SONICWALL
ZERO-DAY
BreachNewsAugust 29, 20258 min read

VPN Breach for Sale: From SonicWall Zero-Day to Underground Markets

A recently disclosed zero-day vulnerability in SonicWall VPN appliances has become a significant attack vector, with threat actors selling unauthorized corporate network access on dark web forums.

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A recently disclosed zero-day vulnerability in SonicWall VPN appliances has become a significant attack vector for threat actors targeting enterprises across North America. This vulnerability allows remote attackers to gain unauthorized access to networks, even when Multi-Factor Authentication (MFA) is in place.

Active Threat

A threat actor operating under the alias "ProfessorKliq" posted on a dark web forum, offering unauthorized VPN access to 11 organizations based in the United States and Canada. These accesses appear tied to the SonicWall zero-day.

Industry Sectors Targeted

The listing outlines access to companies operating in a wide array of industries:

The presence of companies from industrial, critical infrastructure, and engineering domains increases the potential for intellectual property theft, production disruption, and downstream supply chain compromise.

Why the SonicWall VPN Zero-Day Matters

SonicWall VPNs are commonly deployed across mid-sized organizations and public sector environments. This specific zero-day vulnerability allows an attacker to bypass authentication entirely, resulting in undetectable compromise unless proactive monitoring is in place.

Business Risk

This is not just a firewall or VPN problem; it is a business risk issue. Access to internal networks is now a commodity on underground markets.

How Mjolnir Security Can Help

Mjolnir Security has been tracking these underground sales and the tactics used by threat actors like ProfessorKliq for years.

Stormbreaker Mobile DefenseDark Web MonitoringTHOR Compromise AssessmentsZero Trust Hardening24/7 Incident ResponseDFIR
  • Stormbreaker Mobile Defense Suite: Deploy Microsoft Intune with custom app protection policies to restrict device-level access, enforce secure VPN routing, and block unauthorized app installations.
  • Dark Web Monitoring and Actor Attribution: We monitor underground forums for your brand, domains, VPN endpoints, and credentials with takedown coordination.
  • Compromise Assessments Powered by THOR: Nextron THOR and internal threat-hunting frameworks to sweep your network for persistence mechanisms and malware beacons.
  • VPN and Zero Trust Hardening: SIEM-based alerting, network segmentation, and VPN reconfiguration to detect and prevent abuse.
  • 24/7 Incident Response and Forensics: Immediate DFIR support including triage, containment, forensic imaging, memory analysis, and breach reporting.

Next Steps for At-Risk Organizations

If your organization uses SonicWall VPN appliances, the time to act is now:

Final Thoughts

Access to internal networks is now a commodity. Threat actors like "ProfessorKliq" are monetizing VPN weaknesses in near-real time, offering access to corporate environments at scale. The attack surface has moved beyond endpoints — remote access platforms and misconfigured identity controls are now the primary targets.

Written by: Mjolnir Security  |  Published: August 29, 2025