CVE-2021-26929 : Exploit Details and Defense Strategies

An XSS issue was discovered in Horde Groupware Webmail Edition through 5.2.22, allowing attackers to send malicious JavaScript in plain text email messages.

Understanding CVE-2021-26929

This CVE relates to a cross-site scripting (XSS) vulnerability found in the Horde Groupware Webmail Edition.

What is CVE-2021-26929?

The vulnerability in Horde Groupware Webmail Edition through version 5.2.22 allows attackers to bypass XSS defenses by encoding JavaScript within email messages, leading to potential script execution on the victim's side.

The Impact of CVE-2021-26929

This vulnerability could be exploited by malicious actors to launch script-based attacks on users of Horde Groupware Webmail Edition, potentially leading to sensitive information disclosure or unauthorized access.

Technical Details of CVE-2021-26929

This section outlines the specific technical aspects of the CVE.

Vulnerability Description

The XSS issue arises from mishandling JavaScript encoded as a link or email in plain text messages, affecting the preProcess function in Text2html.php.

Affected Systems and Versions

Horde Groupware Webmail Edition versions through 5.2.22 are impacted, specifically when using the Horde_Text_Filter library before version 2.3.7.

Exploitation Mechanism

Attackers exploit the XSS vulnerability by embedding JavaScript code within email messages, taking advantage of the bespoke handling of certain characters that interferes with XSS defenses.

Mitigation and Prevention

Protecting systems from CVE-2021-26929 involves immediate actions and long-term security practices.

Immediate Steps to Take

Update Horde Groupware Webmail Edition to version 5.2.23 or above, where the XSS vulnerability is patched.
Educate users about the risks of clicking on links or downloading attachments from unknown or suspicious sources.

Long-Term Security Practices

Implement content security policies (CSP) to mitigate the risks of XSS attacks across web applications.
Regularly monitor and audit email content for suspicious or malicious payloads.

Patching and Updates

Stay informed about security updates and patches released by Horde Groupware to address vulnerabilities promptly.