What is Secure SDLC (SSDLC)? Integrating Cybersecurity into Your Software Development Lifecycle

A secure software development lifecycle strategy builds cybersecurity into program design instead of treating security as an add-on. Developers implement SSDLC by applying security best practices at each development lifecycle stage, from planning to maintenance. This helps ensure security and compliance while reducing the costs of fixing vulnerabilities.

In today's digital landscape, software security is paramount. Today we’ll provide a comprehensive overview of the Secure Software Development Lifecycle (SSDLC), a critical framework for building resilient and secure software. 

We'll explore the key components of SSDLC, its operational processes, and the significant benefits it offers. Additionally, we'll dive into best practices for implementation and guide where to find expert support.

SSDLC Defined: What Is Secure SDLC?

A secure software development lifecycle strategy (also known as development security operations or DevSecOps) enhances the traditional program design methodology by incorporating security into each process stage. This involves conducting risk assessments during the software planning and design phases and implementing vulnerability assessments after software development.

A secure SDLC approach departs from conventional SDLC methodologies that treat security as an add-on introduced late in the development lifecycle. With SSDLC, security goals guide development from the earliest stages and inform every phase of the application lifecycle.

A SSDLC approach can be applied to any type of application, from web and mobile apps to firmware. SSDLC serves all industries that prioritize software security, from big tech and data science to healthcare and finance.

SSDLC helps meet the needs of today's rapidly changing cybersecurity environment, where bad actors constantly strive to stay a step ahead of security teams. An SSDLC approach improves software providers' ability to maintain compliance as regulatory standards grow stricter to keep up with emerging threats.

Development and security teams achieve SSDLC by using frameworks such as the Open Worldwide Application Security Project (OWASP) or STRIDE to develop threat models. Teams then apply these models using methods and tools such as attack surface management (ASM), dynamic application security testing (DAST), static application security testing (SAST), software composition analysis (SCA), penetration testing (pentesting), and red teaming.

How Does SSDLC Work?

SSDLC applies security to each stage of the software development lifecycle, commonly divided into six stages:

1. Planning: defining project goals, requirements, schedule, and budget
2. Design: conceiving solutions to meet project requirements
3. Development: writing software code
4. Testing: checking code for quality and bugs
5. Deployment: releasing code into build and production environments
6. Maintenance: monitoring performance, fixing bugs, and making improvements

Here's how SSDLC integrates security into each of these stages:

1. Planning

As the earliest phase of the software development lifecycle, the planning stage represents the easiest, most efficient, and least expensive way to introduce security considerations into application design. Threat modeling is often helpful here to help lead the prioritization process for security teams. Based on project requirements, teams can set security goals aligned with brand objectives. For example, a team designing a fintech app can set data security and privacy goals consistent with regulatory requirements.

The planning phase should incorporate security into scheduling timetables and budgeting estimates. Adequate time should be allowed to include security testing in development deadlines. Budgets should factor in the cost of security tests.

2. Design

In the design phase, SSDLC focuses on developing a secure architecture. A comprehensive threat model approach encompasses all phases of emerging threats, from the time attackers begin gathering information on vulnerabilities to the manifestation of attacks in disruption of systems. 

Instead of focusing on the full cyberattack lifecycle, let's use the STRIDE model to categorize potential threats:

1. Spoofing: Impersonating another user or system. This could involve faking an email address, website, or user credentials.
2. Tampering: Modifying data or code. This could involve altering data in transit or changing a website's code to inject malicious scripts.
3. Repudiation: Denying that an action occurred. An attacker might try to cover their tracks by deleting logs or denying they sent a particular message.
4. Information Disclosure: Exposing sensitive information to unauthorized individuals. This could involve stealing customer data, accessing confidential company documents, or eavesdropping on network traffic.
5. Denial of Service: Disrupting or preventing legitimate users from accessing a system or service. This could be achieved by flooding a server with requests, exploiting a vulnerability to crash a system, or physically damaging infrastructure.
6. Elevation of Privilege: Gaining unauthorized access to resources or functionality. This could involve exploiting a vulnerability to gain administrator privileges or tricking a user into running malicious code.

