# What Is Source Code Analysis? A Guide to SAST and Code Security

**URL:** https://securesys.com.tr/en/learning/source-code-analysis/what-is-source-code-analysis-sast-guide

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Modern software is no longer just a set of tools supporting an organisation's operations; from financial transactions to customer data, from production systems to critical business processes, it forms the foundation of the digital world. As web applications, mobile applications, API services, microservice architectures and cloud-based systems evolve, the source code behind those applications becomes one of an organisation's most critical assets.

The user-facing side of an application may look secure. Servers may be up to date, firewalls may be correctly configured, and the application may pass externally conducted security tests successfully. Yet a single missing check in the application's source code, a faulty authorisation mechanism or an insecure data-handling function can cause every one of those security layers to be bypassed.

Because the starting point of many vulnerabilities is not the infrastructure — it is the **code**.

For this reason, modern application security does not regard testing only the running application as sufficient. Security must be addressed as early as possible in the software development life cycle, and the source code must be examined from a security perspective.

This is where **Source Code Analysis** and **SAST – Static Application Security Testing** come in.

Source code analysis is the process of examining an application's source code for vulnerabilities, insecure programming practices, faulty data flows, authentication and authorisation problems, sensitive data usage, cryptographic errors and other software security risks.

But modern source code security means far more than that.

The goal is not merely to find errors in the code.

The real goal is:

**detecting vulnerabilities before they reach production, guiding developers correctly, and making a secure software development culture part of the organisation's software life cycle.**

### \1. What Is Source Code Analysis?

Source code analysis is the systematic examination, from a security perspective, of the programming code an application is built from.

This examination can be carried out with automated security tools, manually by security specialists, or by using both approaches together.

The aim is to detect as early as possible the vulnerabilities an attacker could use within the code that makes the application work.

For example, if data taken from a user in a web application is passed directly into a database query without any validation, that can lead to SQL Injection risk.

Similarly, many security problems can arise directly at source code level, such as:

- user input not being validated,
- missing authorisation checks,
- sensitive information kept inside source code,
- API keys hard-coded in plain text,
- use of insecure cryptographic algorithms,
- file operations performed without control,
- user input passed into operating system commands,
- error messages exposing sensitive system information.

Source code analysis makes it possible to detect these problems before the application is attacked.

Source code analysis is therefore not merely a security test but also a **proactive software security approach.**

### \2. Why Does Code Security Matter So Much?

An application's security consists of many different layers.

Security technologies such as firewalls, WAF, EDR, IPS and SIEM play an important role in protecting systems.

But most of these technologies cannot fully understand the business logic inside the application itself.

For example, when a user should only be able to view their own invoices but can view other customers' invoices by changing a parameter in the URL, that is a **Broken Access Control** problem.

Network security devices may see this action as an ordinary HTTPS request.

From the firewall's point of view the connection is entirely normal.

From the WAF's point of view the HTTP request may contain no malicious payload.

Yet the authorisation check in the application's source code is missing.

This is exactly where code security becomes important.

An attacker can bypass security mechanisms by using the application's own behaviour.

So in a modern security approach the question is not only:

**"Can our system be attacked?"**

It is also necessary to answer:

**"Has our software been developed securely?"**

### \3. Where Do Vulnerabilities Begin?

A vulnerability usually appears long before the application reaches production.

A developer may write a few lines of code while building a new feature.

Technically, that code may do its job correctly.

But its security checks may be missing.

Consider, for example, a value taken from the user being added directly into an SQL query.

The function will work.

The user will be able to search.

The database will return results.

Functional tests may pass successfully.

Yet when the same function is manipulated by an attacker it can turn into an SQL Injection vulnerability.

A similar situation can occur in a file upload feature.

A function allowing users to upload a profile photo may be developed.

But if the file type, content structure, MIME type, extension and the directory the file is saved to are not checked properly, an attacker may upload a malicious file to the server.

The important point here is this:

**Code may work and still not be secure.**

This is one of the fundamental problems of software security.

Functional correctness and security are not the same thing.

### \4. What Is SAST?

SAST — **Static Application Security Testing** — is a static application security testing approach that analyses source code or related software components for security without running the application.

SAST tools analyse particular code structures, data flows and security-risky usage patterns within source code.

SAST is therefore often regarded as the automation layer of source code analysis processes.

SAST systems try to analyse:

- where user input comes from,
- how that input is processed within the application,
- which functions it is passed to,
- whether validation or filtering is applied,
- whether it reaches risky functions.

For example, if a parameter coming from the user is found to reach an SQL query without passing through any security check, the system may raise a potential SQL Injection finding.

Likewise, passing user-controlled data into an operating system command may be assessed as a Command Injection risk.

One of SAST's most important advantages is that it moves security analysis into the early stages of the software development process.

