Imagine your organization’s digital fortress – now picture a thousand hidden doors, each a potential entry point for cyber threats. In the world of cybersecurity, these doors are known as ‘external attack surface vulnerabilities’ and understanding them is the first step to locking them down.

External attack surface vulnerabilities are the weak points of a company’s network that can potentially be exploited by malicious actors. These include public-facing web servers, email servers, and other services. Companies must be aware of the risks associated with these vulnerable points, and take the appropriate steps to protect their networks from attacks.

In this article, we take a look at the most common external attack surface vulnerabilities, and steps you can take to minimize them with an External Attack Surface Management (EASM) solution.

What is an external attack surface?

If your organization’s digital presence is a fortress, the external attack surface is everything visible from the outside. It includes public-facing assets like web applications, API endpoints, email and DNS servers, VPN gateways, cloud environments, subdomains, and even inadvertently exposed admin panels or development systems.

In short, your external attack surface is all the entry points a malicious actor could discover and attempt to exploit.

These exposed assets often lie outside the scope of traditional internal security controls, turning them into prime targets for attackers. Left unmonitored or misconfigured, they can serve as weak links providing criminals with easy paths to launch attacks.

Top 10 most common external attack surface vulnerabilities

1. Misconfigured access controls

A recent report found that 80% of security exposures are caused by identity and credential misconfigurations, with 56% of exposures that impact critical assets found within cloud platforms. These numbers are likely to accelerate further as cloud adoption continues to increase.

One recent case really drives home the point. In a breach affecting ESHYFT, a New Jersey-based HealthTech company, a misconfigured AWS S3 bucket exposed over 86,000 healthcare staff records, including sensitive PII and medical documents protected under HIPAA.

2. Unpatched software and hardware

Unpatched software is another major attack vector for malicious actors. Whether it’s an operating system, web browser, or even a piece of hardware like a router, if it isn’t up-to-date with security patches and updates, attackers may be able to exploit the vulnerabilities.

For example, a recent report revealed that 50% of enterprise-managed Windows devices are still running Windows 10, continuing to rely on an OS that will reach end‑of‑support in October 2025.

3. Open ports and services

Open ports can pose serious risks to IT environments, with threat actors exploiting these vulnerabilities through techniques like spoofing, credential sniffing, and other malicious methods.

Several specific ports have been identified as particularly susceptible to cyberattacks, such as ports 20 and 21 (FTP), port 22 (SSH), port 3389 (Remote Desktop), but many others are vulnerable as well.

For example, WannaCry ransomware that exploited SMB vulnerability on, and ongoing campaigns targeting Microsoft’s Remote Desktop Protocol, illustrate the real-world consequences of these vulnerabilities.

4. Weak network perimeters

A strong network perimeter acts as the first line of defense against external threats. Without proper security measures in place, malicious actors can easily penetrate the network, leading to unauthorized access, data breaches, or even a complete system takeover.

In one of the most sophisticated attacks in recent history, malicious actors compromised the SolarWinds Orion software by inserting a vulnerability into the software’s updates. Weak network perimeters and lack of proper monitoring enabled the attackers to move laterally through the networks of thousands of SolarWinds customers, including several U.S. government agencies.

5. Phishing and social engineering

The human element still makes up an overwhelming number of incidents, even as enterprises continue to safeguard critical infrastructure and increase training on cybersecurity protocols.

According to Verizon’s annual Data Breach Investigations Report (DBIR) 2025, social engineering accounted for 22% of external actor breaches, remaining a significant threat to businesses across all industries.

6. Insecure APIs

As organizations continue to rely more on interconnected applications and cloud-based services, the security of APIs has become a focal point in cybersecurity strategies. APIs are a lucrative target for hackers seeking to gain access to personally identifiable information (PII) and orchestrate sophisticated social engineering attacks.

In June 2021, a vulnerability in Twitter’s API was discovered and subsequently patched, but it later led to significant consequences. A hacker claimed to have the personal data of 400 million users for sale on the dark web in December, and the account details and email addresses of 235 million users were released for free. The breach exposed information such as users’ account names, handles, creation dates, follower counts, and email addresses.

7. Outdated or insecure encryption

Encryption is an essential part of any security strategy. However, outdated or insecure encryption protocols can present major risks.

A security incident involving a compromised Microsoft key, attributed to the Chinese threat actor Storm-0558, had wide-reaching implications. Researchers found that the compromised key was not limited to Outlook.com and Exchange Online but could also have been used to forge access tokens for various Azure Active Directory applications, such as SharePoint, Teams, and OneDrive.

