Security researchers have publicly disclosed a proof-of-concept (PoC) exploit for CVE-2025-21333, a critical elevation-of-privilege vulnerability in Microsoft’s Hyper-V virtualization framework.
The vulnerability resides in the vkrnlintvsp.sys driver and enables local attackers to gain SYSTEM privileges through a sophisticated heap manipulation technique.
Microsoft rated this flaw as Important (7.8 CVSSv3) in its January 2025 advisory.
Vulnerability Overview
According to a GitHub report, the vulnerability stems from a heap-based buffer overflow (CWE-122) in the NT Kernel & System component of Hyper-V’s virtualization service provider.
Attackers can exploit this flaw by crafting malicious I/O Request Packet (IRP) operations that overwrite critical memory structures in the Windows paged pool. Successful exploitation allows:
- Arbitrary read/write capabilities in kernel memory
- Direct manipulation of process tokens
- Privilege escalation from standard users to SYSTEM
The exploit leverages Windows I/O Rings, a high-performance I/O mechanism introduced in Windows 11 22H2.
By manipulating the _IOP_MC_BUFFER_ENTRY structures associated with I/O Rings, attackers can redirect kernel operations to user-controlled memory regions.
Exploit Mechanism
The PoC demonstrates a novel technique involving:
- Pool grooming: Allocating/Freeing IrRB (I/O Ring Buffer) pool chunks
- Controlled overflow: Triggering the vulnerability to overwrite adjacent pool allocations
- Memory redirection: Replacing legitimate _IOP_MC_BUFFER_ENTRY pointers with attacker-controlled addresses
Key code snippet from the PoC (simplified):
// Overwrite IOP_MC_BUFFER_ENTRY array pointer
BuildIoRingWriteFile(
hIoRing,
malicious_entry_ptr, // User-space fake buffer entry
target_process_token,
sizeof(TOKEN),
0,
FILE_WRITE_FLAGS_NONE
);This technique bypasses previous mitigations by avoiding NtQuerySystemInformation for address leaks and maintaining full control through I/O Ring operations.
The attacker subsequently modifies the tokenPrivileges field of the SYSTEM process’s _TOKEN structure to achieve privilege escalation.
Impact Assessment
Microsoft confirmed active exploitation in the wild before the patch release. Affected systems include:
- Windows 11 23H2 (confirmed)
- Windows 11 24H2 (suspected)
- Any Hyper-V-enabled environments
Successful exploitation requires low-privileged access and specific configurations:
- Windows Sandbox feature enabled
- Working with 0x50-byte pool allocations
- Vulnerable versions of vkrnlintvsp.sys (SHA256: 28948C65EF108AA5B43E3D10EE7EA7602AEBA0245305796A84B4F9DBDEDDDF77)
Security practitioners should prioritize patching due to the exploit’s:
- 100% reliability in controlled environments
- Lack of crash dumps in successful cases
- Ability to chain with other vulnerabilities
Workarounds for unpatched systems:
# Disable vulnerable driver via PowerShell
Disable-WindowsOptionalFeature -Online -FeatureName “Containers-DisposableClientVM”
Microsoft’s Security Response Center (MSRC) is investigating potential connections to:
- DarkHydrus operations in Southeast Asia
- Recent Azure VM credential theft campaigns
- Possible exploitation vectors in Windows Containers
Security teams should:
- Monitor for IrRB/NpAt pool tag allocations
- Block execution of binaries with known PoC hashes
- Audit SYSTEM token modifications via EDR solutions
The CVE-2025-21333 PoC demonstrates significant advancements in Windows kernel exploitation techniques.
By combining I/O Ring manipulation with precise pool grooming, attackers achieve reliable privilege escalation without traditional address-leak methods.
This vulnerability underscores the critical need for memory-safe practices in kernel-level development and proactive patch management in enterprise environments.
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 exploit for CVE-2025-21333, a critical elevation-of-privilege vulnerability in Microsoft's Hyper-V virtualization framework.){kind=link}