Penetration tests often reveal serious gaps in security that organisations may not be aware exist. These weaknesses can leave important systems and data exposed to hackers if not addressed quickly. The top 10 most common security flaws found during penetration testing include weak passwords, unpatched software, poor network segmentation, and vulnerabilities in web applications such as injection flaws and cross-site scripting.
Many of these issues are preventable but still appear regularly across businesses of all sizes. Attackers commonly target simple mistakes like default credentials or misconfigured systems, making it vital to understand and fix these flaws. By knowing what vulnerabilities are most frequently discovered, companies can take practical steps to reduce their risk and strengthen their overall security.
Overview of Security Flaws in Penetration Tests
Security flaws in applications and systems can expose organisations to serious threats. Penetration testing aims to uncover these vulnerabilities so that they can be fixed before attackers exploit them. Key areas include understanding what vulnerabilities are, the purpose of penetration tests, and how the OWASP Top 10 serves as an important guide in application security.
Understanding Vulnerabilities
A vulnerability is a weakness or flaw in software, hardware, or network security that could be exploited by attackers. Common examples are weak passwords, outdated patches, and insecure configurations. These issues can allow unauthorised access, data theft, or disruption of services.
Some vulnerabilities are technical, like SQL injection or cross-site scripting (XSS), which affect how applications handle input. Others are procedural, such as failing to segment networks or using default credentials. Even simple oversights, like missing security updates, can lead to serious risks.
Recognising and addressing these vulnerabilities is essential for maintaining a secure environment. Regular assessments help identify these flaws before they can be targeted.
Role of Penetration Testing
Penetration testing is the process of simulating attacks against systems, networks, or applications to find weaknesses. Security professionals use real-world attack methods to test if defences can stand up to actual threats. This helps in discovering both common and hidden vulnerabilities.
During a pen test, testers may look for issues like poorly configured servers, lack of access controls, or exposed APIs. The results provide organisations with a clear view of their current security posture. With these findings, they can prioritise fixes based on risk.
Penetration testing is not just a one-time activity. It should be repeated regularly to catch new vulnerabilities as systems change and threats evolve.
Significance of the OWASP Top 10
The OWASP Top 10 is a list of the most critical web application security risks identified by the Open Web Application Security Project (OWASP). It acts as a practical guide for appsec professionals, showing which issues need the most attention.
Risks on the list include injection flaws, broken authentication, sensitive data exposure, and security misconfiguration. The OWASP Top 10 is updated regularly to reflect current attack trends and emerging threats.
By focusing on the OWASP Top 10, organisations can quickly address the most common and dangerous vulnerabilities in their web applications. This helps in setting priorities for both development and testing teams and improves overall security.
Broken Access Control
Broken access control is one of the most widespread and severe security gaps found in penetration tests. These flaws occur when applications do not properly restrict user permissions, allowing attackers to gain access to data or functions they should not be able to reach.
Common Exploits in Access Controls
Attackers often take advantage of insecure direct object references (IDORs), which happen when an application does not check if a user is allowed to access a resource, such as another user's profile or files.
Another frequent vulnerability is when role-based access controls are missing or poorly implemented. This can allow normal users to access admin features simply by guessing or manipulating URLs and parameters.
Access control flaws can also arise from lax permission settings, such as when APIs or endpoints are not protected, enabling unauthorised users to create, modify, or delete sensitive data.
Penetration testers often find these issues when accounts are not separated by privilege or when session management does not enforce access rules. Table summarising key problems:
| Vulnerability Type | Example Impact |
|---|---|
| IDOR | Access to other users' data |
| Privilege escalation | Gain admin permissions |
| Insecure APIs | Unauthorised data changes |
Mitigating Broken Access Control
Implementing the principle of least privilege is critical. Users should only be granted the minimum permissions needed to do their job, and all other actions should be denied by default.
Consistent use of access control checks on both the client and server sides helps ensure that requests are verified, even if inputs are manipulated. Privilege checks should occur for every sensitive action or data access.
Audit trails and logging can quickly help detect suspicious access attempts. Regular reviews of access controls, especially in endpoints and APIs, can prevent security gaps from going unnoticed.
Automated and manual testing should verify that users cannot perform unauthorised actions. Keeping access rules up to date as application features change is essential for ongoing protection.
Authentication and Session Management Issues
Weak authentication and poor session management are among the most exploited weaknesses in modern applications. Attackers often exploit these flaws to gain access to sensitive accounts, bypass protections, or maintain control over user sessions.
