Threat Hunting for CVE-2019–19781

CVE-2019–19781 is a critical vulnerability affecting Citrix Application Delivery Controller (ADC) and Gateway (previously known as Netscaler ADC and Gateway). The vulnerability allows unauthenticated remote attackers to execute arbitrary code on vulnerable systems. This threat hunting package aims to proactively identify potential exploitation attempts and compromised systems related to CVE-2019–19781 within the organization’s network.

MITRE ATT&CK Tactics and Techniques:
Tactics: Initial Access, Execution, Persistence, Privilege Escalation
Techniques: T1190 Exploit Public-Facing Application (CVE-2019–19781)
T1059 Command and Scripting Interpreter (Potential payload execution)

The threat involves malicious actors attempting to exploit the CVE-2019–19781 vulnerability in Citrix ADC and Gateway devices. Once successfully exploited, attackers can gain unauthorized access to the affected system, execute arbitrary commands or code, and establish persistence to maintain control over the compromised device. Depending on the attacker’s intent, they may further escalate privileges to move laterally or exfiltrate sensitive data.

Mitigation Recommendations:
- Apply the latest security patches and updates for Citrix ADC and Gateway devices.
- Implement network segmentation to limit the impact of potential compromises.
- Employ strong authentication mechanisms to reduce the risk of unauthorized access.
- Regularly monitor and audit network traffic for suspicious activities.

Below are some Splunk queries that can be used for threat hunting related to CVE-2019–19781:

Identify Potential Exploitation Attempts:

index=your_index sourcetype=your_sourcetype (source=your_web_logs OR source=your_firewall_logs)
(CVE-2019–19781 OR “Citrix ADC” OR “Netscaler ADC” OR “Citrix Gateway” OR “Netscaler Gateway”)
| stats count by source_ip, dest_ip, host, sourcetype, source
| sort — count

Detect Suspicious Command Execution:

index=your_index sourcetype=your_sourcetype (source=your_web_logs OR source=your_firewall_logs)
(CVE-2019–19781 OR “Citrix ADC” OR “Netscaler ADC” OR “Citrix Gateway” OR “Netscaler Gateway”)
(“cmd.exe” OR “powershell.exe” OR “/bin/bash” OR “/bin/sh” OR “/bin/nc”)
| stats count by source_ip, dest_ip, host, sourcetype, source, user
| sort — count

Look for Web Shell Activity:

index=your_index sourcetype=your_sourcetype (source=your_web_logs OR source=your_firewall_logs)
(CVE-2019–19781 OR “Citrix ADC” OR “Netscaler ADC” OR “Citrix Gateway” OR “Netscaler Gateway”)
(“cmd.exe” OR “powershell.exe” OR “/bin/bash” OR “/bin/sh” OR “/bin/nc”)
| rex field=_raw “(?<webshell>cmd.exe|powershell.exe|/bin/bash|/bin/sh|/bin/nc)”
| stats count by source_ip, dest_ip, host, sourcetype, source, webshell
| sort — count

Note: Make sure to replace `your_index`, `your_sourcetype`, and `your_web_logs`/`your_firewall_logs` with the appropriate values from your Splunk environment.

Remember that threat hunting is an ongoing process, and the queries mentioned above may need to be adjusted based on your specific environment and threat landscape. Additionally, it’s crucial to keep your knowledge base updated with the latest security research and indicators of compromise related to CVE-2019–19781.

References:

- CVE-2019–19781: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-19781
- Citrix Security Bulletin: https://support.citrix.com/article/CTX267027