### \5. Are Source Code Analysis and SAST the Same Thing?

These two concepts are often used interchangeably, but they are not identical.

**SAST** is one of the important automated components of source code security analysis.

**Source code analysis** is a broader security assessment.

A comprehensive source code security analysis can include manual security reviews alongside automated SAST scans.

This distinction matters especially in complex applications.

Because it is not possible for automated tools to detect every security problem.

For example, an authorisation problem tied to the application's business logic may not be understood by looking at code patterns alone.

Consider a banking application with a business rule such as:

"A standard user may transfer a maximum of 100,000 TRY per day."

Technically, the code may work entirely correctly.

But if that check has been forgotten on a particular API endpoint, an attacker may exceed the limit by using a different transaction flow.

The SAST tool may consider the functions used to be safe.

An experienced security specialist, however, can detect the problem by examining the application's business logic and data flow.

A strong source code analysis approach must therefore consider these components together:

**Automated Analysis + Manual Security Review + Finding Validation**

### \6. How Does Source Code Analysis Work?

The first stage of source code analysis is understanding the application's technical structure.

Which programming language is used?

Which frameworks are present?

What is the application's architecture?

Which services does it communicate with?

How is authentication performed?

Where is data stored?

Which third-party libraries are used?

These questions form the basis of the security analysis.

Next, the application's attack surface is assessed.

User-controlled input in particular, and the critical functions that input reaches, are examined.

In modern static analysis systems this process is mostly carried out with techniques such as **source-to-sink analysis** and **taint analysis**.

#### Source

The point at which data controllable by a user or external system enters the application.

For example:

HTTP parameters, form fields, API request bodies, HTTP header information, cookie values or file uploads can be regarded as sources.

#### Sink

The point at which data reaches a function that is critical from a security perspective.

For example:

SQL queries, operating system commands, file system functions, HTML output or network calls can be sinks.

#### Sanitization

The validation or cleaning operations applied to make user input safe.

During analysis the system essentially asks this question:

#### Can user-controlled data reach a critical function without being made safe?

If the answer is yes, a potential vulnerability exists.

### \7. Which Vulnerabilities Can Source Code Analysis Find?

Source code analysis can be used to detect a very wide range of security problems.

Injection vulnerabilities come first among them.

#### SQL Injection

SQL Injection occurs when user-controlled data is included in SQL queries in an insecure way.

A successful attack can allow an attacker to access information in the database, modify data, or in some cases carry out further attacks on the system.

During source code analysis, how SQL queries are constructed and how user input is passed into them is examined.

#### Cross-Site Scripting – XSS

XSS vulnerabilities can occur when user input is passed to a web page without being safely encoded.

Source code analysis can identify potential XSS points by examining how user-controlled data is passed into HTML or JavaScript context.

#### Command Injection

Using user input in operating system commands can create serious security risks.

Successful Command Injection attacks can in some cases progress as far as the attacker executing commands on the server.

#### Path Traversal

Building file paths using user input can allow an attacker to access files outside the permitted directories.

#### Server-Side Request Forgery – SSRF

When URLs or addresses controlled by the user are called directly by the server, an attacker may reach internal systems the application can access.

In cloud environments in particular, SSRF vulnerabilities can have serious security consequences.

#### Insecure Deserialization

Deserializing untrusted data without control can, in some technologies, lead to serious consequences such as code execution or manipulation of application logic.

#### Broken Access Control

Missing or incorrectly applied authorisation checks can allow users to reach data or functions they should not access.

This category is one of the most critical risk areas in modern web applications.

### \8. API Keys and Passwords Inside Source Code

Code security does not consist only of classic application vulnerabilities.

One of the significant risks in modern software development is **secret exposure** — keeping confidential information inside source code.

During testing or integration, developers may accidentally add critical data into source code, such as:

- API keys,
- database passwords,
- access tokens,
- cloud credentials,
- private key material,
- service accounts,
- connection details.

Once that code is pushed to a repository system such as Git, the password may remain in past commits even if it is deleted later.

For this reason **Secret Scanning** has become an important control in modern code security programmes.

The aim is to assess not only the current source code but also the repository history from a security perspective.

Sensitive information should be kept outside source code wherever possible, and central secret management systems should be used.

### \9. Third-Party Libraries Are Part of Code Security Too

Developers do not write the whole of a modern software project from scratch.

Applications may consist of hundreds or even thousands of open source and third-party components.

This gives rise to a new security domain:

**Software Supply Chain Security.**

Even when the code written by the developer is secure, a critical vulnerability may exist in a library being used.

Analysing only the source code written by the developer is therefore not enough.

The application's dependencies must be analysed as well.

This process is called **Software Composition Analysis – SCA**.

SCA systems identify the packages and versions in use and try to correlate them with known vulnerabilities.

