The digital frontier is constantly under siege, and the latest threat report paints a stark picture: a sophisticated network of Ukrainian-based autonomous systems has unleashed a significant wave of brute-force and password-spraying attacks. These campaigns are
specifically targeting critical enterprise remote access infrastructure, namely SSL VPN and RDP systems. This aggressive activity, observed between June and July 2025, involved hundreds of thousands of coordinated attacks
lasting up to three days, underscoring a persistent and evolving challenge for cybersecurity professionals globally.

Understanding the Threat: Brute-Force and Password-Spraying

While often used interchangeably, brute-force and password-spraying employ distinct methodologies to achieve similar goals: unauthorized access. A brute-force attack involves systematically trying every possible
combination of characters until the correct password is found. This is typically resource-intensive and can trigger lockout policies if not executed carefully. Conversely, password-spraying is a technique where
a small set of commonly used passwords (e.g., “Password123!”, “Summer2025”) is tried against a large number of user accounts. This method often bypasses lockout policies because each account only receives a few login attempts,
spreading the attack across a broader user base.

Targeted Systems: SSL VPN and RDP Protocols

The choice of SSL VPN and RDP as primary targets is not accidental. These protocols are the lifelines of remote work and network administration, offering direct access to internal enterprise networks and critical systems.
Compromising these entry points provides attackers with a significant foothold. SSL VPNs (Secure Sockets Layer Virtual Private Networks) encrypt and encapsulate network traffic, allowing remote users to securely connect
to a private network over the internet. RDP (Remote Desktop Protocol) enables users to graphically control a remote computer. Both are indispensable for modern business operations, and their compromise can lead to data breaches,
ransomware deployment, and severe operational disruptions.

Anatomy of the Campaign: Coordinated Attacks and Scale

The observed attacks were not isolated incidents but rather a coordinated effort from a network of Ukrainian-based autonomous systems. The sheer volume — hundreds of thousands of attacks – signifies a well-resourced and
organized operation. The duration, up to three days, suggests a methodical approach aimed at bypassing defenses and persistence. This scale places immense pressure on an organization’s detection and response capabilities,
making it difficult to distinguish legitimate login attempts from malicious activity without robust security measures in place.

Remediation Actions and Proactive Defense Strategies

Given the persistent nature of such attacks, organizations must adopt a proactive and layered defense strategy. Protecting SSL VPN and RDP systems requires a combination of technical controls, policy enforcement, and user education.

• Implement Multi-Factor Authentication (MFA): This is the single most effective defense against credential-based attacks. Even if an attacker obtains a password, MFA will prevent unauthorized access. Popular MFA solutions
  integrate seamlessly with both SSL VPN and RDP.
• Strong, Unique Passwords and Regular Rotation: Enforce policies requiring complex, unique passwords that are regularly changed. Utilize password managers to help users manage strong credentials.
• Account Lockout Policies: Configure aggressive account lockout thresholds for repeated failed login attempts. While password-spraying attempts to bypass this, it remains an essential defense against traditional brute-force.
• Geo-Blocking and IP Whitelisting: Restrict access to SSL VPN and RDP services from specific geographic regions if not required for business operations. For RDP, consider whitelisting only known, authorized IP addresses.
• Network Segmentation: Isolate critical RDP and VPN endpoints from other internal networks to limit lateral movement in case of a breach.
• Patch Management: Regularly update and patch all SSL VPN and RDP software to address known vulnerabilities. While this report doesn’t specify particular CVEs exploited, unpatched systems are always at higher risk. For instance,
  vulnerabilities like CVE-2019-1181 and CVE-2019-1182 (BlueKeep related)
  highlight the critical importance of keeping RDP secure.
• Monitoring and Alerting: Implement robust logging and monitoring for failed login attempts, unusual access patterns, and suspicious network activity on SSL VPN and RDP services. Integrate these logs with a SIEM (Security
  Information and Event Management) system for centralized analysis and alerting.
• Security Awareness Training: Educate employees about the risks of phishing, social engineering, and the importance of strong password hygiene.

Tools for Detection and Mitigation

Several tools can assist in detecting, preventing, and mitigating brute-force and password-spraying attacks on SSL VPN and RDP systems.

Conclusion

The reported campaigns from Ukrainian-based autonomous systems highlight the relentless and evolving nature of cyber threats. Attacks targeting remote access systems like SSL VPN and RDP are particularly dangerous due to their direct
path into an organization’s network. By implementing robust multi-factor authentication, strong password policies, vigilant monitoring, and timely patching, organizations can significantly enhance their resilience against these
sophisticated brute-force and password-spraying campaigns, protecting their critical assets and maintaining operational integrity.