Process Doppelgänging
Windows Transactional NTFS (TxF) was introduced in Vista as a method to perform safe file operations. (Citation: Microsoft TxF) To ensure data integrity, TxF enables only one transacted handle to write to a file at a given time. Until the write handle transaction is terminated, all other handles are isolated from the writer and may only read the committed version of the file that existed at the time the handle was opened. (Citation: Microsoft Basic TxF Concepts) To avoid corruption, TxF performs an automatic rollback if the system or application fails during a write transaction. (Citation: Microsoft Where to use TxF) Although deprecated, the TxF application programming interface (API) is still enabled as of Windows 10. (Citation: BlackHat Process Doppelgänging Dec 2017) Adversaries may leverage TxF to a perform a file-less variation of Process Injection called Process Doppelgänging. Similar to Process Hollowing, Process Doppelgänging involves replacing the memory of a legitimate process, enabling the veiled execution of malicious code that may evade defenses and detection. Process Doppelgänging's use of TxF also avoids the use of highly-monitored API functions such as NtUnmapViewOfSection, VirtualProtectEx, and SetThreadContext. (Citation: BlackHat Process Doppelgänging Dec 2017) Process Doppelgänging is implemented in 4 steps (Citation: BlackHat Process Doppelgänging Dec 2017): * Transact – Create a TxF transaction using a legitimate executable then overwrite the file with malicious code. These changes will be isolated and only visible within the context of the transaction. * Load – Create a shared section of memory and load the malicious executable. * Rollback – Undo changes to original executable, effectively removing malicious code from the file system. * Animate – Create a process from the tainted section of memory and initiate execution.
Контрмеры |
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| Контрмера | Описание |
|---|---|
| Process Doppelgänging Mitigation |
This type of attack technique cannot be easily mitigated with preventive controls or patched 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 process-loading mechanisms 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 Doppelgänging 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 (Citation: Beechey 2010) tools, like AppLocker, (Citation: Windows Commands JPCERT) (Citation: NSA MS AppLocker) or Software Restriction Policies (Citation: Corio 2008) where appropriate. (Citation: TechNet Applocker vs SRP) |
Обнаружение
Monitor and analyze calls to CreateTransaction, CreateFileTransacted, RollbackTransaction, and other rarely used functions indicative of TxF activity. Process Doppelgänging also invokes an outdated and undocumented implementation of the Windows process loader via calls to NtCreateProcessEx and NtCreateThreadEx as well as API calls used to modify memory within another process, such as WriteProcessMemory. (Citation: BlackHat Process Doppelgänging Dec 2017) (Citation: hasherezade Process Doppelgänging Dec 2017) Scan file objects reported during the PsSetCreateProcessNotifyRoutine, (Citation: Microsoft PsSetCreateProcessNotifyRoutine routine) which triggers a callback whenever a process is created or deleted, specifically looking for file objects with enabled write access. (Citation: BlackHat Process Doppelgänging Dec 2017) Also consider comparing file objects loaded in memory to the corresponding file on disk. (Citation: hasherezade Process Doppelgänging Dec 2017) 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.
Ссылки
- Microsoft. (n.d.). PsSetCreateProcessNotifyRoutine routine. Retrieved December 20, 2017.
- hasherezade. (2017, December 18). Process Doppelgänging – a new way to impersonate a process. Retrieved December 20, 2017.
- Liberman, T. & Kogan, E. (2017, December 7). Lost in Transaction: Process Doppelgänging. Retrieved December 20, 2017.
- Microsoft. (n.d.). When to Use Transactional NTFS. Retrieved December 20, 2017.
- Microsoft. (n.d.). Basic TxF Concepts. Retrieved December 20, 2017.
- Microsoft. (n.d.). Transactional NTFS (TxF). Retrieved December 20, 2017.
Связанные риски
Каталоги
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