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How CVE-2026-58530 Works
CVE-2026-58530 is a critical heap-based buffer overflow vulnerability identified in the Windows Resilient File System (ReFS). ReFS is a modern file system introduced by Microsoft, designed to maximize data availability, scale efficiently to large data sets, and provide resilience against corruption. It is the default file system for Windows Server and is also available on Windows 10 and 11 for specific workloads. The vulnerability resides within the kernel-mode driver components responsible for handling ReFS metadata and file operations.
The flaw stems from improper input validation and insecure memory management practices when the ReFS driver processes certain file system operations. Specifically, when a user or a process triggers a particular sequence of operations—such as mounting a volume, reading a specially crafted file, or interacting with a malicious ReFS volume—the driver allocates a buffer on the heap to store data. Due to a boundary error, the driver does not correctly calculate the required buffer size or fails to validate the length of incoming data before copying it into the fixed-size heap buffer. An attacker can exploit this by supplying a specially crafted file or USB device that, when processed, writes data beyond the allocated buffer’s boundaries.
This heap corruption overwrites adjacent memory structures, including function pointers, object metadata, or saved return addresses. By carefully crafting the overflow data, an attacker can hijack the execution flow of the system. The vulnerability is triggered locally, meaning the attacker must have physical or local access to the machine, or the ability to place a malicious file on an accessible ReFS volume. However, due to ReFS often being used in enterprise environments with shared storage, the impact can be widespread. Successful exploitation grants the attacker the ability to execute arbitrary code with the highest privileges—typically at the SYSTEM or kernel level—leading to complete system compromise. The vulnerability is classified under CWE-122 (Heap-based Buffer Overflow) and has been assigned a CVSS v3.1 base score of 7.8 (High) by Microsoft, indicating a significant risk.
The vulnerability affects a wide range of Windows versions, including multiple builds of Windows 10 (1607, 1809, 21H2, 22H2), Windows 11 (24H2, 25H2, 26H1), and Windows Server (2016, 2019, 2022, 2025). Given its presence in the core file system driver, a successful attack can bypass many user-mode security controls, making it a high-priority issue for system administrators.
DailyCVE Form:
Platform: Windows 10/11/Server
Version: 1607-26H1, Server 2016-2025
Vulnerability : Heap Buffer Overflow
Severity: 7.8 High
date: 2026-07-14
Prediction: 2026-07-14 (Patch Tuesday)
What Undercode Say:
Analytics:
The vulnerability is highly critical due to its presence in a core kernel-mode driver (ReFS.sys). Successful exploitation provides SYSTEM-level code execution, making it a prime target for local privilege escalation attacks. Attack vectors include physical access (malicious USB) and local file drops. Enterprise environments using ReFS for large volumes or Hyper-V are at heightened risk.
Bash Commands & Codes:
- Check ReFS Volumes:
fsutil fsinfo volumeinfo X:
- Identify ReFS Driver Version:
Get-ItemProperty -Path "C:\Windows\System32\drivers\refs.sys" | Select-Object VersionInfo
- Verify Patch Status (Example for Windows 11 24H2):
Get-HotFix | Where-Object { $_.HotFixID -like "KB" } | Sort-Object InstalledOn
Exploit:
An attacker with physical access can plug in a specially crafted USB drive formatted with a malicious ReFS volume. Alternatively, a local user can execute a low-privilege binary that mounts a crafted ReFS VHD file or triggers specific IOCTL calls to the ReFS driver, overflowing the heap and executing shellcode to spawn a SYSTEM shell.
Protection:
- Apply Patches: Immediately install the July 2026 Patch Tuesday security updates from Microsoft.
- Restrict Physical Access: Limit physical access to critical servers and workstations.
- Block Untrusted USB: Use Group Policy to disable auto-mounting of new volumes.
- Application Control: Enforce application whitelisting (e.g., AppLocker) to prevent unauthorized binary execution.
Impact:
- Confidentiality: Full read access to all system files and user data.
- Integrity: Ability to modify system files, install backdoors, and alter security configurations.
- Availability: Potential for system crashes (BSOD) or complete system takeover, leading to denial of service.
- Lateral Movement: Compromised systems can be used as a pivot point for network-wide attacks.
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Sources:
Reported By: nvd.nist.gov
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