions in pygments versions 1.1+ to 2.7.4, which have exponential or cubic worst-case complexity, leaving them vulnerable to ReDoS attacks.

Affected Systems and Versions

Pygments versions from 1.1 up to 2.7.4 are affected by this vulnerability, potentially exposing systems leveraging these versions to exploitation.

Exploitation Mechanism

Attackers can exploit this flaw by providing specially crafted input to the affected systems, triggering the vulnerability and leading to a denial of service scenario.

Mitigation and Prevention

Here are some essential steps to mitigate the risks associated with CVE-2021-20657.

Immediate Steps to Take

Update Pygments: Ensure that you update pygments to version 2.7.4 or higher to patch the vulnerability.
Input Validation: Implement robust input validation mechanisms to filter out potentially malicious input.

Long-Term Security Practices

Regular Security Audits: Conduct periodic security audits to identify and address vulnerabilities promptly.
Security Training: Provide security awareness training to developers and staff to enhance overall security posture.

Patching and Updates

Stay informed about security updates and patches released by pygments. Regularly apply patches and updates to ensure your systems are protected against known vulnerabilities.