Finding and Fixing Vulnerabilities in Citrix Server Detection , a Medium Risk Vulnerability

With Notes on Remediation, Penetration Testing, Disclosures, Patching and Exploits

Contents

  • Vital information on this issue
  • Scanning For and Finding Vulnerabilities in Citrix Server Detection
  • Penetration Testing (Pentest) for this Vulnerability
  • Security updates on Vulnerabilities in Citrix Server Detection
  • Disclosures related to Vulnerabilities in Citrix Server Detection
  • Confirming the Presence of Vulnerabilities in Citrix Server Detection
  • False positive/negatives
  • Patching/Repairing this vulnerability
  • Exploits related to Vulnerabilities in Citrix Server Detection

Vital Information on This Issue
Vulnerabilities in Citrix Server Detection is a Medium risk vulnerability that is one of the most frequently found on networks around the world. This issue has been around since at least 1990 but has proven either difficult to detect, difficult to resolve or prone to being overlooked entirely.


Vulnerability Name: Citrix Server Detection
Test ID: 1701
Risk: Medium
Category: Backdoors
Type: Attack
Summary: We detected the remote server to be a Citrix server.

Citrix servers allow a Windows user to remotely obtain a graphical login and therefore act as a local user on the remote host.

NOTE: by default the Citrix Server application utilizes a weak 40 bit obfuscation algorithm (not even a true encryption). If the default settings have not been changed, there already exists tools which can be used to passively ferret userIDs and passwords as they traverse a network.

If this server is located within your DMZ, the risk is substantially higher, as Citrix necessarily requires access into the internal network for applications like SMB browsing, file sharing, email synchronization, etc.

Impact: If an attacker gains a valid login and password, he may be able to use this service to gain further access on the remote host or remote network. This protocol has also been shown to be vulnerable to a man-in-the-middle attack.
Solution: Disable this service if you do not use it. Also, make sure that the server is configured to utilize strong encryption.
CVE:

More Information: https://access.ca.gov/faq/Resolving_Common_Citrix_Errors.htm

https://docs.oracle.com/cd/E22662_01/E27305/html/Citrix-Disabling-Auto-Client-Detection.html

Nist NVD (CVSS):
CVSS Score:
For more information on this also issue see: http://www.securiteam.com/windowsntfocus/6G00L15BPC.html

Scanning For and Finding Vulnerabilities in Citrix Server Detection
Use of Vulnerability Management tools, like AVDS, are standard practice for the discovery of this vulnerability. The primary failure of VA in finding this vulnerability is related to setting the proper scope and frequency of network scans. It is vital that the broadest range of hosts (active IPs) possible are scanned and that scanning is done frequently. We recommend weekly. Your existing scanning solution or set of test tools should make this not just possible, but easy and affordable. If that is not the case, please consider AVDS.

Penetration Testing (pentest) for this Vulnerability
The Vulnerabilities in Citrix Server Detection is prone to false positive reports by most vulnerability assessment solutions. AVDS is alone in using behavior based testing that eliminates this issue. For all other VA tools security consultants will recommend confirmation by direct observation. In any case Penetration testing procedures for discovery of Vulnerabilities in Citrix Server Detection produces the highest discovery accuracy rate, but the infrequency of this expensive form of testing degrades its value. The ideal would be to have pentesting accuracy and the frequency and scope possibilities of VA solutions, and this is accomplished only by AVDS.

Security Updates on Vulnerabilities in Citrix Server Detection
For the most current updates on this vulnerability please check www.securiteam.com Given that this is one of the most frequently found vulnerabilities, there is ample information regarding mitigation online and very good reason to get it fixed. Hackers are also aware that this is a frequently found vulnerability and so its discovery and repair is that much more important. It is so well known and common that any network that has it present and unmitigated indicates "low hanging fruit" to attackers.

Disclosures related to this vulnerability
http://seclists.org/fulldisclosure/2005/Dec/830

Confirming the Presence of Vulnerabilities in Citrix Server Detection
AVDS is currently testing for and finding this vulnerability with zero false positives. If your current set of tools is indicating that it is present but you think it is probably a false positive, please contact us for a demonstration of AVDS.

False positive/negatives
The secret killer of VA solution value is the false positive. There was an industry wide race to find the most vulnerabilities, including Vulnerabilities in Citrix Server Detection ,and this resulted in benefit to poorly written tests that beef up scan reports by adding a high percentage of uncertainty. This may have sold a lot of systems some years ago, but it also stuck almost all VA solutions with deliberately inaccurate reporting that adds time to repairs that no administrator can afford. Beyond Security did not participate in this race to mutually assured destruction of the industry and to this day produces the most accurate and actionable reports available.

Patching/Repairing this Vulnerability
http://support.citrix.com/article/CTX133066

Vulnerabilities in Citrix Server Detection is a Medium risk vulnerability that is also high frequency and high visibility. This is the most severe combination of security factors that exists and it is extremely important to find it on your network and fix it as soon as possible.

Exploits related to Vulnerabilities in Citrix Server Detection
https://www.exploit-db.com/exploits/35180/
https://www.cvedetails.com/vulnerability-list/vendor_id-422/Citrix.html
https://www.blackhat.com/docs/us-14/materials/us-14-Brodie-A-Practical-Attack-Against-VDI-Solutions-WP.pdf

Please also visit www.securiteam.com to view any exploits available for this vulnerability, or search using "Vulnerabilities in Citrix Server Detection".


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