What Are Zero Click Attacks and How Can You Protect Against Them?

What are Zero Click attacks, and how can you protect against them?

During a cyberattack, adversaries need to employ some method to successfully gain initial access to the victim's system. Once access is gained, attackers can carry out the latter stages of their attack to achieve their ultimate objectives.  The most common technique used in first stage attacks is phishing where users are baited into directly executing a malware on behalf of the attacker or sharing sensitive information such as login credentials.

However, some first stage attack techniques don't require the victim to trick the victim into clicking a file to execute malware. Collectively, these types of attacks are known as "Zero Click" attacks. 

In this article, our ethical hackers describe some techniques used in Zero Click attacks and why it is so hard to defend against them. Let's dive right in:

What Are Zero Click Attacks?

Zero Click attacks encompass a broad range of cyber techniques that do not require user interaction to execute malware to trigger the attacker's payload. Instead, Zero Click attacks take advantage of technical weaknesses in the victim's computer such as the OS, applications, or use other means to execute malicious code. 

Here are some examples of Zero Click attack techniques leveraged by attackers:

• Exploiting Known Or Zero Day Vulnerabilities: Exploiting vulnerabilities in software or hardware can allow attackers to breach public facing systems or move laterally once they have control of a system on the victim's network. Many vulnerabilities do not require any interaction from the user. For example, a zero-click exploit could allow an attacker to take control of the victim's device simply by sending a specially crafted message or image.  Or, compromising a weakness in a website could allow an attacker to upload a malicious file to a web server could place a web shell, allowing the victim to further execute arbitrary code at will

• Leveraging Attack Automation: Automated vulnerability scanners, automated attack scripts, or botnets could be used to identify and exploit vulnerable systems en masse, initiating zero-click attacks without manual intervention. Also, attackers can inject malicious code into files or data streams that are automatically processed by software or devices

• Supply Chain Attacks: Supply chain attacks target vulnerabilities in third-party software or services used by the victim, rather than directly targeting the victim's systems. By compromising a trusted vendor or service provider, attackers can distribute malicious updates or components that automatically execute on the victim's systems without any user interaction

• Password Brute-Force and Spraying Attacks: Attackers can brute-force passwords by repeatedly guessing until they successfully guess the correct password, or use data collected from phishing attacks, the dark web, or stolen in previous breaches in an attacks known as password spraying or credential stuffing in an attempt to gain unauthorized access to an account

• Man in the Middle (MitM) Attacks: Wireless and wired network sniffing attacks can reveal sensitive information such as passwords, and also allow an attacker to modify the data in transit to execute attacks against the victim's system

Why Are Zero Click Attacks So Hard To Defend Against?

Overall, several factors make zero-click attacks particularly challenging for defenders to detect, prevent, and mitigate effectively.

Here are some factors that make defending against Zero Click attacks so difficult:

• They Don't Require User Interaction: Traditional cyberattacks often rely on social engineering tactics to trick users into taking specific actions, such as clicking on malicious links or downloading infected files. Since there is no user interaction, defenders may struggle to identify the source of the attack. Zero Click attacks may also be harder to detect and mitigate since there are often no warning signs for users to recognize

• Automated Execution: Zero Click attacks can be automated, allowing attackers to exploit vulnerabilities at scale. This enables attackers to rapidly deploy and propagate their attacks across a wide range of targets. Automation can make it challenging for defenders to keep pace with the speed and volume of attacks

• Exploitation of Zero-Day Vulnerabilities: Zero Click attacks can target zero-day vulnerabilities, which are previously unknown and unpatched security flaws in software or hardware. Since there are no available patches or mitigations for zero-day vulnerabilities, defenders have limited options for defending against zero-click attacks that exploit these vulnerabilities, leaving them vulnerable until a patch is developed and deployed

How to Defend Against Zero Click Attacks?

Defending against zero-click attacks requires a combination of proactive and reactive measures and a robust strategy requires various types of internal controls such as preventive, detective, compensating, and corrective measures. Defensive measures should seek to reduce attack surface giving attackers less opportunity to exploit weaknesses, include defense in depth strategy to ensure a single breach can be contained, allow detection and recovery from a breach quickly and completely.

