Zeek Package that detects CallStranger (CVE-2020-12695) attempts (http://callstranger.com/)

This package attempts to detect CallStranger (CVE-2020-12695) exploitation attempts and data exfiltration. It does so by looking for three key things:

1. UPnP SUBSCRIBE commands 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
2. UPnP NOTIFY commands that are destined for a non-RFC1918 or local_nets address. This could indicate active DDoS amplification or Data Exfiltration
3. UPnP SUBSCRIBE commands with a Notify URL that is longer than CallStrangerDetector::exfiltration_threshold bytes. This could indicate data exfiltration over UPnP

The module assumes that your site doesn't normally have UPnP SUBSCRIBE or 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.

Usage

Standalone Mode

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

Notice Types

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

Configuration Options

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

Disclaimer

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!