CVE-2021-32537: Realtek HDA Driver DOS Vulnerability

CVE-2021-32537 Overview

CVE-2021-32537 is a driver vulnerability in the Realtek High Definition Audio (HDA) Driver. A local attacker with low privileges can send a crafted string to the kernel driver from user mode, triggering out-of-bounds memory access. The unexpected commands cause the kernel driver to crash, resulting in a system-wide denial of service. The vulnerability is tracked under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer) and affects the RTKVHD64.sys kernel-mode driver shipped with Realtek HDA audio packages.

Critical Impact
A local, low-privileged user can crash the Windows kernel through the Realtek HDA driver, producing a bug check (BSOD) and disrupting availability across the affected host.

Affected Products

Realtek HD Audio Driver (RTKVHD64.sys)
Systems shipping Realtek HDA audio components on Windows
OEM audio packages bundling the vulnerable Realtek kernel driver

Discovery Timeline

2021-07-07 - CVE-2021-32537 published to NVD
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-32537

Vulnerability Analysis

The flaw resides in the Realtek HDA kernel driver RTKVHD64.sys, which exposes an IOCTL interface to user-mode processes. The driver fails to validate input lengths and structure fields supplied by callers. When a user-mode process submits a specially crafted string through the device interface, the driver performs an out-of-bounds memory access in kernel space. The unexpected command corrupts kernel state and forces a bug check, halting the operating system.

The issue is exploitable from a standard user context because the device object is reachable without administrative privileges. The impact is limited to availability — confidentiality and integrity are not directly affected — but the scope changes because a crash in a kernel component impacts the entire host beyond the calling process.

Root Cause

The root cause is missing bounds validation on user-controlled input passed to the driver's IOCTL handlers. The driver trusts the caller-supplied buffer descriptors, dereferencing memory outside the allocated region. This maps to [CWE-119] and is consistent with the out-of-bounds access pattern described in the public Packet Storm advisory.

Attack Vector

Exploitation requires local access and the ability to open a handle to the Realtek HDA driver's device object. An attacker invokes DeviceIoControl with a malformed input buffer containing the trigger sequence. The driver dispatch routine processes the request without validating boundaries, producing a kernel access violation. No user interaction is required beyond running the malicious binary.

No verified public exploit code is available. Technical details are documented in the Packet Storm Security Advisory and the TWCERT Security Bulletin.

Detection Methods for CVE-2021-32537

Indicators of Compromise

Unexpected BugCheck events in the Windows System event log referencing RTKVHD64.sys as the faulting module.
Crash dump files in C:\Windows\Minidump\ containing a stack trace originating in the Realtek HDA driver.
Unsigned or unfamiliar user-mode processes opening handles to Realtek audio device objects shortly before a system crash.

Detection Strategies

Monitor Windows Error Reporting and kernel bug check codes (0x0000007E, 0x0000003B) where the faulting module is RTKVHD64.sys.
Audit process creation events for non-standard binaries issuing DeviceIoControl calls against Realtek HDA device paths.
Correlate repeated host crashes on systems running the same Realtek driver version to identify systemic exploitation attempts.

Monitoring Recommendations

Inventory all endpoints with RTKVHD64.sys and record installed driver versions for patch tracking.
Forward Windows kernel crash telemetry and minidump metadata to a centralized log platform for correlation.
Alert on EDR telemetry showing low-privileged processes opening handles to kernel audio devices followed by a system crash.

How to Mitigate CVE-2021-32537

Immediate Actions Required

Identify all hosts running the Realtek HDA driver and confirm the installed version of RTKVHD64.sys.
Apply the updated Realtek HDA driver supplied by Realtek or the system OEM as soon as it is available for the affected platform.
Restrict local logon rights on shared and multi-user systems until patching is complete.

Patch Information

Realtek has released updated HD Audio Driver packages addressing the out-of-bounds access. Coordinate updates through the OEM channel, since most Realtek HDA drivers are distributed by hardware vendors. Refer to the TWCERT Security Bulletin for vendor-coordinated remediation guidance.

Workarounds

Disable or uninstall the Realtek HDA driver on systems where audio functionality is not required.
Apply access control list restrictions on the driver's device object to limit which users can open handles to it.
Limit interactive logon to trusted administrators to reduce exposure of the local attack surface.

bash

# Query installed Realtek HDA driver version on Windows
pnputil /enum-drivers | findstr /I "Realtek"

# List loaded kernel driver and check file version
wmic datafile where name="C:\\Windows\\System32\\drivers\\RTKVHD64.sys" get Version