CVE-2021-39221 Explained : Impact and Mitigation

Nextcloud Contacts application prior to version 4.0.3 is susceptible to a stored Cross-Site Scripting (XSS) vulnerability.

Understanding CVE-2021-39221

Nextcloud Contacts application has a critical stored XSS vulnerability that requires user interaction for exploitation.

What is CVE-2021-39221?

The vulnerability in Nextcloud Contacts allows attackers to execute arbitrary script code in a user's browser when a malicious file is right-clicked and opened in a new tab.

The Impact of CVE-2021-39221

The vulnerability has a CVSS base score of 6.4 (Medium severity) with high impacts on confidentiality and integrity but no availability impact. User interaction is required for exploitation.

Technical Details of CVE-2021-39221

Nextcloud Contacts XSS vulnerability detailed information.

Vulnerability Description

The issue stems from improper handling of user-supplied data, leading to unvalidated script execution.

Affected Systems and Versions

Vendor: Nextcloud
Product: security-advisories
Versions Affected: < 4.0.3

Exploitation Mechanism

Attack Vector: Network
Attack Complexity: High
Privileges Required: Low
User Interaction: Required

Mitigation and Prevention

Best practices to mitigate and prevent the CVE-2021-39221 vulnerability.

Immediate Steps to Take

Upgrade Nextcloud Contacts to version 4.0.3 or later.
Use modern browsers with support for Content-Security-Policy.

Long-Term Security Practices

Implement Content-Security-Policy in applications and browsers.
Train users on safe browsing practices to avoid similar XSS attacks.

Patching and Updates

Regularly check for security advisories and apply patches promptly to prevent exploitation.