Broken Authentication
Broken authentication happens when systems fail to properly check user identities. Attackers take advantage of these failures to take over user accounts or escalate privileges.
Common issues include missing limits on login attempts, weak password recovery processes, and predictable login URLs. Systems might not log out users correctly or may allow session tokens to be reused after logout. These risks make unauthorised access more likely if attackers obtain valid login data or session tokens.
Examples of broken authentication flaws:
- Allowing unlimited failed login attempts (enabling brute force attacks)
- Exposing detailed error messages that help attackers learn about valid usernames and passwords
- Storing or transmitting passwords in plain text
Organisations should regularly review how authentication is handled in their applications and follow security best practices throughout the login and session process.
Weak Passwords and Default Credentials
Many systems are deployed with default admin credentials or allow users to choose easily guessed passwords. Attackers check for these simple weaknesses first because they often give immediate access.
Common default credentials:
| Username | Password |
|---|---|
| admin | admin |
| root | password |
| user | 123456 |
Password policies that allow short, simple, or dictionary-based passwords increase the risk. The use of common passwords like “password”, “123456”, or a company name are still frequently seen.
Attackers use automated tools to try thousands of password combinations very quickly. Changing all default credentials and enforcing strong password requirements help keep intruders out of the system.
Session Handling Best Practices
Session management is crucial. Poor session handling leads to session hijacking, where attackers steal valid session tokens and impersonate users.
Common flaws include predictable or unprotected session IDs and failing to expire sessions after logout or a period of inactivity. Not using secure cookies or transmitting session IDs over unencrypted connections exposes them to theft.
Best practices:
- Use unique and random session tokens
- Set session cookies to be HttpOnly and Secure
- Always expire sessions properly after logout or timeout
- Avoid exposing session tokens in URLs
Implementing these steps makes it harder for attackers to hijack user sessions and pose as legitimate users.
Multi-Factor Authentication
Multi-factor authentication (MFA) requires users to provide more than one method to prove their identity. Adding MFA greatly increases the difficulty of unauthorised access, even if passwords are compromised.
MFA combines something the user knows (like a password), something they have (such as a phone or token), and sometimes something they are (biometrics). Common methods include SMS codes, authenticator apps, or hardware keys.
Benefits of MFA:
- Blocks most automated attacks and many phishing techniques
- Reduces the impact of stolen credentials
- Provides an extra layer of security for sensitive accounts
Organisations should add MFA wherever possible to prevent identification and authentication failures, especially for administrative accounts or systems with sensitive data.
Injection Attacks
Injection attacks are one of the most severe and frequent vulnerabilities found during penetration tests. Attackers use these flaws to send untrusted data into a system, often causing it to behave in unexpected ways or expose sensitive information.
SQL Injection
SQL injection is a critical vulnerability that affects web applications relying on databases. When user input is not properly filtered or validated, attackers can insert malicious SQL code into queries. This can allow them to read, modify, or delete data from the database.
For example, a login form that directly passes user input into an SQL query can be tricked with specially crafted text. This can give attackers access to user accounts without a valid password.
Key risks of SQL injection include:
- Data theft or loss
- Unauthorised account access
- Database corruption
Using parameterised queries and stored procedures can help prevent SQL injection. Regular testing and code reviews are also effective ways to reduce exposure.
Cross-Site Scripting (XSS)
Cross-Site Scripting (XSS) is another common injection flaw mainly affecting web browsers. XSS happens when attackers are able to inject malicious scripts into web pages that are then viewed by other users. These scripts can steal session cookies, redirect users, or display unwanted content.
XSS usually occurs when websites fail to validate, encode, or clean up user-supplied data before showing it in the browser. For instance, a comments section that displays raw user input without filtering can be exploited. Attackers might inject script tags that run unwanted JavaScript code.
Main consequences of XSS:
- Identity theft
- Account hijacking
- Spreading malware
Defending against XSS includes escaping output, validating input, and adopting a strict Content Security Policy (CSP).
Other Injection Flaws
Besides SQL injection and XSS, several other injection flaws are regularly discovered. These include command injection, LDAP injection, and XML injection. Each allows attackers to inject code or commands into different parts of a system.
Command injection lets attackers run operating system commands with the application's privileges. LDAP or XML injection targets directory services or data processing, often leading to information leaks.
To reduce the risk from these injection flaws, developers should validate all inputs, use safe API calls, and minimise the application's privileges wherever possible. Automated security testing tools can also help find and fix these vulnerabilities before attackers do.
Sensitive Data Exposure and Cryptographic Failures
Sensitive data exposure allows attackers to access confidential information, such as passwords or personal records. Cryptographic failures often happen when data is not protected correctly, putting both users and organisations at risk.
