CVE-2020-13998 : Security Advisory and Response

Citrix XenApp 6.5, when 2FA is enabled, allows a remote unauthenticated attacker to ascertain whether a user exists on the server. This vulnerability affects unsupported products.

Understanding CVE-2020-13998

When 2FA is enabled in Citrix XenApp 6.5, a security flaw allows attackers to determine user existence on the server.

What is CVE-2020-13998?

This CVE refers to a vulnerability in Citrix XenApp 6.5 that enables remote unauthenticated attackers to identify valid usernames on the server due to the 2FA error page behavior.

The Impact of CVE-2020-13998

Attackers can exploit this vulnerability to gather user information without authentication.
This issue affects products that are no longer supported by the maintainer.

Technical Details of CVE-2020-13998

This section provides more technical insights into the vulnerability.

Vulnerability Description

The vulnerability in Citrix XenApp 6.5 allows remote unauthenticated attackers to confirm user presence on the server by observing the 2FA error page's behavior.

Affected Systems and Versions

Product: Citrix XenApp 6.5
Versions: All versions with 2FA enabled

Exploitation Mechanism

Attackers can exploit this vulnerability by entering valid usernames and observing the server's response to determine user existence.

Mitigation and Prevention

Protect your systems from CVE-2020-13998 with the following steps:

Immediate Steps to Take

Disable 2FA if possible until a patch is available.
Monitor user authentication attempts for suspicious activity.

Long-Term Security Practices

Regularly update and patch software to prevent vulnerabilities.
Implement multi-factor authentication securely to enhance user verification.

Patching and Updates

Stay informed about security updates from Citrix and apply patches promptly to mitigate this vulnerability.