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Covert Code Trying To Run in Memory is Blocked by New Sophos Protection Against “Heap-Heap” Permission Violations
March 2021 by Marc Jacob
Sophos revealed a new defense against adversaries trying to evade detection by loading fileless malware, ransomware and remote access agents into the temporary memory of compromised computers. In a new blog post, “Covert Code Faces a Heap of Trouble in Memory,” Sophos researchers detail how they discovered that covert attack code is injected directly into the dynamic “Heap” region of computer memory and then tries to obtain additional “Heap” memory with code execution rights, a behavior not seen in ordinary software. The researchers developed a new protection that is triggered whenever such “Heap-Heap” memory allocation behavior is detected.
The defense, called Dynamic Shellcode Protection, will make it significantly harder for adversaries to use memory as part of their arsenal of defense evasion techniques.
As Sophos recently reported in a series of articles on the realities of Conti ransomware, the memory of compromised computers is a popular hiding place for adversaries looking to conceal their presence from defenders while they load and execute the remote access agents that will serve as enablers for the rest of the attack. In the case of Conti, the remote access agent used was Cobalt Strike.
Dynamic Shellcode Protection is based on the fact that code such as applications are stored in memory regions that have “execution” rights. This enables the apps to run. However, the apps generally need some additional, temporary, in-memory workspace, for example to unpack or store data. This variable workspace is commonly called “Heap” memory. Apps can request their Heap memory allocation to come with execution rights.
In most cyberattacks, however, the loader for a remote access agent is injected directly into Heap memory. It then needs to obtain further executable memory from the Heap in order to accommodate the needs of the inbound remote access agent. This is referred to as “Heap-Heap” memory allocation behavior.
Sophos researchers realized that such behaviour was a clear indicator of potentially suspicious activity and designed a practical protection that blocks the allocation of execution permissions from one Heap memory to another. In doing so, the protection can intercept many cyberattacks involving remote access agents, fileless malware and ransomware, while being compatible with normal applications.
Dynamic Shellcode Protection is integrated into Sophos Intercept X.
General Advice for Defending Against Ransomware
• Shut down internet-facing remote desktop protocol (RDP) to deny cybercriminals access to networks
• If you need access to RDP, put it behind a VPN connection
• Use layered security to prevent, protect and detect cyberattacks, including endpoint detection and response (EDR) capabilities and managed response teams who watch networks 24/7
• Be aware of the five early indicators an attacker is present to stop ransomware attacks
• Have an effective incident response plan in place and update it as needed. If you don’t feel confident you have the skills or resources in place to do this, to monitor threats or to respond to emergency incidents, consider turning to external experts for help
