CVE-2020-5238 : Security Advisory and Response

GitHub Flavored Markdown (cmark-gfm) before version 0.29.0.gfm.1 is affected by a denial of service vulnerability due to inefficient table parsing. An attacker could exploit this issue to cause a denial of service attack.

Understanding CVE-2020-5238

This CVE describes a vulnerability in the table extension of GitHub Flavored Markdown that could be exploited for a denial of service attack.

What is CVE-2020-5238?

The table extension in GitHub Flavored Markdown before version 0.29.0.gfm.1 takes O(n * n) time to parse certain inputs, allowing an attacker to craft a markdown table that causes a denial of service. This issue does not impact the upstream cmark project.

The Impact of CVE-2020-5238

The vulnerability has a CVSS base score of 6.5, with a medium severity rating. It has a low attack complexity and requires low privileges, but can result in high availability impact.

Technical Details of CVE-2020-5238

GitHub Flavored Markdown (cmark-gfm) before version 0.29.0.gfm.1 is susceptible to a denial of service vulnerability due to inefficient table parsing.

Vulnerability Description

The table extension in GitHub Flavored Markdown takes O(n * n) time to parse certain inputs, enabling an attacker to create a markdown table that causes a denial of service.

Affected Systems and Versions

Product: cmark-gfm
Vendor: GitHub
Versions affected: < 0.29.0.gfm.1

Exploitation Mechanism

An attacker can craft a markdown table that takes an unreasonably long time to process, leading to a denial of service attack.

Mitigation and Prevention

To address CVE-2020-5238, follow these mitigation steps:

Immediate Steps to Take

Update to version 0.29.0.gfm.1 or later to fix the vulnerability.
Monitor for any unusual processing times related to markdown tables.

Long-Term Security Practices

Regularly update software to the latest versions to patch known vulnerabilities.
Implement input validation mechanisms to prevent similar denial of service attacks.

Patching and Updates

Ensure timely patching of software to address security vulnerabilities like the one described in CVE-2020-5238.