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7 Best Practices for Security Code Reviews

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Data breaches and cyber threats are becoming increasingly common and expensive to deal with. This is one of the reasons we have recently released Codacy Security. Protecting code has to now come at the forefront of every software development and maintenance strategy, ensuring the integrity and availability of applications and safeguarding sensitive data against unauthorized access and exploitation.

Here, we take you through what we see as the seven best practices for conducting effective code reviews with security in mind, allowing you to strengthen your software defenses. Let’s dive in!

1. Establish Clear Objectives and Involve Diverse Reviewers for Enhanced Security Code Review

Effective security code review begins with setting precise objectives. Clear goals aligned with your project's Service Level Agreement (SLA) ensure a focused review process. These objectives range from detecting vulnerabilities like SQL injection and cross-site scripting to improving overall code security posture. Such a security code review SLA might look like this:

  1. Vulnerability Identification: Detect and report all instances of SQL injection, cross-site scripting (XSS), and insecure direct object references within the codebase.

  2. Resolution Timeframe: Ensure that identified critical vulnerabilities are addressed and resolved within 15 business days of detection.
  3. Compliance Standards: Adhere to [specific industry standard, e.g., OWASP Top 10], ensuring the codebase meets these security benchmarks.

  4. Review Frequency: Conduct comprehensive security code reviews quarterly, with interim reviews upon significant code updates or feature releases.

Involving diverse reviewers is crucial for a comprehensive security code review. Assemble a team that varies in programming language expertise and experience levels and roles–including developers, QA engineers, and security specialists. This variety enriches the review process by bringing different perspectives facilitating the identification of a broader range of potential security weaknesses. According to our 2024 State of Software Quality report, 32% of developers surveyed have dedicated time slots specific to conducting code reviews, with another 32% integrating code reviews into their daily routine.

Beyond technical expertise, consider including non-technical stakeholders, such as product managers. Their insights can help understand security issues' broader business and user impact. This holistic approach ensures the security code review addresses technical and business-centric security concerns.

When selecting reviewers, consider factors like their experience with similar projects, understanding of security best practices, and ability to think like potential attackers. It’s not just about finding experts but also about assembling a team that complements each other’s skills and perspectives.

Finally, establish metrics or indicators to assess the effectiveness of the code review security efforts. These could include the number of vulnerabilities identified and resolved, the improvement in code quality scores, or even the speed at which security issues are addressed post-review. Tracking these metrics over time can provide valuable insights into the efficacy of your security code review process and areas for future improvement.

By setting clear objectives, involving a diverse team, and measuring outcomes, you can significantly enhance the effectiveness of your security code review process.

2. Sanitize and Validate All Input for Robust Code Security

A fundamental aspect of security code review is treating every input as a potential threat. This includes direct user inputs, data received from third-party sources, and internal inputs controlled by your team. To bolster your application against common threats like SQL injections or XSS attacks, it’s essential to validate and sanitize all inputs rigorously.

Validation should go beyond just checking the format. It must comprehensively assess each input’s range, size, file type, and name, ensuring they meet the defined criteria for safe and expected data. Contextual validation is vital, with specific checks tailored to different data types, like email addresses or file uploads.

Consider a web application that accepts file uploads from users. In this scenario, a simple file type check isn't enough:

import os
from werkzeug.utils import secure_filename
from flask import request

ALLOWED_EXTENSIONS = {'png', 'jpg', 'jpeg', 'gif'}

def allowed_file(filename):
    return '.' in filename and \
           filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS

@app.route('/upload', methods=['POST'])
def upload_file():
    if 'file' not in request.files:
        return 'No file part'
    file = request.files['file']
    if file.filename == '':
        return 'No selected file'
    if file and allowed_file(file.filename):
        filename = secure_filename(file.filename)
        file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
        return 'File successfully uploaded'
        return 'Invalid file type'

This code snippet includes checks for file presence and validity and ensures the file extension is within the allowed set. secure_filename is used to sanitize the filename. Such detailed checks in the security code review process can significantly reduce the risk of malicious file uploads.

Incorporating automated code security tools and libraries in your security code review process can significantly streamline and enhance input validation. These tools help identify vulnerabilities that might be overlooked and ensure consistent application of validation rules.

However, validation is not a one-time task. Continuous monitoring and updating of validation rules are crucial in a dynamic threat landscape. Regularly revisiting and refining these rules as part of your code review security practices helps effectively address new and evolving threats.

