Your Asus router may be compromised – here's how to tell and what to do

Do you own an Asus router? If so, your device may have been one of thousands compromised in a large campaign waged by cybercriminals looking to exploit it. In a blog post published Wednesday, security firm GreyNoise revealed that the attack was staged by what it suggests is “a well-resourced and highly capable adversary.”

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To gain initial access, the attackers used brute-force login techniques and two different methods to bypass the built-in authentication. They’ve also been able to exploit certain vulnerabilities not yet assigned official CVE numbers. Once they’d accessed the router, they were able to run arbitrary system commands by exploiting a known security flaw identified as CVE-2023-39780.

Though no malware was actually installed, the attackers certainly left their mark.

More than 9,000 Asus routers affected

By using built-in Asus settings, they were able to set up SSH access, a secure way to connect to and control a remote device. They also installed a backdoor to return easily to the router’s firmware without worrying about authentication. The backdoor was stored in non-volatile memory (NVRAM), which meant it couldn’t be removed by rebooting the router or updating its firmware. To avoid being caught, the criminals even disabled logging, which would otherwise record their access.

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Based on data from internet scanner Censys, more than 9,000 Asus routers are affected, and that number is growing. However, GreyNoise said that over the past three months, it witnessed only 30 related requests to access the affected routers. That seems to be a sign that the campaign is moving along slowly and quietly.

If no malware is installed, what’s the goal behind the attack?

“This appears to be part of a stealth operation to assemble a distributed network of backdoor devices — potentially laying the groundwork for a future botnet,” GreyNoise said in its post.

And who’s behind it?

“The tactics used in this campaign — stealthy initial access, use of built-in system features for persistence, and careful avoidance of detection — are consistent with those seen in advanced, long-term operations, including activity associated with advanced persistent threat (APT) actors and operational relay box (ORB) networks. While GreyNoise has made no attribution, the level of tradecraft suggests a well-resourced and highly capable adversary.”

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The language used by GreyNoise, particularly the reference to APTs, suggests a nation-state or attackers working on behalf of a hostile government. Though GreyNoise didn’t cite any particular adversary, such attacks have been attributed to different countries, including China, Russia, North Korea, and Iran.

Using its AI-powered payload analysis tool Sift and its observation grid, GreyNoise discovered the attack on March 18. But the firm said it waited until now to disclose it publicly so it could have time to consult with its government and industry partners.

What should you do if you own an Asus router?

To see if your device has been compromised, log in to the router’s firmware. Look for the “Enable SSH” option under the Service or Administration settings. If your router was caught in the campaign, the settings will show that someone can log in to it using SSH over port 53282 with a truncated SSH public key of: ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAo41nBoVFfj4HlVMGV+YPsxMDrMlbdDZ…

Normally, updating the firmware would solve the problem, especially since Asus fixed the CVE-2023-39780 flaw with its latest firmware update. If your router hasn’t been infected, be sure to update the firmware ASAP. But if your router has already been compromised, the backdoor remains even after an update.

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In that case, Asus advises you to remove or disable the SSH entry. You’ll also want to block the following four IP addresses: 101.99.91.151, 101.99.94.173, 79.141.163.179, and 111.90.146.237. Finally, you may want to factory reset your router and manually reconfigure it to make sure no traces of the backdoor remain.

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