Description

Use after free in Windows Network Load Balancing allows an unauthorized attacker to execute code over a network.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.8",
  "pubDate": "2026-10-13T19:20:35.520Z",
  "pubdate": "2026-10-13T19:20:35.520Z",
  "executiveSummary": "A critical Use-After-Free (UAF) vulnerability exists within the Windows Network Load Balancing (NLB) driver, which manages traffic distribution across server clusters.\nThe vulnerability occurs due to improper memory management during the processing of network packets, leading to a state where the system attempts to access a memory location that has already been deallocated.\nAn unauthenticated, remote attacker can exploit this flaw by sending specially crafted packets to the target system. Successful exploitation allows for arbitrary code execution with kernel-level privileges, effectively compromising the integrity and availability of the host machine.\nThis vulnerability poses a significant risk as it can be triggered over the network without requiring prior authentication or user interaction. The impact includes full system takeover, potential data exfiltration, and lateral movement within the network infrastructure.\nThe flaw affects components responsible for cluster state synchronization and packet handling within the NLB driver. Organizations utilizing Windows NLB are at elevated risk and should prioritize monitoring and mitigation strategies.",
  "technicalDetails": "The root cause of this vulnerability lies in a race condition or logic error during the handling of network object references within the Windows Network Load Balancing (NLB) driver. In memory management, a Use-After-Free (UAF) occurs when a program continues to use a pointer after the memory area it references has been released to the heap. If the memory is subsequently reallocated for another object, the initial pointer may reference data controlled by an attacker.\nDuring normal NLB operations, the driver maintains internal structures to track cluster membership and traffic flow. When a specific sequence of malformed packets is received, the NLB component may prematurely release an object while an asynchronous task or concurrent thread still holds an active reference to it. The subsequent access to this dangling pointer facilitates the corruption of kernel memory structures.\nExploitation flow typically begins with an attacker identifying the network interface bound to the NLB service. The attacker transmits a series of malicious network frames designed to trigger the premature deallocation of a target object. Once the memory is freed, the attacker performs heap spraying or memory grooming—filling the heap with controlled data—to ensure that the reallocated memory block contains malicious payloads, such as function pointers or object vtables.\nWhen the vulnerable NLB driver attempts to use the dangling pointer, it inadvertently executes instructions or references data provided by the attacker. This redirection of execution flow allows for the hijacking of the kernel-mode instruction pointer. By crafting a sophisticated payload, the attacker can bypass security mitigations such as Kernel Address Space Layout Randomization (KASLR).\nBecause the NLB driver operates at a high privilege level (Ring 0), code execution at this stage bypasses user-mode security boundaries. The attacker can then elevate their privileges, install kernel-mode rootkits, or disable security software on the compromised host. The attack is particularly dangerous because it does not require authentication and is executed at the network level before reaching the higher-level OS networking stack or application logic, making it difficult to detect with traditional host-based firewalls."
}