Sensitive Information Risks
Sensitive data includes details like names, addresses, credit card numbers, and passwords. Attackers target these because they can use or sell the data. When organisations store this information without enough protection, such as weak passwords or missing security controls, data breaches are more likely.
Unauthorised access can happen if files or databases are not set with proper permissions. File upload flaws sometimes let attackers retrieve entire password databases. Personal details can also be leaked through web application errors, making them visible to anyone on the internet. It is important for organisations to know what sensitive data they have and secure it with care.
Encryption and Hashing
Encryption turns readable information into coded text so only authorised users can read it. Hashing scrambles data, often used for passwords, so they cannot be easily reversed. When cryptographic methods are weak, or encryption is not used, attackers can steal and understand the information.
A common mistake is storing passwords using unsalted hashes. This means if attackers access the hash, they can use rainbow tables (lists of pre-calculated hash values) to find the original password. Best practice is to use strong encryption (like AES) and salted cryptographic hashes (such as bcrypt or Argon2). Regularly updating and testing cryptographic methods helps keep protection strong.
HTTPS and Data Protection
Websites often transmit information, like login details or payment data, between users and servers. Using HTTPS instead of HTTP encrypts this data during transit. If sites fail to use HTTPS, attackers can intercept sensitive information by “listening” to network traffic, especially on public Wi-Fi.
Many security tools warn users when they enter data on non-secure connections. Organisations must make sure all pages, especially those with forms for sensitive details, use HTTPS. A valid SSL/TLS certificate and up-to-date protocols defend against interception and help keep user data private. HTTPS is now considered a basic requirement for any secure website.
Security Misconfigurations
Security misconfigurations remain a major issue in penetration tests, often leading to serious security gaps. Problems can range from default settings left unchanged to missing updates and weak cloud or API controls.
Common Misconfiguration Examples
Security misconfiguration occurs when systems or applications are not set up securely. This might include using default usernames and passwords, unnecessary services running, or directory listing being enabled on web servers.
Unpatched systems are another common issue. Attackers can exploit old software with known bugs if updates are missed. On web servers, weak permissions on files or folders can let unauthorised users view or change sensitive data.
Admins often forget to disable debug modes or sample files after development. If attackers find these, they can gain a deep understanding of how the application works. It is also common to see error messages that give away too much information about the system.
| Example | Risk |
|---|---|
| Default credentials | Easy remote access for attackers |
| Unpatched software | Exploitation of known vulnerabilities |
| Directory listing | Exposure of system files |
| Verbose error messages | Info disclosure for further attacks |
Cloud and API Misconfigurations
Cloud environments and APIs offer flexibility and speed, but misconfigurations introduce significant risks. Common mistakes include overly broad permissions, public cloud storage buckets, and exposed API keys.
Cloud storage, such as Amazon S3 buckets, can accidentally be left open to the internet, revealing data to anyone. Setting insecure access controls for cloud services allows users to perform actions they should not, increasing the chance of data leaks or destruction.
Unsecured APIs can expose sensitive data or system functions directly to the world. If authentication or rate limiting is not set up correctly, attackers can abuse the APIs. Failing to encrypt communication between services leaves data open to interception.
Regular auditing and the use of automated scanning tools are necessary to detect these misconfigurations and minimise risks in both cloud and API settings.
Vulnerable and Outdated Components
Outdated or vulnerable components in software often provide easy entry points for attackers. Keeping software, third-party libraries, and all dependencies updated is a crucial step in maintaining strong security.
Third-Party Libraries and Components
Third-party libraries and components allow developers to add features quickly. However, these libraries might include vulnerabilities or bugs that an attacker can exploit.
Software projects often rely on many external libraries. If any are outdated or have known security issues, attackers can use them to gain unauthorised access, steal data, or launch attacks against users. For example, well-known vulnerabilities such as Heartbleed and Log4Shell were both found in widely used components.
A regular review of all third-party dependencies is necessary. It is important to monitor which versions are being used and whether any new security advisories have been released for those components. Developers should prefer libraries that are actively maintained and reject those that have not been updated for long periods.
Patch Management Strategies
Effective patch management is essential to guard against known vulnerabilities in both software and its components.
When new security updates or patches are released, organisations should have a clear and repeatable process to roll out these updates quickly. Delays in applying patches to operating systems, applications, or libraries can leave a window of time where systems remain exposed to threats.
A patch management process typically involves:
- Maintaining a full list of software and components in use.
