Falcon Zero-Day Flash Detection

In the wake of the Hacking Team leaks in early July, a result of an intrusion into the company’s network, various zero-day vulnerabilities that affect multiple platforms and software configurations were exposed to the public. Vulnerabilities provided to vendors through responsible disclosure mechanisms allow vendors to patch these vulnerabilities before they are exploited in the wild; however in cases such as the Hacking Team leaks, vendors have little chance to patch vulnerabilities before they are exploited by criminal gangs, hacktivists and state sponsored actors.

The Hacking Team example is particularly damaging, as the zero-day vulnerabilities included well documented proof of concepts that are quickly and easily integrated into an attacker's arsenal. When taking into consideration the large arsenal of zero-day vulnerabilities that are currently being sold or exploited by similar companies, we can see that this threat is even greater.

In the case of the leaks, Adobe Flash exploits for CVE-2015-5119, CVE-2015-5122 and CVE-2015-5123 were seen in the wild within days of the Hacking Team leak, well before Adobe was able to patch the vulnerabilities.

These exploits were linked to Chinese state-sponsored actors, as well as used in public exploit kits employed by criminal actors. Through CrowdStrike's focus on effect-based Indicators of Attack (IoA), as opposed to Indicators of Compromise (IoC) signatures, we are not reliant on engaging in the constant arms race that is required to detect and prevent the exploitation of new vulnerabilities and discover IoCs used by adversaries.

This blog provides an example of how Falcon in conjunction with the CrowdStrike Security Operations Center (Falcon Overwatch) was able to detect and disrupt exploitation of our customer base from zero-day Adobe Flash exploits exposed in the Hacking Team leaks. These detections occurred both before and after patches were released for these vulnerabilities in Adobe Flash. The data produced by the Falcon sensor is used extensively by Falcon Overwatch to discover adversary activity using an IoA detection approach. Soon after the Hacking Team leaks, Falcon Overwatch was alerted to an IoA designed to detect exploitation of the Flash plugin within a browser context. The team then observed use of the exploitation, and was able to defeat the attacker as they started to perform network reconnaissance.

Upon exploitation, CrowdStrike observed attackers delivering different malware payloads. Among these were PlugX, Emdivi and IsSpace, all of which are linked to Chinese targeted intrusion operators. In this case the payloads would be dropped in the form of a binary called rdws.exe. A handful of reconnaissance commands were then executed by rdws.exe. These commands were executed in a time frame that indicated that the attackers were hands on keyboard, rather than automated network reconnaissance. For further analysis we can look to our Endpoint Activity Monitoring (EAM) system. EAM provides an instant indexed search for all real-time and historical execution events monitored by Falcon.

Performing a search for the SHA256 hash for rdws.exe reveals a number of other interesting details in relation to its execution. After execution, rdws.exe was moved to the C:\ProgramData directory and renamed to wmiprivse.exe. Persistence was obtained through the common \Software\Microsoft\Windows\CurrentVersion\Run registry entry using the reg object name of adobeUpdate. With the prompt alert from CrowdStrike, the customer immediately acted to prevent any negative impact to the organization from attacker activity. Additional analysis revealed the the Flash exploit used to carry out this attack was CVE-2015-5122. The other hosts that were exploited in a similar manner had a binary written to disk with the same filename, but different hash and behavior. Below is a process tree showing the execution of another rdws.exe sample detected at a different customer. A final instance shows attackers successfully exploiting Flash and once again being halted before the accomplishment of their objectives.

Hashes for malicious rdws.exe delivered via these flash exploits

Malicious adobe.dat dropped by rdws.exe in several instances

Zero-days prove to be difficult and often impossible to detect using signature-based IOCs.

Maintaining a blacklist of known malicious domains hosting a Flash exploit may allow you to detect potentially infected hosts, but what happens when hosts are infected by a domain that is not known to be malicious? As we’ve demonstrated in this example, the capability to use IOAs to monitor a browser for suspicious Flash behavior allows you to mitigate both zero-day and known Flash exploits. In conclusion, an IOA-based approach that looks at the effects of the execution activity independent of the vulnerability or exploit used is highly effective.