Cybersecurity researchers have identified a coordinated credential-based campaign attacking enterprise VPN gateways, targeting authentication portals on Cisco and Palo Alto Networks infrastructure. Rather than exploiting software vulnerabilities, this campaign relies on automated credential probing and brute-force login attempts, putting corporate remote access at elevated risk.
The malicious activity was detected over a concentrated period in mid-December 2025, demonstrating a sharp surge in scripted login attempts. This reflects the increased threat focus on exposed VPN endpoints — which have become critical infrastructure for remote work and secure access in enterprises worldwide.
In this article, we break down the nature and scope of this campaign, what it means for enterprise VPN security, and how organizations can better defend their remote access infrastructure.
How the Credential Campaign Works
Unlike traditional exploits that leverage software bugs or zero-day vulnerabilities, this credential-based attack uses widely known adversary techniques — specifically:
Credential stuffing: Using lists of stolen usernames and passwords, often gathered from other breaches.
Password spraying: Trying a limited set of common passwords across many accounts to avoid automated lockouts.
These methods rely on scripted login attempts instead of direct exploitation of flaws in the VPN software.
GreyNoise Intelligence observed millions of automated sessions directed at both Palo Alto Networks GlobalProtect portals and Cisco SSL VPN endpoints. The campaign’s distinguishing features include:
Use of consistent browser-like user agents in the login attempts
Originating from a centralized IP space associated with a hosting provider
A high volume of repetitive authentication attempts over short periods (GreyNoise)
This activity reflects a broad scanning and brute-force effort rather than a targeted exploit of any specific vulnerability — but the impact can be just as damaging if credentials are weak or reused.
Scale and Impact of the Attack
Palo Alto GlobalProtect Targeting
During a 16-hour window, security sensors emulating GlobalProtect services saw approximately 1.7 million automated login sessions. Over 10,000 distinct IPs participated in attempts to access authentication portals, primarily geolocated in the United States, Pakistan, and Mexico.
Cisco SSL VPN Activity
Similar patterns were observed on Cisco SSL VPN endpoints. The number of unique attacking IPs jumped significantly — representing a marked deviation from baseline traffic — and exhibited coordinated use of tooling and infrastructure.
Though none of the observed activity exploited software vulnerabilities, the sheer volume and scale of login attempts increases the likelihood that weak or compromised credentials could succeed. Successful access would compromise networks, enabling data theft, internal access, lateral movement, and potential ransomware deployment.
Why Enterprise VPN Gateways Are Attractive Targets
Enterprise VPN gateways — like Palo Alto’s GlobalProtect and Cisco’s SSL VPN — serve as the main entry points for remote employees. Their exposure online makes them a tempting focus for attackers aiming to break into corporate networks.
Several factors compound their attractiveness:
Remote work proliferation: More VPN users means more potential login vectors.
Credential reuse habits: Users often reuse passwords across accounts, making credential stuffing effective.
Insufficient multi-factor authentication (MFA): Lack of MFA dramatically increases risk.
According to experts, attackers often favor login automation because it scales easily and can evade basic defensive filters if MFA or lockout policies are not configured appropriately.
Defensive Measures and Best Practices
Security professionals can take concrete steps to mitigate credential-based attacks on enterprise VPN infrastructure:
1. Enforce Strong Password and MFA Policies
Strong passwords combined with multi-factor authentication drastically reduce the efficacy of credential stuffing and brute-force attacks.
“The most effective defense against automated credential attacks is enforcing MFA wherever possible.” — Industry security expert (general consensus among analysts).
2. Monitor and Audit Edge Devices Regularly
Frequent auditing of VPN gateway logs helps identify unusual access patterns early and facilitates swift incident response.
3. Rate Limiting and Lockout Logic
Implement account lockouts or rate limiting on failed login attempts to slow down automated attacks and trigger alerts for security teams.
4. Block Known Malicious IPs and Use Threat Intelligence
Curated blocklists — especially those capturing IPs associated with credential campaigns — can reduce the attack surface significantly.
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Conclusion
The credential-based attack campaign targeting VPN gateways underscores the evolving threat landscape for enterprise remote access infrastructure. Without exploiting software flaws, threat actors can still gain access through persistent, automated credential attacks that prey on weak authentication practices.
Enterprises must strengthen their VPN security posture by combining strong authentication, proactive monitoring, and robust incident response procedures. With remote access now central to business operations, ensuring resilient VPN infrastructure is no longer optional — it is critical.