To execute each of these attack phases, attackers deploy a variety of corresponding techniques. A complete security design should identify all potential attack surfaces and prioritize those deemed highest risk.

To prioritize risks, threat modeling should be followed up with risk assessment. Evaluating risks involves identifying which assets are vulnerable to cyberattack and how their exposure potentially impacts organizations and customers. This provides a basis for determining which risks represent the highest priorities for mitigation.

3. Development

As code is being written, developers can incorporate security by reviewing source code for vulnerabilities. Static application security testing tools can pinpoint bugs inherent in code before execution. SAST achieves this by parsing source code, building a syntax tree, and analyzing for a variety of vulnerabilities. Vulnerability analysis scans include checks for problems with configuration, semantics, dataflow, control flow, and structure. Checking for these kinds of issues early can save significant time and money later.

Note that static application security testing can't detect vulnerabilities that emerge during program execution, and SAST tests suffer from certain limitations. Notably, they're prone to false positives, especially when missing context. For instance, they may flag data sanitization vulnerabilities that don't actually emerge in live environments when applications are cleaning data input. To be used effectively, SAST tools must be customized to filter out false positives.

4. Testing

After the development phase and SAST testing, you can run tests in your build and production environments. This can help you identify vulnerabilities that appear during execution.

During this phase, DAST tools can help you assess risks stemming from runtime and environmental issues, such as server misconfigurations and API integrations. Software composition analysis tools can help you assess issues stemming from open-source components.

Penetration testing provides another invaluable tool for this phase. Pentesting simulates attacks on networks in order to identify vulnerabilities. It provides a comprehensive view of your app's vulnerabilities from an attacker's viewpoint, allowing you to spot risks that might go overlooked from a conventional security perspective.

5. Deployment

Once software has gone into deployment, security testing remains critical for intercepting real-time vulnerabilities as they emerge. Penetration testing continues to play a critical role, allowing you to conduct ongoing assessments of vulnerabilities. Red teaming also can be deployed to test your defenses against specific attacks.

6. Maintenance

A SSDLC approach requires continuous monitoring and mitigation during the maintenance phase of the software lifecycle. Continuous monitoring should track data from sources such as code reviews, support tickets, customer feedback, and threat updates. 

Furthermore, ASM is often used to detect unneeded or unused legacy assets should be decommissioned to reduce potential attack surfaces. ASM can help inform periodic pentests, which should be scheduled to verify the integrity of existing defenses. 

When vulnerabilities are detected, patches should be developed, implemented, and tested. New cybersecurity methods, tools, and threat intelligence should be integrated into security procedures.

Why Is SSDLC Important?

A SSDLC approach forms a critical part of effective cybersecurity for several key reasons:

• By taking security into account from the earliest stages of development and throughout the software lifecycle, SSDLC optimizes app integrity and minimizes vulnerabilities.
• By catching vulnerabilities early in the development lifecycle, SSDLC promotes a security shift left approach that reduces code rewriting and cuts costs
• By prioritizing security, SSDLC supports compliance with regulatory standards.

With respect to this last item, regulatory frameworks such as the EU Cyber Resilience Act now require an SSDLC approach. Additionally, some frameworks impose compliance requirements that include regular pentesting. For example, the payment industry's PCI-DSS standard requires pentesting at least once a year.

Six SSDLC Best Practices

SSDLC best practices aim to optimize security integration during the stages of the development lifecycle. Corresponding to the six stages of development outlined above, we can formulate the following best practice guidelines:

1. Define security goals from the onset of development
2. Use current threat model frameworks
3. Include static application security testing in your code review
4. Apply dynamic application security testing and software composition analysis during vulnerability assessment
5. Conduct penetration testing to probe vulnerabilities
6. Apply ongoing monitoring to promote continuous improvement

Here's a description of each best practice and tips for implementing it:

1. Define Security Goals from the Onset of Development

Your software planning stage should include explicit written identification of desired security outcomes. These should include: Information assurance goals for application and data confidentiality, integrity, availability, authenticity, and non-repudiation

• Compliance goals
• Security test scheduling tasks and timetables
• Security budgeting estimates

These goals should be developed in consultation with all relevant team members and stakeholders and codified in a written document available to all parties tasked with security. This document should be updated during development as the team identifies specific security issues.