While Microsoft mitigated the risk by revoking the affected key, detecting forged tokens may still be challenging for customers due to the lack of logs in the token verification process. The incident underscores the immense power of identity providers’ signing keys and calls for greater security and transparency in protecting such keys to prevent similar future occurrences and reduce their potential impact.

8. Third-party dependencies

External libraries, offering the advantage of extra functionality without the need to build from scratch, come with the drawback of limited organizational control over their security. This lack of control means that vulnerabilities within these components can jeopardize the entire system.

Even trusted vendor platforms introduce risks when employees are manipulated into granting access. A striking example is the recent vishing campaign targeting Salesforce environments, impacting organizations including Google, Chanel, and Air France–KLM. In these incidents, attackers impersonated IT support via phone calls and tricked users into installing malicious Salesforce tools. This covert access enabled them to extract sensitive customer-support records—such as contact details and loyalty information—from CRM systems.

9. DDoS attacks

DDoS (Distributed Denial of Service) attacks remain one of the most common and disruptive external attack surface vulnerabilities. By overwhelming public-facing assets—such as websites, APIs, or DNS servers—with massive volumes of traffic, attackers can cause prolonged service outages and degrade performance, often with little technical sophistication required.

These attacks target exposed infrastructure that’s accessible over the internet, making them a persistent threat for any organization with online services.

10. Shadow IT

Shadow IT refers to hardware or software used within an organization without explicit IT department approval; think forgotten cloud instances, unsanctioned collaboration tools, or third-party services quietly spun up by business units. These assets often operate outside the visibility of security teams, creating blind spots that attackers can exploit.

A Forbes‑Insight survey found that one in five organizations have experienced a cyber breach directly attributable to shadow IT. These unmanaged assets frequently lack proper configuration, patching, and monitoring, making them easy targets for attackers seeking low-hanging fruit.

How to reduce external attack surface vulnerabilities

Exploited vulnerabilities can lead to substantial damages including financial losses, reputational damage, and operational disruptions. That’s why it’s critical to adopt a proactive approach to minimizing external attack surface vulnerabilities. Here are some key actions you can take to help:

1. Map your external attack surface

The first step to securing your environment is understanding what you have. By performing comprehensive asset discovery, you can identify and catalog all internet-facing systems. including domains, subdomains, IP addresses, web applications, and cloud infrastructure. This visibility is essential for establishing a baseline and uncovering forgotten or unknown assets that may be vulnerable.

2. Set up automated continuous scanning

Your organization’s digital footprint is constantly changing, which means its exposure to threats is too. Continuous monitoring of your external attack surface helps detect new risks as they appear, from unauthorized changes to newly exposed services. With 24/7 scanning in place, security teams can react quickly to changes and reduce response times.

A modern External Attack Surface Management (EASM) solution can help with this, providing round-the-clock monitoring to ensure all potential threats are detected early.

3. Run regular vulnerability assessments

Vulnerability assessments help identify and prioritize weaknesses across your internet-facing assets before attackers do. By regularly scanning for known issues and ranking them based on severity and exploitability, organizations can focus their resources on remediating the most critical threats and stay ahead of potential breaches.

4. Perform configuration assessments

Misconfigurations remain one of the most common causes of data exposure. Regular assessments of system and application configurations make sure that externally facing assets are securely set up in line with industry best practices and compliance standards. This reduces the chance of accidental exposure and strengthens your defensive posture.

5. Monitor for known CVEs

Known vulnerabilities—especially those with public exploits—represent a major risk to unpatched systems. Monitoring your environment for Common Vulnerabilities and Exposures (CVEs) allows you to identify outdated or unsupported software, prioritize patches, and block common attack paths.

Vulnerabilities tied to older technologies are particularly attractive to threat actors and can be exploited to cause service outages or gain access to sensitive data.

To help mitigate these threats, the Outpost24 EASM solution calculates the priority around every CVE observation and notifies you automatically when they appear for your scope. Besides the priority score, each observation contains a specific help text detailing the observation, risk and proposed recommendation.

Minimize external attack surface threats with Outpost24 EASM

Outpost24’s EASM platform gives you the visibility and control needed to uncover hidden exposures, detect vulnerabilities, and reduce cyber risk across your entire digital footprint. By combining 24/7 monitoring, automated asset discovery, continuous vulnerability and configuration assessments, and real-time attack surface scoring, it empowers your security team to stay ahead of threats—before they become breaches.

Take the first step toward smarter, stronger perimeter security. Start your free trial today and explore how Outpost24 can help you regain control of your external attack surface.