Security researcher Alessandro Iandoli has published a proof-of-concept (PoC) exploit for CVE-2025-21333, a zero-day vulnerability in Windows Hyper-V that has been actively exploited in attacks. The flaw, rated with a CVSS score of 7.8, enables attackers to gain SYSTEM privileges on affected Windows devices.
While details regarding real-world exploitation remain undisclosed, the vulnerability was anonymously reported and later patched by Microsoft in the January 2025 Patch Tuesday update. The PoC demonstrates an attack targeting the vkrnlintvsp.sys driver, leveraging an overwrite in the I/O Ring buffer entry to gain arbitrary read/write capabilities in the Windows kernel.
According to Iandoli, the exploit does not rely on traditional techniques such as NtQuerySystemInformation for leaking kernel addresses or PreviousMode for obtaining arbitrary read/write permissions. Instead, it takes advantage of a paged pool allocation technique involving _IOP_MC_BUFFER_ENTRY structures.
“The technique slightly differs from the one documented by Yarden Shafir,” Iandoli explains in his GitHub release. “Instead of taking control of the entire array pointed by _IORING_OBJECT.RegBuffers, the technique takes control only of one entry in the array pointed by _IORING_OBJECT.RegBuffers.”
This nuanced control allows for reliable arbitrary read/write operations, potentially enabling exploitation from heap overflows and use-after-free (UAF) vulnerabilities across multiple Low Fragmentation Heap (LFH) buckets. The researcher also highlights the ability to manipulate the size of the pointer array, further enhancing the exploit’s reliability.
The PoC requires enabling Windows Sandbox to trigger the vulnerable syscalls. Iandoli notes that while he achieved a 0xfff0-byte overflow, full control over the overflow length was not consistently achievable, leading to potential crashes if the overflow exceeds subsegment boundaries.
The exploit also relies on freeing and reallocating specific Windows Notification Facility (WNF) state data objects to achieve the desired memory layout. This process is susceptible to race conditions, where other drivers might allocate objects in the freed memory regions.
The PoC was tested successfully on Windows 11 23H2, and while it may function on Windows 11 24H2, this remains unverified.
Microsoft addressed CVE-2025-21333 in its January 2025 Patch Tuesday release. Windows users are strongly advised to apply the latest security updates to mitigate potential exploitation.
For security researchers and penetration testers interested in studying the CVE-2025-21333 vulnerability, Iandoli has made the PoC available on GitHub. However, given its complexity and potential for abuse, organizations should prioritize patching and implementing robust security measures to prevent exploitation.
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