Zeek Plugin that detects CallStranger (CVE-2020-12695) attempts (http://callstranger.com/)
This plugin attempts to detect CallStranger (CVE-2020-12695) exploitation attempts and data exfiltration. It does so by looking for three key things:
SUBSCRIBEcommands with a Notify URL that contains an IP address that isn't an RFC1918 or local_nets address. This could be the precursor for DDoS amplification or Data Exfiltration
NOTIFYcommands that are destined for a non-RFC1918 or local_nets address. This could indicate active DDoS amplification or Data Exfiltration
SUBSCRIBEcommands with a Notify URL that is longer than
CallStrangerDetector::exfiltration_thresholdbytes. This could indicate data exfiltration over UPnP
The module assumes that your site doesn't normally have UPnP
NOTIFY commands destined for the Internet and that you don't have UPnP devices exposed to the Internet. If either of these things are true, you will see false positives. You can add particular IPs that create false positives to the
CallStrangerDetector::ignore_subnets set to ignore them.
To use this script against a PCAP, simply clone the Git repository and run Zeek with
zeek -Cr your.pcap scripts/__load__.zeek
As a Package
To install the package, clone the Git repository and execute
zkg install . from the package directory
The module will add notices to
notice.log if it detects CallStranger-like activity. The notices are as follows:
CallStranger_Data_Exfiltration_Attempt: Observed an attempt to have a UPnP device exfiltrate traffic
CallStranger_Data_Exfiltration_Success: Observed a UPnP device likely exfiltrating data
CallStranger_UPnP_Request_Callback_To_External_Host: Observed an attempt to have a UPnP device call back to an external host
CallStranger_UPnP_To_External_Host: Observed a UPnP device calling back to an external host
There are three configuration options that you can set:
CallStrangerDetector::exfiltration_threshold: The number of bytes that need to be observed in a UPnP Callback URL in order to be classified as data exfiltration.
CallStrangerDetector::ignore_subnets: A set of subnets that should be ignored for UPnP detections. Use this if you have false positives where UPnP is traversing the Internet legitimately.
CallStrangerDetector::strict_upnp_protocol_detection: This boolean controls whether the script will be more strict when trying to identify UPnP SUBSCRIBE commands. It does so by requiring the “NT” (Notification Type) header to be observed. The default is false because the NT header doesn’t actually do anything, it’s just required by the UPnP specification. If you have non-UPnP SUBSCRIBE traffic, you may have to set this to true
I have tested this against local UPnP traffic and by using the proof of concept code provided by the CallStranger author (https://github.com/yunuscadirci/CallStranger). If you have any issues, please open a GitHub issue or contact us. Thanks!