Hvci Bypass

Understanding HVCI Bypasses: The Battle for Kernel Integrity

  • Bring Your Own Vulnerable Driver (BYOVD) attacks become trivial to detect and block.
  • Kernel shellcode execution is dead.
  • Persistence mechanisms that rely on kernel hooks (SSDT, IDT, IRP hooks) fail.
  1. Locate a function pointer inside a legitimate, read-only driver (e.g., a callback array for IRP dispatch).
  2. Using a signed vulnerable driver that allows arbitrary writes, overwrite that function pointer to point to a legitimate, existing executable function that does the attacker’s bidding (e.g., ExQueueWorkItem to run code in a different context).

There are several methods to bypass HVCI, but it's essential to note that these methods may be complex, potentially illegal, and can have significant implications: Hvci Bypass

1. Data-Only Attacks The most common method for bypassing HVCI is the "Data-Only" attack. Since HVCI prevents the execution of new code (shellcode), attackers shift their focus to manipulating existing code. Instead of injecting a malicious payload, an attacker with kernel read/write capabilities (obtained via a BYOVD exploit) will target critical data structures. For example, an attacker might target the Token property of a process object to elevate privileges. By swapping the token of a low-privilege process with that of a SYSTEM process, the attacker achieves their goal without ever injecting executable code. Because the attacker is only modifying data pointers—not executing unsigned code—HVCI’s strict code integrity policies are not triggered. Understanding HVCI Bypasses: The Battle for Kernel Integrity

  • Arbitrary memory writes via vulnerable signed drivers: exploit a signed driver with a write-what-where to patch kernel structures or hook function pointers without adding new executable pages.
  • Object and pointer hijacking: corrupting kernel-managed objects or pointers that the hypervisor doesn’t explicitly validate.
  • Signed driver loading chains: use legitimate, signed drivers with permissive features to load secondary components that perform malicious actions.
  • Time-of-check time-of-use (TOCTOU) race exploitation: perform rapid swaps or remapping between check and execute.
  • Leveraging microarchitecture features: speculative execution and side channels sometimes enable leaking secrets or influencing checks indirectly (research area, complex).