CVE-2021-20270 : What You Need to Know

An infinite loop in SMLLexer in Pygments versions 1.5 to 2.7.3 may lead to denial of service when performing syntax highlighting of a Standard ML (SML) source file, as demonstrated by input that only contains the "exception" keyword.

Understanding CVE-2021-20270

This CVE affects the 'python-pygments' package, specifically version 2.7.4. It involves an infinite loop in SMLLexer.

What is CVE-2021-20270?

CVE-2021-20270 is a vulnerability in Pygments that allows an attacker to cause a denial of service by exploiting an infinite loop in SMLLexer.

The Impact of CVE-2021-20270

The impact of this CVE is the potential denial of service when syntax highlighting an SML source file, affecting the availability of the service.

Technical Details of CVE-2021-20270

This section provides detailed technical information about the vulnerability.

Vulnerability Description

The vulnerability arises from an infinite loop in SMLLexer in Pygments versions 1.5 to 2.7.3.

Affected Systems and Versions

Affected systems include those running Pygments versions 1.5 to 2.7.3, with version 2.7.4 being specifically affected.

Exploitation Mechanism

The vulnerability can be exploited by providing input containing only the "exception" keyword, triggering the infinite loop.

Mitigation and Prevention

To mitigate the risks associated with CVE-2021-20270, certain steps need to be taken.

Immediate Steps to Take

Update to a fixed version of Pygments that addresses the infinite loop issue.
Restrict access to systems running affected versions to trusted users only.

Long-Term Security Practices

Regularly update software packages and libraries to patched versions.
Implement robust input validation mechanisms to prevent malicious input.

Patching and Updates

Ensure timely application of security patches released by Pygments to address vulnerabilities like CVE-2021-20270.