Researchers this month uncovered a two-year-old Linux-based remote access trojan dubbed AVrecon that enslaves Internet routers into botnet that bilks online advertisers and performs password-spraying attacks. Now new findings reveal that AVrecon is the malware engine behind a 12-year-old service called SocksEscort, which rents hacked residential and small business devices to cybercriminals looking to hide their true location online.

Image: Lumen’s Black Lotus Labs.

In a report released July 12, researchers at Lumen’s Black Lotus Labs called the AVrecon botnet “one of the largest botnets targeting small-office/home-office (SOHO) routers seen in recent history,” and a crime machine that has largely evaded public attention since first being spotted in mid-2021.

“The malware has been used to create residential proxy services to shroud malicious activity such as password spraying, web-traffic proxying and ad fraud,” the Lumen researchers wrote.

Malware-based anonymity networks are a major source of unwanted and malicious web traffic directed at online retailers, Internet service providers (ISPs), social networks, email providers and financial institutions. And a great many of these “proxy” networks are marketed primarily to cybercriminals seeking to anonymize their traffic by routing it through an infected PC, router or mobile device.

Proxy services can be used in a legitimate manner for several business purposes — such as price comparisons or sales intelligence — but they are massively abused for hiding cybercrime activity because they make it difficult to trace malicious traffic to its original source. Proxy services also let users appear to be getting online from nearly anywhere in the world, which is useful if you’re a cybercriminal who is trying to impersonate someone from a specific place.

Spur.us, a startup that tracks proxy services, told KrebsOnSecurity that the Internet addresses Lumen tagged as the AVrecon botnet’s “Command and Control” (C2) servers all tie back to a long-running proxy service called SocksEscort.

SocksEscort[.]com, is what’s known as a “SOCKS Proxy” service. The SOCKS (or SOCKS5) protocol allows Internet users to channel their Web traffic through a proxy server, which then passes the information on to the intended destination. From a website’s perspective, the traffic of the proxy network customer appears to originate from a rented/malware-infected PC tied to a residential ISP customer, not from the proxy service customer.

The SocksEscort home page says its services are perfect for people involved in automated online activity that often results in IP addresses getting blocked or banned, such as Craigslist and dating scams, search engine results manipulation, and online surveys.

Spur tracks SocksEscort as a malware-based proxy offering, which means the machines doing the proxying of traffic for SocksEscort customers have been infected with malicious software that turns them into a traffic relay. Usually, these users have no idea their systems are compromised.

Spur says the SocksEscort proxy service requires customers to install a Windows based application in order to access a pool of more than 10,000 hacked devices worldwide.

“We created a fingerprint to identify the call-back infrastructure for SocksEscort proxies,” Spur co-founder Riley Kilmer said. “Looking at network telemetry, we were able to confirm that we saw victims talking back to it on various ports.”

According to Kilmer, AVrecon is the malware that gives SocksEscort its proxies.

“When Lumen released their report and IOCs [indicators of compromise], we queried our system for which proxy service call-back infrastructure overlapped with their IOCs,” Kilmer continued. “The second stage C2s they identified were the same as the IPs we labeled for SocksEscort.”

Lumen’s research team said the purpose of AVrecon appears to be stealing bandwidth – without impacting end-users – in order to create a residential proxy service to help launder malicious activity and avoid attracting the same level of attention from Tor-hidden services or commercially available VPN services.

“This class of cybercrime activity threat may evade detection because it is less likely than a crypto-miner to be noticed by the owner, and it is unlikely to warrant the volume of abuse complaints that internet-wide brute-forcing and DDoS-based botnets typically draw,” Lumen’s Black Lotus researchers wrote.

Preserving bandwidth for both customers and victims was a primary concern for SocksEscort in July 2022, when 911S5 — at the time the world’s largest known malware proxy network — got hacked and imploded just days after being exposed in a story here. Kilmer said after 911’s demise, SocksEscort closed its registration for several months to prevent an influx of new users from swamping the service.

Danny Adamitis, principal information security researcher at Lumen and co-author of the report on AVrecon, confirmed Kilmer’s findings, saying the C2 data matched up with what Spur was seeing for SocksEscort dating back to September 2022.

Adamitis said that on July 13 — the day after Lumen published research on AVrecon and started blocking any traffic to the malware’s control servers — the people responsible for maintaining the botnet reacted quickly to transition infected systems over to a new command and control infrastructure.

“They were clearly reacting and trying to maintain control over components of the botnet,” Adamitis said. “Probably, they wanted to keep that revenue stream going.”

Frustratingly, Lumen was not able to determine how the SOHO devices were being infected with AVrecon. Some possible avenues of infection include exploiting weak or default administrative credentials on routers, and outdated, insecure firmware that has known, exploitable security vulnerabilities.
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