2. Use Current Threat Model Frameworks

To model threats effectively, security teams should rely on current threat model frameworks that address the latest risks. One of today's most important threat model frameworks are:

• STRIDE, a classification system for identifying potential security threats 

• PASTA, a risk-centric threat modeling methodology that prioritizes and mitigates threats based on their likelihood and impact on business objectives.

Both frameworks offer invaluable tools for modeling threats and preparing mitigations. Depending on your needs, you may find one or both useful for customizing your own threat model.

That said, these frameworks include best practices such as least privilege and defense in depth. When paired with different parts of the SSDLC, they can become meaningful aspects of a security program.

3. Include Static Application Security Testing in Your Code Review

When conducting the security component of your code review, incorporate SAST testing into your procedures. Choose a SAST tool that supports your required programming languages and frameworks and integrates them into your development workflow. Adjust your configuration to flag the vulnerabilities you've prioritized and minimize false positives. 

At Cobalt, our secure code review service leverages SAST tools to enhance the efficiency and effectiveness of the security review process. This allows our team of security experts to quickly identify potential vulnerabilities and focus their expertise on more complex security issues that require manual analysis and remediation guidance. This combined approach ensures a thorough and efficient review, minimizing potential risks while maintaining development velocity.

4. Apply Dynamic Application Security Testing and Software Composition Analysis during Vulnerability Assessment

Dynamic application security testing and software composition analysis serve different functions in application vulnerability assessment, and both should be performed for a complete perspective. DAST tools help you analyze runtime communications between browsers and servers, which can help you catch problems such as server misconfigurations, authentication issues, and API integration problems.

SCA verifies third-party frameworks, libraries, and components. To do this, SCA relies on databases, vendor research, and information provided by component designers. Unlike SAST or DAST, SCA doesn't run static or dynamic analysis or review your own code, but focuses on third-party code. SCA tools cross-reference your app's dependency list against known vulnerabilities. In this way, SAST, DAST, and SCA complement each other and provide a more complete perspective on vulnerabilities.

5. Conduct Penetration Testing to Probe Vulnerabilities

Pentesting can be applied both during the testing and during the deployment phases of software development. It provides you with a comprehensive perspective on your application's vulnerabilities. This makes it strategic to perform pentesting before product release, immediately after product release, and any time there are major structural changes to your app, its ecosystem, or attacker tactics. Some regulatory frameworks require pentests to be performed annually.

6. Apply Ongoing Monitoring to Promote Continuous Improvement

Maintaining security measures pivots around establishing effective monitoring and response strategies and procedures. Your monitoring procedures should specify which items need to be tracked and leverage tools such as attack surface monitoring. 

Commonly tracked metrics within a continuous security program  include:

• Endpoints
• Security logs, events, and incidents
• User behavior patterns and changes
• Pentesting results
• Vulnerabilities
• Third-party vulnerabilities, fixes, and updates
• Threat intelligence
• Compliance controls

Monitoring procedures must be supplemented by threat response procedures. For example, ASM allows teams to continuously monitor their attack surface and its risk posture. This visibility allows security teams to discover previously unknown assets and ensure they aren’t left exposed to an attack.These include procedures for managing your patches and updates as well as those of third-party dependencies.

Regular pentest scheduling forms an important part of SSDLC continuous monitoring. At a minimum, pentests should be scheduled after product releases and updates as well as annually.

Secure Your Software Development Lifecycle to Reduce Risks and Ensure Compliance

With today's dynamic cybersecurity threats and strict regulatory climate, developers can no longer afford to treat security as a late add-on. Security considerations must be incorporated from the outset of the development process to minimize risks, ensure compliance, and protect brand reputation. Follow the best practices recommended in this blog to make sure security shapes your software throughout the development lifecycle.