What is an Advanced Persistent Threat (APT)?

An APT attack is always carefully researched and planned. Attackers must infiltrate networks and implant agents without detection. Data collection must also evade security measures for the duration of the attack.

Because of these technical requirements, well-resourced and highly skilled cybercriminal groups tend to execute Advanced Persistent Threat attacks. They present a significant cybersecurity risk for enterprises, and can lead to:

• Site hijacking and loss of control over business assets
• Data breaches and privacy violations
• Theft of intellectual property and sale to competitors
• Damage to databases and other critical assets.

Stages of an APT attack

Advanced Persistent Threat attacks are complex and strategically planned. They are rarely speculative ventures and do not rely on chance to gain access to a targeted network.

Stages of an APT attack generally include:

1. Infiltrating the network

APT attacks begin with network infiltration. Attackers must breach firewalls and threat detection systems before they can deliver malware payloads.

Most attacks infiltrate target networks via phishing or social engineering techniques. APT attackers research network users and create content related to their professional or personal lives. Well-engineered content prompts recipients to click malicious links or download infected attachments.

In some cases, attackers choose high-value targets. Known as "whaling", this social engineering method often enables wider network access. Greater access allows attackers to position their agents strategically to evade detection and gather data.

Other examples use SQL injection techniques to compromise web forms. Insiders could also deliver APTs via physical devices. There are many ways to start an attack, and companies need to take each method into account.

2. Delivering APT payloads

The second stage initiates data collection and monitoring. Attackers move laterally within the network, seeking data storage containers and places to collect high-value traffic.

Attackers also collect credentials where possible. Typically, infiltrators seek to raise the company hierarchy, adding privileges with each new compromise. Collecting credentials enables attackers to pass authentication systems and access sensitive data across the network.

At this stage, APT attackers commonly engineer backdoors. Backdoors allow attackers to restore their agents following detection, extending the lifespan of an APT attack.

3. Data extraction

When the groundwork is complete, APT attackers begin collecting and exfiltrating data.

During this stage, attackers adopt living-off-the-land tactics, hijacking legitimate tools like PowerShell to gather information. Attackers may employ polymorphic malware that changes its composition to evade detection. They may also hide agents within videos, documents, or images via steganography techniques.

Once concealed, data flows from the Advanced Persistent Threat to secure external locations. Victims have no access to data once it leaves the network, and attackers are free to use it as they wish.

Internal security teams may detect data extraction and initiate countermeasures. However, APT attackers can counter defenses via denial-of-service attacks. DDoS attacks consume system resources and create "white noise" to distract security professionals.

Sometimes, data extraction is not the main goal. Attackers may delete critical data to damage the target business or control network infrastructure to disrupt operations.

Common APT attack methods

There are many APT techniques. If attackers fail with one method, they will probably try another. As a result, security policies must include measures to guard against each attack vector.

• Spear phishing. Spear phishing uses targeted emails to persuade victims to click links or download attachments. Fake websites can deliver malware or obtain credentials via deceptive online forms. Attachments directly deliver payloads to devices on the targeted network.
• Whaling. Whaling uses carefully researched emails, phone calls, or in-person meetings to target executives. Whalers seek credentials for administrative accounts, allowing them to roam freely across the network.
• Supply chain attacks. Criminals use third-party network access to deliver Advanced Persistent Threats. Companies may secure employee accounts and devices but fail to monitor access by partners.
• Credential attacks. Attackers use databases of known credentials to guess user passwords (also known as credential stuffing). This technique often works if employees routinely re-use passwords on different services.
• Watering hole attacks. In these attacks, criminals target websites used by a company's employees. For example, attackers could compromise a professional technical support forum. Criminals can directly steal credentials or create identical fake watering holes to gather information.
• Exploits. Exploits target flaws in applications or operating systems that face the public internet. Left unpatched, out-of-date software enables network access, providing APT attackers with a base to launch operations.

What are the signs of an APT attack?

Security teams must know what to look for when identifying Advanced Persistent Threats. Characteristics of APT attacks include:

• Suspicious user behavior. Attackers may hijack legitimate user accounts but act in ways normal users would not. For example, attackers may log on at erratic times of night or connect from different locations.
• Spikes in Trojan detections. Trojan malware spikes often characterize APT incidents as attackers often use Trojans to engineer the backdoors needed to sustain their campaigns.
• Data bundling. Attackers may prepare data on the target network for convenient exfiltration. Security teams should check for unusual data bundling and seek a business justification for these changes.
• Unexpected traffic increases. Network traffic flows are usually predictable, with reasons for increased data flows. Unexplained sudden increases should trigger alerts and can signify Advanced Persistent Threat attacks.
• Epidemics of phishing reports. Security teams should also monitor phishing incidents. Users flagging many business emails as suspicious could indicate an organized APT campaign.