Here are several defenses that organizations can implement to mitigate the risks posed by zero-click attacks:

• Vulnerability management (proactive and preventative): 

  • Vulnerability scanning and remediation: By scanning all internal network and public facing infrastructure for known vulnerabilities defenders can seek to prevent attackers from exploiting them in the first place. This requires using vulnerability scanning software and ensuring that it is regularly updated with tests to find the most recently disclosed vulnerabilities and weak configurations. Any discovered vulnerabilities should be prioritized by risk and remediated as soon as possible

  • Patch management: Without leveraging a vulnerability scanner, users can increase their security by regularly applying security patches to software, firmware, and operating systems. This helps mitigate the risk of vulnerabilities that could be exploited in zero-click attacks and minimizes exposure to exploitable weaknesses

  • Threat intelligence sharing: Cyber threat intelligence (CTI) sharing exchange actionable threat intelligence with peer organizations and security communities. Leveraging CTI feeds helps identify new emerging threats, and supports prioritization of remediation efforts by providing some context to which known vulnerabilities are being actively exploited. One example is CISA's known exploited vulnerabilities (KEV) catalog which alerts organization's to activity in the global threat environment

• Virtualization (proactive and preventative): Employing virtualization technologies, such as deploying virtual machines (VMs), sandboxed virtual environments, Virtual Desktop Infrastructure (VDI), virtual private servers (VPS), and remote browser isolation (RBI) can provide a more secure temporary environment to execute applications, services, and files from the underlying host system. By running virtual environments, organizations can minimize the impact of zero-click attacks. If malware compromises one application or service the virtualization environment can be discarded periodically to prevent malware dwell time and  reduce the risk of lateral movement and data exfiltration.

• Endpoint protection (reactive and detective): Deploy endpoint protection solutions, such as antivirus software, endpoint detection and response (EDR) tools, and application whitelisting, to defend against malware and malicious code execution on endpoints. Leverage behavior-based detection techniques to identify anomalous activity indicative of zero-click attacks. Employ behavioral analytics and machine learning algorithms to analyze user and system behavior for indicators of compromise (IOCs) associated with zero-click attacks.

• Content filtering (proactive and detective): Utilize email filtering solutions to detect and block spam and more targeted phishing emails containing phishing links, or malicious content. Also, file format validation can be used to verify that a file's format strictly follows the expected format for a given file type, defenders can prevent some zero day attacks that cannot be identified with a malware scanning product. 

• Defense In Depth technical controls (proactive and compensating): 

  • Network security controls: Employ network security controls, including intrusion detection/prevention systems (IDS/IPS), next-generation firewalls (NGFW), and secure web gateways (SWG), to monitor network traffic for signs of malicious activity and block suspicious connections or payloads associated with Zero Click attacks

  • Network segmentation: Implement network segmentation to compartmentalize sensitive systems and limit the lateral movement of attackers within the network. Use firewalls, VLANs, and access control lists to enforce segmentation and restrict unauthorized access to critical assets

  • Zero-Trust Architecture (ZTA): Adopt a zero-trust security model that assumes a hostile environment and verifies every access attempt, regardless of the source or location. Implement strong authentication mechanisms, least privilege access controls, and continuous monitoring to enforce granular access policies and prevent unauthorized access to critical resources

• Incident Response Plans: Having robust incident response plans (IRPs) in place is crucial for organizations to effectively respond to zero-click attacks and other security incidents. IRPs outline the procedures and protocols for detecting, assessing, containing, mitigating, and recovering from security breaches or incidents promptly and efficiently

Conclusion

Zero Click attacks represent a significant challenge in cybersecurity, as they allow attackers to execute malware without any user interaction, making them harder to detect and mitigate. This article has explored various techniques used in Zero Click attacks and highlighted the difficulties in defending against them.  Defending against these attacks requires a comprehensive approach that includes preventive, detective, compensating, and corrective measures. 

Proactive defenses such as vulnerability management, virtualization, content filtering, and network security controls can help reduce the attack surface and prevent exploitation. Reactive measures such as endpoint protection, and having proper incident response plans can help detect and respond to these types of cyberattacks effectively.

Ultimately, organizations must adopt a defense-in-depth strategy, leveraging multiple layers of security controls to mitigate the risks posed by Zero Click attacks. By staying vigilant, implementing best practices, and having robust incident response plans in place, organizations can strengthen their cybersecurity posture and protect against the ever-evolving threat landscape posed by these attacks.