Dubbed "Fox Kitten," the cyber-espionage campaign is said to have been directed at companies from the IT, telecommunication, oil and gas, aviation, government, and security sectors.
"We estimate the campaign revealed in this report to be among Iran's most continuous and comprehensive campaigns revealed until now," ClearSky researchers said.
"The revealed campaign was used as a reconnaissance infrastructure; however, it can also be used as a platform for spreading and activating destructive malware such as ZeroCleare and Dustman."
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Tying the activities to threat groups APT33, APT34, and APT39, the offensive — conducted using a mix of open source and self-developed tools — also facilitated the groups to steal sensitive information and employ supply-chain attacks to target additional organizations, the researchers said.
Exploiting VPN Flaws to Compromise Enterprise Networks
The primary attack vector employed by the Iranian groups has been the exploitation of unpatched VPN vulnerabilities to penetrate and steal information from target companies. The prominent VPN systems exploited this way included Pulse Secure Connect (CVE-2019-11510), Palo Alto Networks' Global Protect (CVE-2019-1579), Fortinet FortiOS (CVE-2018-13379), and Citrix (CVE-2019-19781).
ClearSky noted that the hacking groups were able to successfully acquire access to the targets' core systems, drop additional malware, and laterally spread across the network by exploiting "1-day vulnerabilities in relatively short periods of time."
Upon successfully gaining an initial foothold, the compromised systems were found to communicate with attacker-control command-and-control (C2) servers to download a series of custom VBScript files that can, in turn, be used to plant backdoors.
Furthermore, the backdoor code in itself is downloaded in chunks so as to avoid detection by antivirus software installed on the infected computers. It's the job of a separate downloaded file — named "combine.bat" — to stitch together these individual files and create an executable.
To perform these tasks and achieve persistence, the threat actors exploited tools such as Juicy Potato and Invoke the Hash to gain high-level privileges and laterally move across the network. Some of the other tools developed by the attackers include:
- STSRCheck - A tool for mapping databases, servers, and open ports in the targeted network and brute-force them by logging with default credentials.
- Port.exe - A tool to scan predefined ports and servers.
Once the attackers gained lateral movement capabilities, the attackers move to the final stage: execute the backdoor to scan the compromised system for relevant information and exfiltrate the files back to the attacker by establishing a remote desktop connection (using a self-developed tool called POWSSHNET) or opening a socket-based connection to a hardcoded IP address.
In addition, the attackers used web shells in order to communicate with the servers located inside the target and upload files directly to a C2 server.
The Work of Multiple Iranian Hacking Groups
Based on the campaign's use of web shells and overlaps with the attack infrastructure, the ClearSky report highlighted that the attacks against VPN servers are possibly linked to three Iranian groups — APT33 ("Elfin"), APT34 ("OilRig") and APT39 (Chafer).
What's more, the researchers assessed that the campaign is a result of a "cooperation between the groups in infrastructure," citing similarities in the tools and work methods across the three groups.
Just last month, Iranian state-backed hackers — dubbed "Magnallium" — were discovered carrying out password-spraying attacks targeting US electric utilities as well as oil and gas firms.
Given that the attackers are weaponizing VPN flaws within 24 hours, it's imperative that organizations install security patches as and when they are available.
Aside from following the principle of least privilege, it also goes without saying that critical systems are monitored continuously and kept up to date. Implementing two-step authentication can go a long way towards minimizing unauthorized logins.