Advanced Persistent Threat examples

There have been many recent examples of Advanced Persistent Threats. Each group has a unique signature and end goal. Some seek sensitive data or intellectual property for sale. Others are political disruptors.

Here are a few notorious case studies.

• Wicked Panda. Emerging from China in the 2010s, Wicked Panda (or APT41) uses SQL injection to infect targets. When the exploit is secured, attackers deliver a fragmented Cobalt Strike Beacon which reassembles and starts collecting data. The split beacon design makes Wicked Panda attacks hard to detect despite its age.
• Helix Kitten. Thought to be Iranian, Helix Kitten (APT34) relies on PowerShell exploits and app backdoors, but the main entry points are spear phishing and infected Microsoft Excel macros. Focused on Middle Eastern and international organizations, this APT carries out espionage for private and government clients.
• Ocean Buffalo. Vietnamese APT Ocean Buffalo (APT32) has been active since 2012. This Advanced Persistent Threat has attacked Chinese and Western targets, mixing state espionage and financial motives. Unlike other APTs listed here, Ocean Buffalo has spread via fake apps on Android marketplaces.
• GhostNet. First identified in 2009, GhostNet started by targeting Tibetan organizations and combined raw data collection with audio and video capture—taking APTs to a new level. After 2009, targets widened to include over 100 embassies before the APT declined. Unfortunately, over the past 10 years, the techniques pioneered by GhostNet have rapidly evolved.

How to protect against APT attacks

APTs can harvest your financials, customer records, intellectual property, and even video conversations between employees or clients.

Blocking and removing APTs is a cybersecurity priority for all organizations. Fortunately, security teams can cut persistent threat risks by hardening their perimeter defenses and scanning for threats. Here are some ways to do so:

Protect attack surfaces

Advanced threat protection starts by securing your attack surfaces.

Strong password security is essential. Attackers should not be able to access network resources without legitimate credentials. Users should change passwords regularly, only use strong passwords, and never re-use passwords for different logins.

Multi-factor authentication adds greater security at the network edge. MFA requests more than two credentials for every login, including unique information or one-time codes. Even if attackers possess legitimate passwords and IDs, access is impossible.

Robust firewall protection blocks suspicious access requests and allows authorized traffic. Next-generation firewalls go further by scanning traffic for known malware—including many payloads linked to APTs.

Security teams should enforce strict device posture checks and allow only approved devices to use network resources. This includes mobile devices and remote-access laptops.

Implement patch management policies

Many APTs use exploits or injection techniques to access networks. Reduce the risk of these attack vectors by regularly updating firmware and internet-facing applications. Apply recommended OS and web application updates as soon as they are available.

Monitor network threats

Alongside securing the network edge, organizations must monitor traffic and detect potential APTs. Advanced Persistent Threats remain in the background for long periods and are hard to detect. However, you can detect the early stages of data extraction before situations become critical.

Internal network firewalls and threat management tools track data flows and access requests. They monitor and log the data users access. Use the data from monitoring tools to detect unusual behavior patterns and flag areas to investigate.

In particular, set up automated alerts to flag large data transfers or bulk re-classification of files. Honeypots inside the network may also help by attracting malicious actors.

Implement role-based access controls

An Advanced Persistent Threat can only succeed by escalating access privileges. Privilege escalation is easy if many users possess administrative privileges but hard if targets apply Zero Trust principles and minimize privileges assigned to individual users.

Assign permissions based on business roles and implement temporary escalations when needed. Audit orphaned accounts to remove obsolete users—a common source of illicit network entry.

Encrypt sensitive data

Cybercriminals may back down from APT attacks if strong encryption protects data on their targeted network. Always encrypt confidential data and store it in safe zones, separate from low-value network assets. Additionally, encrypt remote connections to avoid man-in-the-middle attacks.

Train staff to identify phishing attacks

Finally, remember that many APT infections result from social engineering techniques. Educate staff to identify suspicious links, attachments, and contacts. Create reporting systems to inform security teams about phishing patterns and reinforce staff training regularly to maintain awareness.