Moreover, input validation should be integral to broader secure coding practices. You can create a more resilient and secure application by embedding these practices within your development process. This proactive approach in your security code review ensures that all inputs are thoroughly scrutinized before they are stored or used anywhere in your codebase, thus safeguarding your application from a wide array of potential security vulnerabilities.

3. Protect Sensitive Data with Advanced Measures

Protecting sensitive data, such as personal information and credit card numbers, demands additional layers of security. To ensure robust protection, use established encryption standards like AES for data at rest and RSA for data in transit. Implement cryptographic hashing algorithms such as SHA-256 for password storage.

Implement stringent access control measures. This involves authentication and precise authorization to ensure that only authorized personnel access sensitive data.

Be prepared with a comprehensive data breach response plan. Quick and effective actions can mitigate damage significantly in case of a breach. Here’s a possible data breach response plan:

  • Identification and Assessment
      1. Detect and confirm the breach.
      2. Assess the scope and impact on data and systems.
  • Containment
      1. Immediately isolate affected systems to prevent further data loss.
      2. Secure backups and other unaffected systems.
  • Eradication
      1. Identify and eliminate the cause of the breach (e.g., malware removal, system updates).
  • Notification
      1. Inform internal stakeholders and legal teams.
      2. Notify affected individuals and regulatory bodies as required by law.
  • Recovery
      1. Restore systems and data from backups.
      2. Reinforce security measures to prevent recurrence.
  • Post-Incident Analysis
      1. Conduct a thorough investigation to understand how the breach occurred.
      2. Document lessons learned and update security policies and protocols accordingly.
  • Ongoing Monitoring
      1. Implement enhanced monitoring to detect future incidents early.
  • Communication Plan
      1. Prepare internal and external communication strategies.
      2. Maintain transparency with stakeholders and customers.
  • Legal Compliance and Documentation
      1. Ensure all actions comply with relevant data protection laws.
      2. Keep detailed records of the breach response for legal and regulatory purposes. 
  • Review and Update the Plan
    1. Regularly review and update the response plan based on new threats, vulnerabilities, and organizational changes.

Remember, the specific steps and details in your Data Breach Response Plan may vary depending on your organization's size, the nature of data handled, and the regulatory environment.

4. Implement Secure Authentication in Security Code Review

Secure authentication is a cornerstone of security code review. It's crucial to verify user identity robustly. Best practice dictates treating every user as unauthenticated until they prove their identity with the correct credentials. Enforcing password complexity is just the start. Include at least one uppercase character, one lowercase character, one digit, one unique character, and a specific length. Recognize that complex passwords can be challenging to remember, thus encouraging the use of password managers.

However, more than password-based authentication is needed. Implement multi-factor authentication (MFA) as an additional layer of security. This could involve a combination of something the user knows (a password), something they have (a mobile device), and something they are (biometric data). To implement Multi-Factor Authentication (MFA) in JavaScript, you can use a third-party library like Authy. Authy provides a straightforward API to integrate MFA into your application. Here's an example using Node.js:

const authy = require('authy')('Your_Authy_API_Key');

// Register a user
authy.register_user('user_email@example.com', 'user_phone_number', 'country_code',
function (registrationError, registrationResponse) {
    if (registrationError) {

    } else {
        console.log("Authy ID: ", registrationResponse.user.id);
// Request an SMS token
authy.request_sms('Authy_ID', function (smsError, smsResponse) {
    if (smsError) {
    } else {
        console.log("Token sent successfully.");
// Verify a token
authy.verify('Authy_ID', 'Token_Entered_by_User', function (verifyError, verifyResponse) {
    if (verifyError) {
    } else if (verifyResponse.success) {
        console.log("Token verified successfully.");
    } else {
        console.log("Invalid token.");

In this example:

  • Replace 'Your_Authy_API_Key' with your actual Authy API key.
  • The register_use function is used to register a new user with Authy.
  • The request_sms function requests an SMS token for the user.
  • The verify function verifies the token provided by the user.

You can also consider alternatives to traditional passwords, such as biometric authentication, single sign-on (SSO) systems, or authentication apps. These can offer greater security and user convenience.

Educating users on secure password practices is vital. Encourage regular password changes and inform users of the risks of password reuse. In your code review security process, ensure that your application enforces these password policies effectively.

Integrate account lockout mechanisms to thwart brute force attacks. After a predetermined number of failed login attempts, temporarily lock the account and alert the user.

Monitoring and alerting are also crucial. Set up systems to detect unusual login patterns or locations and alert users and administrators of potential security breaches. This proactive approach is essential in the rapidly evolving landscape of cyber threats.

