Update: Critical Citrix Vulnerability Exploited

The Threat:

The eSentire Security Operations Center (SOC) has observed active exploitation of Citrix vulnerability CVE-2019-19781 to deliver cryptocurrency mining malware to vulnerable systems. At this time, eSentire has only seen CVE-2019-19781 exploited to install a cryptocurrency miner, but CVE-2019-19781 could be exploited for a wide variety of malicious purposes. Due to the ease of exploitation, lack of available security patches, and the observation of attacks against eSentire clients, the eSentire Threat Intelligence team recommends applying the mitigation actions provided by Citrix as soon as possible [1].

What we’re doing about it:

• esNETWORK rules identify the cryptocurrency miner in this campaign
• Known scanner and payload IP addresses have been added to the eSentire Global Black List
• MVS (formerly esRECON) has plugins to identify CVE-2019-19781
• esLOG customers have been reviewed for signs of Citrix ADC exploitation

What you should do about it:

• It is highly recommended that affected clients apply the mitigation actions provided by Citrix [1]
• See the TrustedSec blog post NetScaler Remote Code Execution Forensics for technical and investigation details [2]

Additional information

CVE-2019-19781 allows simple directory traversal by a remote attacker in Citrix Application Delivery Controller (ADC) and Gateway 10.5, 11.1, 12.0, 12.1, and 13.0. No patches have been made available at this time.

At this time, all activity identified by eSentire security teams has been related to deploying cryptocurrency miners. Associated indicators of compromise can be found below.

Event Timeline

Dec 16 - Vulnerability publicly disclosed by Citrix [3]

Dec 16 - Mitigation steps provided by Citrix [1]

Dec 23 - Positive Technologies comments on the potential impact of the vulnerability [4]

Dec 31 - SANS releases a speculative proof of concept [5]

Jan 8 - Active exploitation of honeypot environment observed by researcher Kevin Beaumont [6]

Jan 8 - Initial Citrix advisory was released by eSentire [7]

Jan 12 - Exploitation to deliver cryptocurrency mining malware was identified by eSentire

Expected Patch Release [8]