Secure Your Network: How Attackers Exploit Stolen Logins on SonicWall VPNs
Secure Sockets Layer (SSL) Virtual Private Networks (VPNs) are a cornerstone of modern business, providing secure remote access to critical internal resources. However, a recent wave of sophisticated cyberattacks demonstrates that even trusted security appliances like SonicWall SSL VPNs can become a gateway for intruders if not properly configured and monitored.
Threat actors are actively targeting these devices, not by exploiting a software vulnerability, but by using a much simpler and often overlooked entry point: legitimate, stolen user credentials. This tactic allows them to bypass perimeter defenses and appear as valid users, making their malicious activity incredibly difficult to detect.
The Attack Chain: From Login to Network Compromise
Understanding how these attacks unfold is the first step toward building a stronger defense. The process is methodical and designed to evade initial detection.
Initial Access Through Stolen Credentials: The entire attack hinges on attackers first obtaining valid usernames and passwords. These are typically acquired through phishing campaigns, information-stealing malware, or by purchasing them from dark web marketplaces where credentials from previous data breaches are sold.
Legitimate VPN Login: Armed with valid credentials, the attacker simply logs into the organization’s SonicWall SSL VPN portal. To firewalls and basic logging systems, this activity appears as a normal, authorized user session, raising no immediate alarms.
Network Reconnaissance and Lateral Movement: Once inside the network perimeter, the attackers begin their exploration. They use common, legitimate IT tools to map the network, identify high-value targets like domain controllers and file servers, and understand the internal architecture. This “living off the land” technique uses tools already present on the network, such as
net.exeandping.exe, to avoid triggering security alerts.Deployment of Malicious Tools: After identifying key systems, the attackers deploy remote access tools (RATs) to establish persistent control. Tools like ScreenConnect (now ConnectWise Control) and other remote desktop software are often used to maintain a foothold within the compromised network.
Data Exfiltration and Ransomware: The ultimate goal is often twofold: steal sensitive corporate data and deploy ransomware to encrypt critical systems. By this stage, the attackers have deep access to the network, and the potential for significant financial and reputational damage is extremely high.
Why This Threat Is So Critical
This attack method is particularly dangerous because it subverts traditional security measures. Your firewall and intrusion prevention systems may not flag the initial login because, technically, nothing improper occurred—a valid user logged in with a valid password.
The core issue is the reliance on single-factor authentication (passwords alone). In today’s threat landscape, a password should be considered a weak and easily compromised form of verification.
Actionable Steps to Protect Your SonicWall VPN
Protecting your organization requires a layered defense strategy focused on identity and access management. Simply relying on the VPN device itself is no longer sufficient.
Mandate Multi-Factor Authentication (MFA): This is the single most effective defense against credential-based attacks. By requiring a second form of verification—such as a code from a mobile app or a physical security key—you ensure that a stolen password alone is useless to an attacker. If you do nothing else, enable MFA on your VPN immediately.
Implement Geolocation and IP Restrictions: If your employees only operate within a specific country or region, configure your VPN to block login attempts from other parts of the world. You can also restrict access to known, trusted IP addresses to further shrink your attack surface.
Actively Monitor VPN Logs: Don’t let your logs sit unexamined. Regularly review them for suspicious patterns, such as:
- Logins from unusual or multiple geographic locations in a short time (“impossible travel”).
- Multiple failed login attempts followed by a success from an unfamiliar IP address.
- Logins occurring at odd hours (e.g., 3 AM on a weekend).
Enforce Strong Password Policies and User Education: Continue to enforce the use of long, complex, and unique passwords. More importantly, train your employees to recognize phishing attempts and understand the importance of never reusing passwords across different services.
The Bottom Line: Security Beyond the Perimeter
The security of your network is no longer just about building a strong wall. This campaign targeting SonicWall VPNs highlights a critical shift in cybersecurity: the battle has moved from the network perimeter to the user identity.
Organizations must assume that user credentials will eventually be compromised. By implementing robust security controls like Multi-Factor Authentication and maintaining vigilant monitoring, you can create a resilient defense that protects your critical assets even when the front door is unlocked with a stolen key. Review your VPN security posture today before it becomes an entry point for a devastating breach.
Source: https://securityaffairs.com/183245/hacking/attackers-exploit-valid-logins-in-sonicwall-ssl-vpn-compromise.html
