Security researchers have detected massive scanning campaigns targeting Cisco Adaptive Security Appliance (ASA) devices, with attackers probing over 25,000 unique IP addresses in coordinated waves that may signal an upcoming vulnerability disclosure.
GreyNoise cybersecurity researchers observed two significant scanning surges against Cisco ASA devices in late August.
The first wave involved more than 25,000 unique IP addresses scanning vulnerable devices in a single coordinated burst. A second, smaller but related campaign followed days later.
These attacks represent a dramatic increase from normal baseline activity, which typically registers fewer than 500 IP addresses per day.
Both campaigns specifically targeted the ASA web login path at /+CSCOE+/logon.html, a common reconnaissance marker used by attackers to identify exposed devices.
Coordinated Botnet Campaign
Analysis reveals that the August 26 wave was primarily driven by a single botnet cluster concentrated in Brazil.
Researchers isolated a specific client fingerprint and determined that roughly 14,000 of the 17,000 active IP addresses that day—more than 80 percent—were tied to this coordinated botnet operation.
The attackers used shared client signatures and spoofed Chrome-like user-agents, indicating a common scanning toolkit deployed across both events.
Subsets of the same IP addresses also probed Cisco Telnet/SSH services, signaling a focused campaign specifically targeting Cisco infrastructure rather than opportunistic scanning.
Global Attack Pattern
Over the past 90 days, scanning activity has shown distinct geographic patterns. Brazil emerged as the dominant source country, accounting for 64 percent of malicious traffic, followed by Argentina and the United States at 8 percent each.
Target countries tell a different story, with the United States bearing the brunt of attacks at 97 percent, while the United Kingdom and Germany faced 5 percent and 3 percent ,respectively.
This concentration suggests attackers are specifically hunting for vulnerable Cisco ASA devices in American networks.
The massive scanning campaigns may serve as an early warning signal for upcoming vulnerability disclosures.
GreyNoise research shows that scanning spikes often precede the announcement of new CVEs. Previous activity against Cisco ASA devices has surged shortly before new vulnerability disclosures, making these August events potentially significant indicators.
Cisco ASA devices have been prime targets for sophisticated threat actors. The ArcaneDoor espionage campaign used two zero-day vulnerabilities to infiltrate government networks.
Ransomware groups including Akira and LockBit have historically targeted these systems for initial network access.
Security teams should limit exposure by avoiding direct internet placement of ASA web portals, Telnet, or SSH services.
Organizations should implement multi-factor authentication for remote access and prepare for rapid patching if new vulnerabilities emerge.
Even fully patched organizations should consider blocking the identified malicious IP addresses to reduce the likelihood of appearing on target lists used for future exploit campaigns.
Continuous monitoring of scanning activity can provide early warning of emerging threats against critical network infrastructure.
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