Pierluigi Paganini
April 24, 2024
Cisco Talos warned that the nation-state actor UAT4356 (aka STORM-1849) has been exploiting two zero-day vulnerabilities in Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) firewalls since November 2023 to breach government networks worldwide.
Cisco Talos researchers tracked this cyber-espionage campaign as ArcaneDoor.
Early in 2024, a customer contacted Cisco to report a suspicious related to its Cisco Adaptive Security Appliances (ASA). PSIRT and Talos launched an investigation to support the customer.
The experts discovered that the UAT4356 group deployed two backdoors, respectively called “Line Runner” and “Line Dancer.”
Cisco reported that the sophisticated attack chain employed by the attackers impacted a small set of customers. The experts have yet to identify the initial attack vector, however, they discovered the threat actors exploited two vulnerabilities ( (denial of service) and (persistent local code execution)) as zero-days in these attacks.
The Line Dancer in-memory implant that acts as a memory-resident shellcode interpreter that allows adversaries to execute arbitrary shellcode payloads. On compromised ASA devices, attackers utilize the host-scan-reply field to deliver shellcode, bypassing the need for CVE-2018-0101 exploitation. By redirecting the pointer to the Line Dancer interpreter, attackers can interact with the device through POST requests without authentication. Threat actors used Line Dancer to execute various commands, including disabling syslog, extracting configuration data, generating packet captures, and executing CLI commands. Additionally, Line Dancer hooks into the crash dump and AAA processes to evade forensic analysis and establish remote access VPN tunnels.
The Line Runner allows attackers to maintain persistence on compromised ASA devices. It exploits a legacy capability related to VPN client pre-loading, triggering at boot by searching for a specific file pattern on disk0:. Upon detection, it unzips and executes a Lua script, providing persistent HTTP-based backdoor access. This backdoor survives reboots and upgrades, allowing threat actors to maintain control. Additionally, the Line Runner was observed retrieving staged information facilitated by the Line Dancer component.
“ArcaneDoor is a campaign that is the latest example of state-sponsored actors targeting perimeter network devices from multiple vendors. Coveted by these actors, perimeter network devices are the perfect intrusion point for espionage-focused campaigns. As a critical path for data into and out of the network, these devices need to be routinely and promptly patched; using up-to-date hardware and software versions and configurations; and be closely monitored from a security perspective.” reads the published by Cisco, which also includes Indicators of Compromise (). “Gaining a foothold on these devices allows an actor to directly pivot into an organization, reroute or modify traffic and monitor network communications.”
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