Various Botnets Pummel Year-Old TP-Link Flaw in IoT Attacks

A number of botnets are pummeling a nearly year-old command-injection vulnerability in TP-Link routers to compromise the devices for IoT-driven distributed denial of service (DDoS) attacks.

There already is a patch for the flaw, tracked as CVE-2023-1389, found in the Web management interface of the TP-Link Archer AX21 (AX1800) Wi-Fi router and affecting devices Version 1.1.4 Build 20230219 or prior.

However, threat actors are taking advantage of unpatched devices to dispatch various botnets — include Moobot, Miori, AGoent, a Gafgyt variant, and variants of the infamous Mirai botnet — that can compromise the devices for DDoS and further nefarious activity, according to a blog post from Fortiguard Labs Threat Research.

"Recently, we observed multiple attacks focusing on this year-old vulnerability," which already was previously exploited by the in Mirai botnet, according to the post by Fortiguard researchers Cara Lin and Vincent Li. Fortiguard's IPS telemetry has detected significant traffic peaks, which alerted the researchers to the malicious activity, they said.

Exploiting the TP-Link Flaw

The flaw creates a scenario in which there is no sanitization of the "Country" field of the router's management interface, "so an attacker can exploit it for malicious activities and gain foothold," according to TP-Link's security advisory for the flaw.

"This is an unauthenticated command-injection vulnerability in the 'locale' API available via the web management interface," Lin and Li explained.

To exploit it, users can query the specified form "country" and conduct a "write" operation, which is handled by the "set_country" function, the researchers explained. That function calls the "merge_config_by_country" function and concatenates the argument of the specified form "country" into a command string. This string is then executed by the "popen" function.

"Since the 'country' field won't be emptied, the attacker can achieve command injection," the researchers wrote.

Botnets to the Siege

TP-Link's advisory when the flaw was revealed last year included acknowledgement of exploitation by the Mirai botnet. But since then other botnets as well as various Mirai variants also have taken siege against vulnerable devices.

One is Agoent, a Golang-based agent bot that attacks by first fetching the script file "exec.sh" from an attacker-controlled website, which then retrieves the Executable and Linkable Format (ELF) files of different Linux-based architectures.

The bot then executes two primary behaviors: the first is to create the host username and password using random characters, and the second is to establish connection with command and control (C2) to pass on the credentials just created by the malware for device takeover, the researchers said.

A botnet that creates denial of service (DoS) in Linux architectures called the Gafgyt variant also is attacking the TP-Link flaw by downloading and executing a script file and then retrieving Linux architecture execution files with the prefix filename "rebirth." The botnet then gets the compromised target IP and architecture information, which it concatenates into a string that is part of its initial connection message, the researchers explained.

"After establishing a connection with its C2 server, the malware receives a continuous 'PING' command from the server to ensure persistence on the compromised target," the researchers wrote. It then waits for various C2 commands to create DoS attacks.

The botnet called Moobot also is attacking the flaw to conduct DDoS attacks on remote IPs via a command from the attacker's C2 server, the researchers said. While the botnet targets various IoT hardware architectures, Fortiguard researchers analyzed the botnet's execution file designed for the "x86_64" architecture to determine its exploitation activity, they said.

A variant of Mirai also is conducting DDoS attacks in its exploitation of the flaw by sending a packet from the C&C server to direct the endpoint to initiate the attack, the researchers noted.

"The command specified is 0x01 for a Valve Source Engine (VSE) flood, with a duration of 60 seconds (0x3C), targeting a randomly selected victim's IP address and the port number 30129," they explained.

Miori, another Mirai variant, also has joined the fray to conduct brute-force attacks on compromised devices, the researchers noted. And they also observed attacks by Condi that remains consistent with a version of the botnet that was active last year.

The attack retains the function to prevent reboots by deleting binaries responsible for shutting down or rebooting the system, and scans active processes and cross-references with predefined strings to terminate processes with matching names, the researchers said.

Patch & Protect to Avoid DDoS

Botnet attacks that exploit device flaws to target IoT environments are "relentless," and thus users should be vigilant against DDoS botnets," the researchers noted. Indeed, IoT adversaries are advancing their attacks by pouncing on unpatched device flaws to further their sophisticated attack agendas.

Attacks against TP-Link devices can be mitigated by applying the available patch for affected devices, and this practice should be followed for any other IoT devices "to safeguard their network environments from infection, preventing them from becoming bots for malicious threat actors," the researchers wrote.

Fortiguard also included in its post various indicators of compromise (IoCs) for the different botnet attacks, including C2 servers, URLs, and files that can help server administrators identify an attack.