CVE-2024-1305: OpenVPN TAP-Windows6 Buffer Overflow Flaw

CVE-2024-1305 Overview

CVE-2024-1305 is an Integer Overflow vulnerability affecting the OpenVPN tap-windows6 driver version 9.26 and earlier. The driver fails to properly validate the size data of incoming write operations, allowing an attacker to overflow memory buffers. This can result in a bug check (Blue Screen of Death) and potentially arbitrary code execution in kernel space.

Critical Impact

This vulnerability enables remote attackers to execute arbitrary code with kernel-level privileges on Windows systems running vulnerable versions of the tap-windows6 driver, potentially leading to complete system compromise.

Affected Products

• OpenVPN tap-windows6 version 9.26 and earlier
• Windows systems using the tap-windows6 virtual network adapter
• OpenVPN deployments utilizing the vulnerable TAP driver

Discovery Timeline

• 2024-07-08 - CVE-2024-1305 published to NVD
• 2025-08-22 - Last updated in NVD database

Technical Details for CVE-2024-1305

Vulnerability Analysis

The tap-windows6 driver is a virtual network adapter component used by OpenVPN to create TAP (network tap) interfaces on Windows systems. This driver operates at the kernel level, handling network packet data between user-space applications and the network stack.

The vulnerability stems from inadequate size validation when processing write operations. When the driver receives incoming write requests, it fails to properly check the size parameter against expected bounds. This oversight allows an attacker to supply maliciously crafted size values that trigger an integer overflow condition.

When the integer overflow occurs, the driver allocates an insufficient buffer but proceeds to write data based on the original (overflowed) size value. This leads to a classic heap or pool buffer overflow in kernel memory, corrupting adjacent memory structures and potentially allowing an attacker to gain arbitrary code execution in kernel space.

Root Cause

The root cause is CWE-190: Integer Overflow or Wraparound. The tap-windows6 driver does not perform adequate bounds checking on size parameters for incoming write operations. When an attacker provides a size value that causes an integer overflow during buffer allocation calculations, the resulting buffer is smaller than expected, but subsequent write operations use the original size value, causing memory corruption beyond the allocated buffer boundaries.

Attack Vector

The attack can be initiated over the network against systems with the vulnerable tap-windows6 driver installed. An attacker can craft malicious network packets or write requests with specially designed size parameters that trigger the integer overflow. The network-accessible nature of this vulnerability, combined with no authentication requirements and low attack complexity, makes it particularly dangerous for exposed systems.

The exploitation flow involves:

1. Identifying a target system running the vulnerable tap-windows6 driver
2. Sending crafted write operations with malicious size parameters
3. Triggering the integer overflow to cause buffer overflow in kernel memory
4. Achieving arbitrary kernel code execution or system crash (BSOD)

Detection Methods for CVE-2024-1305

Indicators of Compromise

• Unexpected Blue Screen of Death (BSOD) errors referencing tap0901.sys or related TAP driver components
• Crash dumps indicating pool corruption or memory violations in the tap-windows6 driver
• Unusual network traffic patterns targeting OpenVPN TAP interfaces
• System event logs showing driver failures or unexpected kernel exceptions

Detection Strategies

• Monitor for crash events and bug checks involving the tap-windows6 driver (tap0901.sys)
• Implement endpoint detection rules to identify abnormal write operations to TAP driver interfaces
• Deploy network intrusion detection signatures for malformed packets targeting OpenVPN TAP adapters
• Use SentinelOne's behavioral AI to detect anomalous kernel-level activity associated with driver exploitation

Monitoring Recommendations

• Enable Windows Error Reporting and monitor for recurring tap-windows6 driver crashes
• Implement kernel-mode monitoring for suspicious memory allocation patterns
• Monitor OpenVPN logs for unusual connection attempts or malformed data
• Deploy SIEM rules to correlate network anomalies with endpoint driver events

How to Mitigate CVE-2024-1305

Immediate Actions Required

• Upgrade tap-windows6 driver to version 9.27 or later immediately
• Audit all Windows systems for the presence of vulnerable tap-windows6 driver versions
• Consider temporarily disabling OpenVPN TAP interfaces on critical systems until patching is complete
• Implement network segmentation to limit exposure of systems running the vulnerable driver

Patch Information

OpenVPN has released tap-windows6 version 9.27 which addresses this vulnerability. Users should update their TAP driver installations through the official OpenVPN distribution channels. For detailed patch information, refer to the OpenVPN CVE-2024-1305 Wiki and the OpenVPN Users Mailing List Post.

Workarounds

• Restrict network access to systems running the tap-windows6 driver using firewall rules
• Implement host-based intrusion prevention systems to monitor and block suspicious driver interactions
• Use SentinelOne's kernel-level protection to detect and prevent exploitation attempts
• Consider alternative VPN solutions if immediate patching is not feasible
• Disable unused TAP adapter interfaces to reduce attack surface

# Check installed tap-windows6 driver version on Windows
# Run in elevated PowerShell
Get-WmiObject Win32_PnPSignedDriver | Where-Object {$_.DeviceName -like "*TAP-Windows*"} | Select-Object DeviceName, DriverVersion

# Alternatively, check via device manager export
pnputil /enum-drivers | findstr /i "tap"