CVE-2021-28957 : Vulnerability Insights and Analysis

This article provides insights into CVE-2021-28957, an XSS vulnerability found in python-lxml's clean module before version 4.6.3. Learn about the impact, technical details, and mitigation steps.

Understanding CVE-2021-28957

CVE-2021-28957 is an XSS vulnerability discovered in python-lxml's clean module versions prior to 4.6.3. This flaw could allow remote attackers to execute arbitrary JavaScript code on users interacting with incorrectly sanitized HTML.

What is CVE-2021-28957?

CVE-2021-28957 is an XSS vulnerability in python-lxml versions before 4.6.3. By exploiting this flaw, malicious actors could inject and execute arbitrary JavaScript code in users' browsers when interacting with unclean HTML content.

The Impact of CVE-2021-28957

The impact of CVE-2021-28957 is significant as it enables attackers to bypass HTML sanitization mechanisms and run malicious JavaScript code in the context of unsuspecting users. This could result in various attacks, including stealing sensitive information or hijacking user sessions.

Technical Details of CVE-2021-28957

This section delves into the vulnerability description, affected systems and versions, as well as the exploitation mechanism.

Vulnerability Description

The XSS vulnerability in python-lxml versions before 4.6.3 arises from improper handling of the formaction attribute when disabling certain arguments in the Cleaner class. This oversight allows attackers to bypass the sanitizer and inject malicious JavaScript code.

Affected Systems and Versions

Python-lxml versions before 4.6.3 are affected by CVE-2021-28957. Users relying on these vulnerable versions are at risk of exploitation by remote attackers.

Exploitation Mechanism

By manipulating the safe_attrs_only and forms arguments in python-lxml's Cleaner class, attackers can evade HTML sanitization controls and inject JavaScript payloads via the formaction attribute. This exploitation method enables them to execute arbitrary code on unsuspecting users interacting with the tainted HTML.

Mitigation and Prevention

This section outlines immediate steps to take and long-term security practices to mitigate the risks posed by CVE-2021-28957.

Immediate Steps to Take

Update python-lxml to version 4.6.3 or later to patch the vulnerability.
Educate users on safe browsing practices to minimize the risk of executing malicious scripts.

Long-Term Security Practices

Regularly update software components to benefit from security patches and enhancements.
Implement content security policies (CSP) to restrict the execution of inline scripts and mitigate XSS attacks.

Patching and Updates

Stay informed about security advisories and CVE alerts related to python-lxml to deploy timely patches and updates that address identified vulnerabilities.