In addition, the use of **SBOM – Software Bill of Materials** is becoming steadily more important in modern security programmes.

An SBOM aims to set out an inventory of the components contained within a piece of software.

That way, when a new vulnerability is published, organisations can determine more quickly which of their applications use the affected component.

### \10. What Is the Difference Between Source Code Analysis and Pentest?

Source code analysis and penetration testing are not alternatives to one another.

On the contrary, they are two complementary security approaches.

In a penetration test the security specialist largely assesses the application from an attacker's perspective.

Requests sent to the application, APIs, session mechanisms, authorisation checks and other attack surfaces are tested.

In source code analysis, by contrast, the application's internal structure is visible.

Some security problems can therefore be detected far more easily at source code level.

For example, a hard-coded API key in the code may never become visible during an externally conducted pentest.

Conversely, some business logic flaws can be uncovered more easily in attack simulations performed against the running application.

A strong Application Security programme should therefore use these approaches together according to risk level:

**SAST + SCA + DAST + Manual Code Analysis + Pentest**

### \11. What Is Shift Left Security?

In traditional software development models, security testing was mostly carried out in the final stage of a project.

The application is developed.

It is moved to a test environment.

Functional tests are completed.

Then it is sent to the security team.

When a critical security problem is detected at this stage, fixing it can be difficult.

Because the code is finished, the architecture is settled and the application is close to production.

The modern approach aims to move security as far towards the beginning of the development process as possible.

This approach is called **Shift Left Security**.

The basic idea is simple:

**The earlier you detect a vulnerability, the easier it is to fix.**

For example, an automated SAST check can run the moment a developer pushes code to the repository.

If a critical security problem is found, the developer can be warned while still working on that code.

This approach does not aim to make the security team an obstacle in front of development teams, but to integrate security naturally into the software development process.

### \12. What Is Secure SDLC?

Secure Software Development Life Cycle — **Secure SDLC** — means integrating security controls into the whole of the software development life cycle.

Security does not begin only at the testing stage.

It is addressed from the planning stage onwards.

For example, within a secure software development life cycle there can be different security controls at every one of these stages:

**Planning → Design → Development → Code Analysis → Build → Test → Security Testing → Deployment → Monitoring**

Threat modelling can be performed at the design stage.

Secure Coding standards can be applied during development.

Secret scanning can run at commit time.

SAST and SCA checks can be performed during the build.

DAST can be applied in the test environment.

A manual penetration test can be carried out before release.

In the production environment, logging, monitoring and incident response mechanisms come into play.

This structure turns security from a one-off test into a continuous process.

### \13. Why Does CWE Matter in Source Code Analysis?

Classifying the errors encountered in code security using a common language is important.

Here, **CWE – Common Weakness Enumeration** is an important reference model.

CWE helps classify the fundamental weakness types of software security problems rather than a vulnerability in a specific product.

For example, mapping a security finding to the relevant CWE category rather than reporting it merely as an "injection problem" provides more standardised security management.

This approach matters especially in large software teams.

Because the organisation can analyse which security errors recur over time.

If analyses repeatedly surface the same authorisation problem, for instance, the issue is not a vulnerability in a single application.

There may be a systematic gap in the development standard or in developer training.

Source code analysis can therefore be used not only to find vulnerabilities but also **to measure software security maturity.**

### \14. OWASP and Source Code Security

When it comes to web application security, OWASP is one of the most important references.

The security guides published by OWASP are widely used by application security teams and developers.

But it is not right to see source code analysis merely as an OWASP Top 10 check.

The OWASP Top 10 is a strong starting point for understanding important risk categories.

At enterprise level, more detailed security requirements are needed.

Here, structures such as **OWASP ASVS – Application Security Verification Standard** can be used.

ASVS helps assess the security controls an application should contain in a more systematic way.

Considering OWASP, CWE and the organisation's own Secure Coding standards together during source code analysis creates a stronger security model.

### \15. Which Programming Languages Can Source Code Analysis Be Performed In?

Source code security analysis can be carried out for a large number of modern programming languages and frameworks.

For example:

- Java
- C#
- JavaScript
- TypeScript
- Python
- PHP
- C
- C++
- Go
- Kotlin
- Swift

Static security analysis can be performed on languages such as these.

But the analysis methods used can differ according to the programming language.

Understanding the framework structure also matters.

For example, the security controls of a Java application using Spring Boot and a PHP application using Laravel are not assessed in the same way.

Source code analysis should therefore not be seen merely as running a scanning tool.

**Programming language + framework + architecture + data flow + business logic**

must be assessed together.

### \16. Is Automated Source Code Analysis Enough?

Automated security tools are extremely valuable in that they can analyse very large code bases in a short time.

But they are not sufficient on their own.

One of the main reasons is the **false positive** problem.

A SAST system may detect a potential security problem, yet the finding may not actually be exploitable because of a control implemented in a different layer of the application.

