Suspected state-sponsored hackers have exploited a zero-day vulnerability in Palo Alto Networks firewalls, identified as CVE-2024-3400, since March 26. These hackers have utilized the compromised devices to breach internal networks, pilfer data, and hijack credentials.

Palo Alto Networks issued a warning on the active exploitation of an unauthenticated remote code execution flaw in its PAN-OS firewall software. Patch updates are slated for release on April 14. Given the ongoing exploitation, Palo Alto Networks opted to disclose the vulnerability and provide interim mitigations for customers until patches are fully deployed.

Further insights into the zero-day exploitation emerged from a subsequent report by Volexity, the entity that discovered the flaw. According to Volexity, hackers have been exploiting the vulnerability since March, employing a custom backdoor dubbed 'Upstyle' to infiltrate target networks and execute data theft. The activity, tracked under the designation UTA0218, is strongly suspected to be orchestrated by state-sponsored threat actors.

Volexity's investigation traced the zero-day exploitation to April 10, primarily targeting the GlobalProtect feature of Palo Alto Networks PAN-OS. The subsequent deployment of identical exploitation methods at another customer site underscored the severity of the situation. Despite the exploitation period starting as early as March 26, payloads were not deployed until April 10.

The 'Upstyle' backdoor, facilitated by a Python script, enables remote command execution on compromised devices. The backdoor leverages a path configuration file to execute commands, allowing threat actors to operate stealthily within compromised environments.

In addition to the 'Upstyle' backdoor, Volexity observed the deployment of additional payloads, including reverse shells, PAN-OS configuration data exfiltration tools, and the Golang tunneling tool 'GOST.' In some instances, threat actors pivoted to internal networks to steal sensitive files, such as Active Directory databases and browser data from specific targets.

Volexity recommends two methods for detecting compromised Palo Alto Networks firewalls: generating Tech Support Files to analyze forensic artifacts and monitoring network activity for specific indicators of compromise.

This incident underscores the increasing targeting of network devices by threat actors, as demonstrated by previous campaigns exploiting vulnerabilities in Fortinet, SonicWall, Cisco, TP-Link, and Barracuda devices.