The Rise of the Dragon

Wed 17 May 2023

Adam Cassar

Co-Founder

5 min read

Camaro Dragon, a Chinese state-sponsored group, has developed a custom firmware implant for TP-Link routers. Once installed, it can turn compromised routers into residential proxies. That weakens traditional cyber-defences, including GeoIP blocking, because traffic can appear to come from ordinary local connections. This article looks at how the malware works, why residential proxies matter for enterprise security, and where GeoIP security measures fall short.

Understanding the New Malware

Check Point's research describes Camaro Dragon's sophisticated attacks on European foreign affairs entities. The group uses a custom firmware implant, known as 'Horse Shell', designed specifically for TP-Link routers. The malware includes a backdoor that grants the attackers continuous access to compromised networks and allows them to build anonymous infrastructure.

'Horse Shell' can execute arbitrary commands on the infected router, transfer files, and relay communications using SOCKS tunnelling. Its design can be adapted to different vendors' firmware, suggesting the possibility of a wider spread.

The People and Intentions Behind The Malware

Investigations into the origin of the 'Horse Shell' malware by Check Point Research, Avast, and ESET point to a well-known cyber threat actor: Mustang Panda. This advanced persistent threat (APT) group, linked to the Chinese government, is known for complex attacks that often exploit Internet-facing network devices.

The primary function of 'Horse Shell' is to relay traffic between an infected device and the attackers' command and control servers. This method obscures the true source and destination of the communication, making it difficult to trace back to the attackers.

Importantly, Mustang Panda appears to choose router implant targets indiscriminately. The infection of a home router doesn't imply that the homeowner is a direct target. Instead, each infected router becomes a node in a broader chain that connects main infections with command and control operations.

Researchers identified this approach when they found the 'Horse Shell' implant during an investigation of targeted attacks against European foreign affairs entities. The implant allows the attackers to maintain ongoing access, establish anonymous infrastructure, and move laterally within compromised networks.

The Implications of Residential Proxies

Residential proxies serve as intermediaries, using real IP addresses issued by Internet Service Providers (ISPs). They are used across a range of applications, including business web scraping and anonymising user online activity.

Residential proxies become more serious when malware such as 'Horse Shell' is involved. This malware infects routers, turning them into a network of residential proxies that can then be used for malicious activity, including data breaches and distributed denial-of-service (DDoS) attacks.

Most importantly, this use of residential IP space can make an attack look as if it originates from a domestic source within the target's location. That undermines traditional cyber-defences.

GeoIP Security Measures and Their Limitations

GeoIP blocking, a traditional cyber security tool, works by limiting access from specific geographical regions or networks frequently associated with cyber threats. However, this method is becoming less effective against the rising use of residential proxies.

Residential proxies can disguise the actual origin of a cyber attack, giving the illusion that it's originating from a trusted, usually local, location. This capability allows them to effectively bypass GeoIP blocking measures. Consequently, malicious actors using residential proxies can carry out their activities with less obvious attribution and often go undetected.

The key operational issue is the exploitation of home routers by malware like 'Horse Shell,' which turns these devices into unwitting participants in cyber attacks. This manipulation means an attack could appear to originate from a seemingly trusted domestic source, which can render GeoIP blocking ineffective.

This threat shows why cyber security needs a more layered approach. Sole reliance on GeoIP blocking is no longer enough. As malware evolves to exploit residential proxies, detection and defence strategies need to adapt. Specifically, it's important to recognise that relying solely on GeoIP blocking, or trusting apparently local connections and deny-listing countries like Russia and China, can create a false sense of security.

Detecting Residential Proxies: The Role of Network Fingerprinting

The rise of residential proxy malware makes network fingerprinting important for identifying these threats. Five techniques can help detect residential proxies:

1. TCP Fingerprinting: Proxied requests may generate TCP fingerprints that don't match the expected device type. For example, a request from a residential IP address that bears the fingerprint of a server OS could be a strong signal of a proxy.

2. TLS and HTTP/2 Signatures: As with TCP fingerprints, unusual TLS and HTTP/2 signatures could reveal proxies. An incoming request using a version of TLS or HTTP/2 not commonly used in residential networks might indicate a proxy.

3. JavaScript-based Fingerprinting: This method identifies the specific browser in use. Discrepancies in JavaScript fingerprints, or the absence of a fingerprint, could suggest the presence of a residential proxy.

4. Timing Analysis: The timing of requests can also be a signal. Proxied requests might exhibit longer or inconsistent intervals between requests, indicating a residential proxy.

5. Port Scanning: This technique can detect open ports that could indicate the presence of SOCKS or other proxies, revealing possible exposure to threats.

While residential proxies have legitimate uses, such as web scraping, those applications sit beside a more serious risk: compromised trusted or local networks can be turned into proxy infrastructure at scale. Cyber threats like 'Horse Shell' use residential proxies to undermine traditional GeoIP security measures, which means defence strategies need to keep evolving.

In Part 1 of our series on residential proxies, we provide an overview of this topic and why it matters to security teams. From basic uses to their role in complicated cyber attacks, we cover the key points.

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