CVE-2024-40764: SonicWall SonicOS DoS Vulnerability

CVE-2024-40764 Overview

A heap-based buffer overflow vulnerability exists in the SonicOS IPSec VPN component that allows an unauthenticated remote attacker to cause a Denial of Service (DoS) condition. This vulnerability affects the IPSec VPN implementation across multiple SonicWall firewall product lines, including the TZ, NSa, NSsp, and NSv series appliances.

The vulnerability stems from improper handling of memory buffers within the IPSec VPN processing logic, where specially crafted network packets can trigger a heap overflow condition, leading to service disruption or device crash.

Critical Impact

Unauthenticated remote attackers can exploit this vulnerability to disrupt VPN services and potentially cause widespread network connectivity issues for organizations relying on SonicWall firewalls for secure remote access.

Affected Products

• SonicWall SonicOS (multiple versions across product lines)
• SonicWall NSa Series: NSa 2700, NSa 3700, NSa 4700, NSa 5700, NSa 6700
• SonicWall NSsp Series: NSsp 10700, NSsp 11700, NSsp 13700, NSsp 15700
• SonicWall NSv Series: NSv 10, NSv 25, NSv 50, NSv 100, NSv 200, NSv 300, NSv 400, NSv 800, NSv 1600, NSv 270, NSv 470, NSv 870
• SonicWall TZ Series: TZ270, TZ270W, TZ370, TZ370W, TZ470, TZ470W, TZ570, TZ570P, TZ570W, TZ670

Discovery Timeline

• July 18, 2024 - CVE-2024-40764 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2024-40764

Vulnerability Analysis

This vulnerability is classified under CWE-122 (Heap-based Buffer Overflow) and CWE-787 (Out-of-bounds Write). The flaw exists in the IPSec VPN processing component of SonicOS, which is responsible for handling secure tunnel establishment and encrypted traffic processing.

When the IPSec VPN service processes incoming network packets, insufficient bounds checking on heap-allocated buffers allows an attacker to write data beyond the allocated memory region. This corruption of adjacent heap memory structures leads to unpredictable behavior, typically resulting in service termination or device reboot.

The attack is particularly concerning because it requires no authentication—any remote attacker with network access to the VPN service can attempt exploitation. The vulnerability is reachable via the network without user interaction, making it suitable for automated attack scenarios.

Root Cause

The root cause of this vulnerability is inadequate input validation and buffer size verification in the IPSec packet processing routines. When handling certain IPSec protocol messages, the code allocates a heap buffer based on expected data sizes but fails to properly validate actual incoming data lengths before copying data into the buffer.

This insufficient bounds checking allows oversized or malformed packet data to overflow the allocated heap buffer, corrupting heap metadata and adjacent memory allocations. The resulting heap corruption typically causes the IPSec service process to crash, denying VPN services to legitimate users.

Attack Vector

The attack vector for CVE-2024-40764 is network-based and requires no authentication or user interaction:

1. Reconnaissance: Attacker identifies SonicWall devices with exposed IPSec VPN services (typically UDP ports 500/4500 for IKE/NAT-T)
2. Packet Crafting: Attacker constructs malformed IPSec protocol packets designed to trigger the heap overflow condition
3. Exploitation: Malicious packets are sent to the target device's VPN service
4. Denial of Service: The heap overflow corrupts memory structures, causing the VPN service or entire device to crash

The attack does not require prior knowledge of VPN credentials or established sessions. Exploitation can be attempted against any SonicWall device with IPSec VPN functionality exposed to the attacker's network. While the current exploitation focus is DoS, heap-based buffer overflows may potentially be leveraged for more severe attacks such as code execution with further research.

Detection Methods for CVE-2024-40764

Indicators of Compromise

• Unexpected SonicWall device reboots or VPN service restarts without administrator action
• Anomalous IPSec/IKE traffic patterns with malformed or oversized packets to UDP ports 500/4500
• System logs indicating IPSec VPN process crashes or heap corruption errors
• Sudden loss of VPN connectivity affecting multiple remote users simultaneously

Detection Strategies

• Monitor SonicWall system logs for unexpected service restarts, crash dumps, or memory-related errors in IPSec components
• Implement network intrusion detection rules to identify malformed IPSec/IKE packets targeting SonicWall devices
• Deploy rate limiting and anomaly detection for UDP traffic to ports 500 and 4500 on firewall management interfaces
• Utilize SentinelOne Singularity platform for network traffic analysis and threat detection across endpoints connecting via affected VPN services

Monitoring Recommendations

• Configure SNMP or syslog monitoring to alert on device reboots and VPN service failures
• Establish baseline metrics for VPN session stability and alert on deviations indicating potential exploitation attempts
• Review firewall logs for repeated connection attempts from unknown sources to IPSec VPN services
• Implement SentinelOne Ranger to maintain visibility on network-connected SonicWall appliances and their operational status

How to Mitigate CVE-2024-40764

Immediate Actions Required

• Review the SonicWall Vulnerability Advisory SNWLID-2024-0012 for specific patched firmware versions and apply applicable updates immediately
• Restrict network access to IPSec VPN services to trusted IP ranges where feasible using access control lists
• Enable additional logging on SonicWall devices to capture detailed IPSec VPN activity for forensic analysis
• Consider temporarily disabling IPSec VPN functionality if not business-critical until patches can be applied

Patch Information

SonicWall has released patched firmware versions to address this vulnerability. Organizations should consult the SonicWall PSIRT Advisory SNWLID-2024-0012 for specific version information applicable to their hardware platform.

The advisory provides detailed guidance on affected versions and corresponding patched releases for each product line including TZ, NSa, NSsp, and NSv series appliances. Organizations should prioritize firmware updates based on device exposure and criticality.

Workarounds

• Implement network-level access controls to limit IPSec VPN exposure to known, trusted IP address ranges
• Deploy an external IPS/IDS solution capable of detecting and blocking malformed IPSec packets before they reach the firewall
• Consider using alternative VPN technologies (SSL VPN) if IPSec VPN can be temporarily disabled
• Enable geo-blocking to restrict VPN access from regions where legitimate users are not expected

# Example: Restrict IPSec VPN access at network perimeter (upstream router/firewall)
# Allow IPSec from trusted corporate IP ranges only
iptables -A INPUT -p udp --dport 500 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p udp --dport 4500 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p udp --dport 500 -j DROP
iptables -A INPUT -p udp --dport 4500 -j DROP