As long as we've had the internet, users have tried to obfuscate how and what they are connecting to. In some cases, this is to work around restrictions put in place by governments or a desire to access content that is not otherwise available in a given region.
This is why technologies like VPNs and The Onion Router (TOR) become popular: They allow users to easily access content without exposing their IP address or location. These technologies are intended to protect users and information and have done a good job of doing so. However, adversaries have taken notice and are using proxy networks for malicious activities.
Proxy Chain Services
It is important to distinguish the different proxy chain services, as there are legitimate reasons for some of them to exist. From a privacy/defender point-of-view, they can be split into the following groups:
- VPN and TOR: These services provide the user anonymity, but the defender can, for the most part, determine that it's receiving requests from these networks. As such, there is no expectation that the origin of the connection is the exact same as the user’s physical location. The user has no control of the path or exit node location.
- Commercial residential services: These provide anonymity to users, while at the same time allowing them to choose the exit point. These services do not provide any clues to the defender about the nature of the connection.
- Malicious proxy services: Threat actors use these networks to hide their location and choose their exit node. These are set up to be used by malicious operators from multiple sources. They can take two shapes: The nodes are installed on leased servers from different providers in different regions, or their nodes can be compromised edge devices that bounce connections in chains.
The first group has a clear legitimate use case, and the second has been advertised as a means to measure marketing engagement. However, threat actors can also use them without the bandwidth owner understanding what is at risk. The third case is clear: The networks are built to be rented for distributed denial-of-service (DDoS) attacks or access to be sold so other actors can anonymize their activities.
History
Leveraging proxy networks for malicious purposes was something we first stumbled on with our research into Honeygain. This was one of the first times we saw technologies like proxyware being abused maliciously.
Proxyware is a type of technology that uses agents installed by users to act as proxies for other users. The users installing these agents are typically compensated for adding their node to the proxy network. Criminals stumbled upon this quickly and began to weaponize and monetize it, allowing them to benefit from the anonymity these technologies provide since it traces back to a random computer in a random location. At the time, the focus was purely criminal in nature, but state-sponsored groups have been leveraging TOR and VPNs for decades to launch their attacks, typically dropping out of a VPN near the target.
State-sponsored groups also realize that TOR and VPNs have limitations and could potentially expose their operations, so they needed something more opaque and less traceable. Enter VPNFilter.
VPNFilter was the first large-scale proxy network leveraged by state-sponsored actors, in this case Russia. This completely changed how proxy networks were operated and would set the tradecraft for state-sponsored proxy networks for the next several years. The most unique aspect of VPNFilter was the targeting: small office and home office (SOHO) routers.
The network was made up of SOHO routers that were being compromised with malicious firmware providing a variety of capabilities, including interception and proxy capabilities.
This was also a fairly significant botnet, consisting of some 500,000 devices that created a massive network from which to launch attacks without repercussions. Fortunately, we worked with affected vendors, and they resolved many of the issues that were being exploited, both vulnerability and otherwise.
This wasn't the last time we saw Russian-aligned actors leveraging these types of botnets. A few years later, Cyclops Blink was uncovered. Another Russian actor controlled a proxy network that again primarily consisted of consumer devices.
The targeting of consumer devices for this type of activity has become the focus of state-sponsored groups’ foray into this space. They also make excellent targets, since many users leave default configurations in place and rarely think to update their devices. Fortunately, post-VPNFilter, many vendors have switched to automatic updates, allowing for more frequent patching. This has resulted in state-sponsored groups widening their targeting.
Today, we see not just SOHO routers, but also NAS and a variety of IoT devices being targeted and added to these networks. This problem has just gotten worse in the past several years.
State of the Art
As recently as September, the FBI took down a botnet associated with Chinese hacking activities. This was just the latest in a spate of attacks originating from proxy networks. This activity has been largely associated with Volt Typhoon by the U.S. Government, with a broader attribution of China-linked activities in the recent FBI takedown.
Currently, there are several proxy-based networks, with a focus on SOHO devices (e.g., routers, NAS, etc.) and a variety of IoT components (e.g., security cameras) being compromised and added to a botnet that, in some ways, mirrors Mirai botnet activities.
The basic operating model for these botnets is that they are peer-to-peer, meaning there is no discernable routing. This model provides a sophisticated network of devices to obfuscate the true origin of an attack, and in many circumstances, allows the attacker to appear in close proximity to the victim, including coming from geographically adjacent residential networks.
The attacks originating from these networks have been tied to espionage and the targeting of critical infrastructure in the U.S. and globally. Most countries are concerned with this escalation, and it has the attention of the majority of vendors in this space.
These networks have also grown with staggering efficiency, with new nodes being added constantly as other nodes fall off and need to be compromised again. Based on reporting, the majority of these infections are using N-Day vulnerabilities or weak credentials to gain access, something we've seen repeatedly out of botnets like Mirai for the last decade. The major difference is that Mirai is used to conduct DDoS attacks, and the new iterations are being used to launch state-sponsored attacks with anonymity.
Network Resiliency Coalition
The repeated use of N-Day vulnerabilities and weak credentials ties into the work that Cisco has been doing for some time related to old and outdated networking equipment and the risks they introduce. The Network Resiliency Coalition is one of the projects aimed at trying to resolve this difficult problem. Anonymization networks' reliance on networking equipment, specifically exploiting known vulnerabilities, adds more weight to the importance of this effort. By working with industry peers, Cisco is trying to help remove many of the systems that are being abused in these attacks by working with vendors to ensure proper patching is provided to mitigate these known vulnerabilities, in a timely manner.
More projects like this that encompass the IoT industry and the non-edge SOHO appliances like NAS devices would also have a contribution to the fight against anonymization networks. This combined with better credential management, most notably ensuring that default credentials are complex and unique, could make a huge impact on how successful these networks are in continuing to grow. Vendors are working to try and resolve some of these weaknesses, but it also is paramount for defenders to take note.
Impact on Defenders
This continued focus by state-sponsored groups to leverage these networks presents problems for defenders. Attacks from these groups are likely to be coming from residential networks, potentially even from residential networks in the same cities and countries as your organization operates, making identification and attribution increasingly difficult.
Organizations need to realize that attacks can come from anywhere, even the same IP space that your employees connect to their VPNs, so plan accordingly.
This is further complicated by the increased focus by state-sponsored groups on the use of legitimate credentials. If you have a connection coming from the same IP space as your employees, using legitimate credentials organizations have little hope to stop it. This is where the increased focus on identity comes into play — organizations need to start taking additional steps to be able to distinguish between the illegitimate and legitimate use of credentials, and that ties back to behavior.
Increasingly, organizations should be looking at users’ behavior when it comes to connections.
- Are they using their typical device type? (e.g., Windows desktop/MacOS laptop)
- Are they logging on during their typical hours? (e.g., 9-5 M-F)
- Are there other managed devices in proximity?
- Are they using their managed device?
This last point is a critical one. For organizations particularly concerned with credential abuse, managed device access restriction may be the best option.
This ensures that only managed devices can connect to corporate VPNs through technologies like certificates.
The downside to this approach is that it's expensive, and for many organizations not practical, but for those with the budgets and the concern, it's a needed escalation beyond just multi-factor authentication (MFA).
You may have noticed we haven’t mentioned MFA until now. But that’s because in 2024, it's assumed you've already rolled out MFA for medium to large enterprises. It is no longer an optional security feature.
Defenders need to adjust for the state-sponsored threats they will be facing in 2024 and beyond. This means adding more identity capabilities in the near term and looking at additional security protections like managed device-only access in the future.