CVE-2025-3464-AsIO3-LPE

CVE-2025-3464: Unprivileged LPE exploit for ASUS AsIO3.sys - TOCTOU auth bypass + PreviousMode decrement

CVE-2025-3464: AsIO3.sys Local Privilege Escalation

This exploit will only work on Windows 11 22H2 or earlier. Microsoft fixed PreviousMode hijinks.

Local privilege escalation exploit for ASUS AsIO3.sys driver. Gets NT AUTHORITY\SYSTEM

Overview

This exploit chains an authentication bypass (CVE-2025-3464) with a decrement primitive to escalate privileges from any local user to SYSTEM.

Vulnerabilities

CVE-2025-3464 - Authentication Bypass via TOCTOU

The AsIO3.sys driver validates calling processes by checking if their executable path contains AsusCertService and verifying a SHA256 hash. This check is vulnerable to a Time-of-Check-Time-of-Use (TOCTOU) race condition using NTFS hardlinks.

Attack Flow:

1. Create hardlink at path containing AsusCertService pointing to exploit executable
2. Spawn child process via hardlink (process image path now passes substring check)
3. Swap hardlink to point to AsusCertService.exe
4. Child opens device handle
5. Authorization granted to attacker-controlled process

Note: The driver only checks if the path contains AsusCertService via substring match. Any user-writable path works (e.g., C:\Users\Public\AsusCertService\), making this exploitable without admin privileges.

Decrement Primitive (IOCTL 0xA0402450)

The driver exposes an IOCTL that calls ObfDereferenceObject on a user-controlled pointer. This performs an 8-byte atomic decrement at (ObjectPtr - 0x30), providing an arbitrary decrement primitive.

Exploitation via PreviousMode:

• Leak KTHREAD address via NtQuerySystemInformation(SystemHandleInformationEx)
• Target: KTHREAD + 0x232 (PreviousMode field)
• Decrement PreviousMode from 1 (UserMode) to 0 (KernelMode)
• With PreviousMode=0, NtReadVirtualMemory/NtWriteVirtualMemory can access kernel memory
• Walk EPROCESS list, steal SYSTEM token
• Restore PreviousMode to 1 before spawning shell

Usage

# Compile (Linux cross-compile)
x86_64-w64-mingw32-gcc -O2 -o AsIO3_FullExploit.exe AsIO3_FullExploit.c -lntdll -lshlwapi

On target (requires AsIO3.sys loaded)

AsIO3_FullExploit.exe

Prerequisites:

• AsIO3.sys driver loaded (comes with ASUS Armoury Crate, AI Suite, etc.)
• AsusCertService.exe accessible (searches common ASUS installation paths)

Structure Offsets (Windows 11 22H2)

KTHREAD + 0x232 = PreviousMode KTHREAD + 0x220 = Process (EPROCESS pointer) EPROCESS + 0x440 = UniqueProcessId EPROCESS + 0x448 = ActiveProcessLinks EPROCESS + 0x4B8 = Token

Note: Offsets are version-specific. Verify for your target Windows build. Windows 23H2 throws a PREVIOUS_MODE_MISMATCH (0x1f9). A mitigation for these previous mode tricks.

Technical Notes

• The 8-byte decrement at KTHREAD+0x232 affects adjacent fields (UserAffinityPrimaryGroup, BasePriority)
• Critical: PreviousMode MUST be restored to 1 before calling CreateProcess or any user-mode address space operations
• Failure to restore PreviousMode causes BSOD in nt!PspLocateInPEManifest during process creation

References

• https://blog.talosintelligence.com/decrement-by-one-to-rule-them-all/
• ASUS Armoury Crate / AI Suite driver components

Disclaimer

This code is provided for authorized security research and educational purposes only. Only use against systems you own or have explicit permission to test. Unauthorized access to computer systems is illegal.