Citrix releases final patches for critical CVE-2019-19781 security flaw

Citrix has finally released the last permanent fixes for the CVE-2019-19781 security flaw for version 10.5 of the Citrix Application Delivery Controller (ADC). The company now claims to have released permanent fixes for all supported versions of ADC, Gateway and SD-WAN WANOP.

Citrix has urged organisations to "patch immediately" - presumably, over the weekend. The flaw enables remote, unauthenticated attackers to perform arbitrary code execution, with exploits already having been detected in the wild. 

Citrix has now released the full range of fixes for CVE-2019-19781. Patch immediately and read @CISAgov's updated Alert at https://t.co/VVy6NlOFlp for more information. #Cyber #Cybersecurity #InfoSec

— US-CERT (@USCERT_gov) January 24, 2020

Indeed, German automotive parts maker Gedia was taken down with ransomware over the past week, with security researchers warning that the attackers cracked the company's network via vulnerable Citrix devices.

And there is evidence of sophisticated threat actors switching their attention from Pulse Secure VPNs, which was purportedly the entry point for the Travelex ransomware attackers, to Citrix appliances exploiting CVE-2019-19781.

The vulnerability affects the following Citrix appliances, according to the US-CERT advisory:

• Citrix NetScaler ADC and NetScaler Gateway version 10.5 - all supported builds;
• Citrix ADC and NetScaler Gateway version 11.1 - all supported builds before 11.1.63.15;
• Citrix ADC and NetScaler Gateway version 12.0 - all supported builds before 12.0.63.13;
• Citrix ADC and NetScaler Gateway version 12.1 - all supported builds before 12.1.55.18;
• Citrix ADC and Citrix Gateway version 13.0 - all supported builds before 13.0.47.24;
• Citrix SD-WAN WANOP appliance models 4000-WO, 4100-WO, 5000-WO, and 5100-WO - all supported software release builds before 10.2.6b and 11.0.3b. (Citrix SD-WAN WANOP is vulnerable because it packages Citrix ADC as a load balancer).

I examined the files #REvil posted from https://t.co/3wfGoNUqp4 after they refused to pay the #ransomware.

the interesting thing I discovered is that they obviously hacked Gedia via the #Citrix exploit

my bet is that all recent targets were accessed via this exploit.

(1/2) pic.twitter.com/tWeUR7I1zj

— Under the Breach (@underthebreach) January 24, 2020

But the weekend's work won't be completed after the patches have been installed and systems restarted.

Users have been advised to scan their networks for evidence of compromise after patching to ensure that their networks have not been cracked, with attackers leaving behind the tools to enable them to exploit their systems later. Citrix and FireEye have released a free Indicator of Compromise tool to help users.

Further reading

Dutch NCSC: Turn off Citrix ADC and Gateway servers NOW as mitigation measures are not effective

• Security
• 17 January 2020

Citrix and FireEye release free scanner to detect breached Citrix appliances

• Security
• 23 January 2020

Citrix releases permanent fixes for CVE-2019-19781 security flaw in Citrix ADC 11.1 and 12

• Security
• 20 January 2020

Citrix to release 'thoroughly tested' fixes for CVE-2019-19781 security flaw by the end of January

• Threats and Risks
• 13 January 2020

Citrix up for sale, claims report

• Mergers and Acquisitions
• 14 March 2017

Hackers are searching for Citrix servers vulnerable to remote code execution flaw, security researchers warn

• Security
• 09 January 2020

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• Topics
• Security
• Cloud and Infrastructure
• Security
• Citrix
• CVE-2019-19781
• NetScaler Gateway
• Citrix ADC
• SD-WAN WANOP
• Application Delivery Controller