Rule Document 1:67007

Rule Category

INDICATOR-COMPROMISE -- Snort detected a system behavior that suggests the system has been affected by malware. That behavior is known as an Indicator of Compromise (IOC). The symptoms could be a wide range of behaviors, from a suspicious file name to an unusual use of a utility. Symptoms do not guarantee an infection; your network configuration may not be affected by malware, but showing indicators as a result of a normal function. In this case, attackers may be attempting to gain privileges and access other systems, spread influence, and make calls and commands with elevated access. The context of the traffic is important to determine intrusion; traffic from an administration utility performing commands on a user's computer is likely not a compromise, but a user laptop accessing a webserver may indicate intrusion.

Alert Message

INDICATOR-COMPROMISE Citrix Netscaler webshell access attempt

Rule Explanation

This rule looks for HTTP requests that target webshells dropped into Netscaler appliances under the "vpn/theme/" URI. Successful exploitation can lead to unauthorized execution of malicious scripts via the planted webshell.

What To Look For

This rule fires on attempts to access webshells dropped in the Netscaler vpn theme directory.

Known Usage

Attacks/Scans seen in the wild

False Positives

No known false positives

Contributors

Cisco Talos Intelligence Group