- Monitoring for updates and relevant security bulletins.
- Testing patches in a staging environment.
- Rolling them out to production quickly after testing.
Automation tools and centralised update management systems help organisations apply patches efficiently and reduce human errors.
Software Composition Analysis
Software Composition Analysis (SCA) tools automatically check which components and libraries a project uses.
SCA helps teams identify components with known vulnerabilities by scanning software dependencies and matching them with vulnerability databases such as the National Vulnerability Database (NVD). These tools highlight outdated libraries and warn of any security risks in use.
SCA can also produce detailed reports and offer recommendations on safer versions to use. Teams should run SCA scans regularly, both during development and before deploying any code to production. Integrating SCA into the build and deployment process helps catch risky components early and supports a proactive, rather than reactive, approach to security.
Insufficient Logging and Monitoring
Many security breaches go unnoticed because of weak or missing logging and monitoring systems. Attackers often exploit these gaps to move within networks without being detected or stopped.
Security Logging Failures
Logging should capture important information such as login attempts, file changes, failed access, and privilege escalation. When logs are missing these details, it becomes very hard to trace events or understand the actions leading to a security incident.
Common issues include incomplete logs, failure to record user actions, or missing data like timestamps and IP addresses. Poor log storage, such as saving logs in unprotected locations, also increases risk. Logs need to be protected from tampering so attackers cannot cover their tracks.
Many organisations do not use application security tools that analyse logs for signs of attack or misuse. Without these tools, suspicious activity often remains unnoticed. Even when logs exist, if they are not reviewed, potential threats can pass by without alerting anyone.
Detection and Response
Logging alone is not enough. Real security comes from active monitoring and a plan for quick response. Attackers rely on slow or absent monitoring to spend more time inside systems undetected.
Effective detection requires monitoring tools that alert staff when something unusual happens, like repeated failed logins or unauthorised access to important files. Quick alerts allow for a faster response, helping stop attacks before they do major damage.
To respond well, organisations need clear procedures for handling alerts from logging and monitoring systems. This process should involve investigating alerts, containing threats, and fixing vulnerabilities. Regular testing and updating of monitoring and response processes makes it harder for attackers to succeed.
Advanced and Emerging Security Risks
Modern systems face a range of security threats that go beyond the most common flaws. These risks often exploit weaknesses in software design, data handling, and system behaviour, making traditional defences less effective.
Insecure Design and Deserialisation
Insecure design exposes systems to attacks before technical controls can stop them. This is often caused by missing secure design patterns or a lack of threat modelling. Attackers can take advantage of weak architecture decisions, such as poor validation of input or insufficient separation of duties.
Insecure deserialisation is a specific flaw where attackers send unsafe data that an application processes and converts. This can allow them to execute code, gain unauthorised access, or cause system failures. This risk affects many common frameworks and languages.
Prevention includes careful use of libraries that process serialised data, avoiding deserialisation of untrusted objects, and designing the system with security in mind from the start. Regular code reviews and threat modelling can help find and fix these flaws.
Denial of Service Attacks
Denial of Service (DoS) attacks aim to make a service or network unavailable by overwhelming it with traffic or exploiting specific flaws. Attackers might flood systems with requests, exhaust resources, or trigger software bugs that crash services.
DoS attacks are especially damaging for public-facing websites and APIs. Distributed Denial of Service (DDoS) takes this further by using many sources at once, making it harder to defend.
Firewalls, rate limiting, and using defence-in-depth strategies such as redundant systems can help reduce the risk. Systems should be tested for bottlenecks and weak points to improve resilience against such attacks.
Software and Data Integrity Failures
Software and data integrity failures occur when updates, code, or data can be changed in unauthorised ways. Attackers might insert malicious code into software updates or change stored data to compromise applications. This risk increases with weak update processes or when important files are not checked for changes.
Protecting integrity involves signing code and updates, using secure transmission methods, and applying strict controls around who can change software or data. Systems can monitor for unexpected changes and alert teams about possible tampering.
Keeping software up to date with verified sources and using multi-person approval for critical changes also helps prevent these failures.
XML External Entities (XXE)
XML External Entities (XXE) vulnerabilities happen when applications process XML input that includes references to external entities. Attackers can use XXE to read files on the server, access internal networks, or cause the application to crash.
This flaw often exists in older XML parsers or when secure configuration is missing. Disabling external entity processing, patching libraries, and validating XML inputs are key defences.
Security teams should review parsers to ensure safe settings and avoid exposing systems to external file access through XML. Regular testing can help detect and mitigate XXE risks before attackers exploit them.
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