CVE-2021-35955 : What You Need to Know

Contao >=4.0.0 allows backend XSS via HTML attributes to an HTML field. This vulnerability has been fixed in versions 4.4.56, 4.9.18, and 4.11.7.

Understanding CVE-2021-35955

This CVE relates to a cross-site scripting (XSS) vulnerability in Contao versions equal to or greater than 4.0.0.

What is CVE-2021-35955?

CVE-2021-35955 refers to a security issue in Contao where attackers can exploit backend XSS via HTML attributes in an HTML field.

The Impact of CVE-2021-35955

This vulnerability can enable malicious actors to execute scripts in a victim's browser, leading to potential data theft, unauthorized actions, or complete system compromise.

Technical Details of CVE-2021-35955

The technical details of CVE-2021-35955 are as follows:

Vulnerability Description

The vulnerability allows attackers to inject malicious scripts into the HTML field, posing a risk of XSS attacks.

Affected Systems and Versions

Contao versions equal to or greater than 4.0.0 are affected by this vulnerability.

Exploitation Mechanism

By inserting malicious HTML attributes into an HTML field, attackers can trigger XSS attacks in the Contao backend.

Mitigation and Prevention

To protect systems from CVE-2021-35955, follow these security measures:

Immediate Steps to Take

Update Contao to versions 4.4.56, 4.9.18, or 4.11.7 to apply the necessary patches.
Regularly monitor and sanitize user inputs to prevent injection of malicious scripts.

Long-Term Security Practices

Implement strict input validation and output encoding practices in web applications.
Educate developers and system administrators about secure coding practices to mitigate XSS risks.

Patching and Updates

Stay informed about security advisories from Contao and apply updates promptly to address any new vulnerabilities.