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Process Hollowing

Process hollowing occurs when a process is created in a suspended state then its memory is unmapped and replaced with malicious code. Similar to Process Injection, execution of the malicious code is masked under a legitimate process and may evade defenses and detection analysis. [1] [2]

ID: T1093

Tactic: Defense Evasion

Platform:  Windows

Permissions Required:  User

Data Sources:  Process monitoring, API monitoring

Defense Bypassed:  Process whitelisting, Whitelisting by file name or path, Signature-based detection, Anti-virus

Version: 1.0

Examples

NameDescription
BADNEWS

BADNEWS has a command to download an .exe and use process hollowing to inject it into a new process.[3][4]

Bandook

Bandook has been launched by starting iexplore.exe and replacing it with Bandook's payload.[5][6]

BBSRAT

BBSRAT has been seen loaded into msiexec.exe through process hollowing to hide its execution.[7]

Cobalt Strike

Cobalt Strike can use process hollowing for execution.[8]

Duqu

Duqu is capable of loading executable code via process hollowing.[9]

Gorgon Group

Gorgon Group malware can use process hollowing to inject one of its trojans into another process.[10]

ISMInjector

ISMInjector hollows out a newly created process RegASM.exe and injects its payload into the hollowed process.[11]

menuPass

menuPass has used process hollowing in iexplore.exe to load the RedLeaves implant.[12]

Orz

Some Orz versions have an embedded DLL known as MockDll that uses process hollowing and Regsvr32 to execute another payload.[13]

Patchwork

A Patchwork payload uses process hollowing to hide the UAC bypass vulnerability exploitation inside svchost.exe.[14]

Smoke Loader

Smoke Loader spawns a new copy of c:\windows\syswow64\explorer.exe and then replaces the executable code in memory with malware.[15][16]

Mitigation

This type of attack technique cannot be easily mitigated with preventive controls since it is based on the abuse of operating system design features. For example, mitigating specific API calls will likely have unintended side effects, such as preventing legitimate software (i.e., security products) from operating properly. Efforts should be focused on preventing adversary tools from running earlier in the chain of activity and on identifying subsequent malicious behavior.

Although process hollowing may be used to evade certain types of defenses, it is still good practice to identify potentially malicious software that may be used to perform adversarial actions and audit and/or block it by using whitelisting [17] tools, like AppLocker, [18] [19] or Software Restriction Policies [20] where appropriate. [21]

Detection

Monitoring API calls may generate a significant amount of data and may not be directly useful for defense unless collected under specific circumstances for known bad sequences of calls, since benign use of API functions may be common and difficult to distinguish from malicious behavior. API calls that unmap process memory, such as ZwUnmapViewOfSection or NtUnmapViewOfSection, and those that can be used to modify memory within another process, such as WriteProcessMemory, may be used for this technique. [2]

Analyze process behavior to determine if a process is performing actions it usually does not, such as opening network connections, reading files, or other suspicious actions that could relate to post-compromise behavior.

References