Incorporating these elements in your security code review process ensures a robust authentication system, significantly enhancing the overall security of your application.

5. Give the Least Privilege Possible Using Role-Based Access Control

Ensuring that each user has only the necessary access rights in security code review is crucial. This is where Role-Based Access Control (RBAC) becomes essential. RBAC is a method of restricting system access to authorized users based on their role within an organization. It allows for a more granular and manageable approach to assigning privileges.

Under RBAC, roles are created according to job competency, authority, and responsibility within the organization. Each role is assigned specific access rights, ensuring no user has more access than needed for their function. This adherence to the principle of least privilege minimizes potential vulnerabilities.

Imagine a company with different departments like Sales, HR, and IT. Each department requires access to different systems and data.

  • Roles: Define roles such as Sales Manager, HR Executive, IT Administrator.

  • Permissions: Assign permissions based on roles. For instance, HR Executives can access employee records but not financial data; Sales Managers can access customer data but not HR records.

  • Users: Assign users to these roles. John, an HR Executive, will have access to HR systems but not sales databases.

In this way, RBAC ensures users only access information necessary for their job, reducing the risk of unauthorized access or data breaches.

In addition to RBAC, dynamic access control systems can adjust user permissions based on specific contexts or conditions in real time. This adds a layer of flexibility and security, particularly in complex environments.

Regular audits and updates to access control configurations are necessary to maintain adequate security. These audits ensure that changes in roles, responsibilities, or the system itself don't lead to unnecessary permissions being granted.

Integrating the least privilege principle into broader organizational security policies reinforces a culture of security awareness. It’s about setting up the system and maintaining it as part of ongoing security practices.

6. Stay on Top of Emerging Threats

Staying abreast of emerging threats is paramount for effective security code reviews. One critical step is implementing structured training programs. These programs should provide continuous education on security vulnerabilities and countermeasures, ensuring reviewers are well-equipped to identify and mitigate new risks.

Collaboration with security communities is another vital strategy. Active participation in security forums, online communities, and conferences enables code reviewers to exchange knowledge, learn from real-world incidents, and stay updated on cutting-edge security trends. This collaborative approach enriches the team's collective expertise and fosters a proactive security culture.

Regular security assessments are crucial for testing an organization's preparedness against these evolving threats. Periodic security drills, penetration testing, and vulnerability assessments can reveal how new threats might impact the current infrastructure and codebase. These assessments guide ongoing improvements in security strategies and code review practices.

By embracing continuous training, community collaboration, AI and ML integration, and regular security assessments, organizations can ensure their code review processes are robust and adaptive to the ever-evolving landscape of software security threats.

7. Automatically Test Your Code with Static Analysis Tools

Leveraging automated code analysis tools that can focus on security will significantly enhance the efficiency and effectiveness of code reviews.

By statically looking at your code, these tools will quickly identify common security-related issues and help pinpoint potential vulnerabilities. For example, the Codacy Quality tool can highlight issues like SQL injections and Cross-Site Scripting (XSS).

Codacy uses an early feedback system that alerts you as soon as it finds potential security risks in the code. As such, it helps your team write high-quality code that isn’t susceptible to security risks. Plus, Codacy integrates directly with your workflow, helping you save time.

Codacy Security helps explicitly you and your team understand your security posture:

  • Static Application Security Testing (SAST): Scrutinizes your source code to identify prevalent security vulnerabilities, such as those listed in the OWASP Top 10, including XSS (Cross-Site Scripting) and SQL injection, ensuring your code adheres to standard security best practices.
  • Supply Chain Security (SCA): Continuously scan your codebase to detect vulnerabilities and risks in open-source libraries you use, keeping track of known vulnerabilities and common vulnerabilities and exposures (CVEs).
  • Hard-Coded Secrets Detection (Secrets): Probes your code to uncover and alert you about any exposed sensitive information like API keys, passwords, certificates, and encryption keys, which are critical for maintaining data security.
  • Infrastructure-as-Code Configs (IaC): Analyzes Infrastructure-as-Code setups such as Terraform, CloudFormation, and Kubernetes, checking for misconfigurations and potential security issues in your infrastructure coding.

Automatically testing your code can also help find issues in code your team didn’t write, like third-party libraries and frameworks. They are great for saving time, and there is no need to reinvent the wheel when a library already exists. However, we still need to ensure no known vulnerabilities exist in our software's entire dependency tree.

To try out Codacy Quality and Security, sign up today for a free 14-day trial



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