The opposite is also possible.

The tool may fail to notice a security problem.

That situation can be assessed as a **false negative**.

Manual review becomes important particularly for business logic, complex authorisation models and application-specific security controls.

In a professional source code analysis approach, tool output must therefore be validated by security specialists.

The aim is not to hand the customer thousands of lines of automated tool output.

The aim is:

**to surface the real risks.**

### \17. When Should Source Code Analysis Be Performed?

Treating source code analysis as a control to be performed only once a year is not sufficient for modern software development processes.

In projects under continuous development in particular, code can change every day.

New functions are added.

New APIs are created.

New libraries are added.

Security analysis should therefore be made as continuous as possible.

For example:

The developer can receive security warnings at IDE level while writing code.

Secret scanning can be performed at commit time.

SAST can run during a merge request.

SCA checks can be performed during the build.

Manual source code analysis can be carried out at particular release periods.

A pentest can be performed before critical releases.

This model takes security beyond being a one-off project.

### \18. What Should a Source Code Analysis Report Contain?

A professional source code analysis report should not consist merely of a list of the vulnerabilities found.

Every finding must be understandable and fixable by the developer.

A well-prepared source code security report should contain at least the following:

- The name of the finding
- Risk level
- Affected code or component
- Technical explanation
- Root cause of the vulnerability
- Possible attack scenario
- Business impact
- CWE mapping
- CVSS assessment where required
- OWASP relationship
- Secure coding recommendation
- Remediation steps
- Retest result

The important point here is establishing a common language between the security team and the developer.

Telling the developer only:

**"This code is insecure."**

is not enough.

Why it is insecure and how it should be fixed must be explained.

### \19. What Does Source Code Analysis Give Organisations?

Source code analysis is not used only to reduce the number of vulnerabilities.

Applied correctly, it also raises the quality of the organisation's software development.

One of the most important gains is early detection of security problems.

Fixing a critical vulnerability in an application already in production may require emergency response, operational downtime, a new release and extensive testing.

The same problem can be fixed far more easily when detected while the developer is writing the code.

In addition, recurring security problems can be analysed to create Secure Coding training tailored to development teams.

If an organisation's applications repeatedly show Broken Access Control problems, for example, training and development standards can be focused specifically on authorisation architecture.

The security organisation thereby stops being reactive.

**It turns into a measurable, improvable and sustainable software security programme.**

### \20. From Source Code Analysis to an Enterprise Code Security Programme

The most important point of the source code analysis journey begins here.

In the first stage an organisation may have the source code of a single application analysed.

In the second stage SAST systems can start being used.

SCA and Secret Scanning can then be added.

In the next stage these technologies are integrated into CI/CD processes.

Secure Coding training is then delivered to development teams.

Manual code analysis and regular pentest processes are established for critical applications.

In the final stage all of these controls are managed within a central **Application Security Programme**.

The maturity journey can be thought of as follows:

**Pentest → Source Code Analysis → SAST → SCA → Secret Scanning → DevSecOps → Secure SDLC → Application Security Programme**

This approach enables an organisation not only to find vulnerabilities but to develop its capacity to produce secure software.

### The SecureSys Approach to Source Code Analysis and Code Security

At SecureSys we do not regard source code security as consisting solely of the results produced by an automated SAST tool.

In our source code analysis approach, the application's technology stack, architecture, data flows, authentication and authorisation mechanisms, third-party components and critical business functions are assessed together.

Depending on the need and the project scope:

#### SAST, manual source code analysis, SCA, Secret Scanning, DAST, API security testing and penetration testing

can be addressed together.

Reporting the security findings is not the whole of it: development teams being able to understand and safely fix those findings is an important part of the process too.

Our aim is not only to find existing vulnerabilities.

**The aim is to establish a sustainable code security approach that prevents the vulnerability from recurring in the next software release.**

### Frequently Asked Questions

#### What is source code analysis?

Source code analysis is the examination of a piece of software's source code for vulnerabilities and insecure coding practices. Automated SAST tools and manual security analysis can be used together.

#### What is SAST?

SAST is short for Static Application Security Testing. It enables source code or related software components to be analysed statically for security without running the application.

#### Are source code analysis and SAST the same thing?

Not exactly. SAST is one of the important methods on the automation side of source code analysis. Comprehensive source code analysis can also include manual security review, business logic analysis and finding validation.

#### What is the difference between source code analysis and pentest?

A pentest assesses the running application from an attacker's perspective, while source code analysis examines the application's internal code structure. The two approaches are complementary, not alternatives.

#### Which vulnerabilities can source code analysis find?

SQL Injection, XSS, Command Injection, SSRF, Path Traversal, insecure deserialization, authorisation problems, hard-coded credentials, cryptographic errors and many other software security problems.

#### Is SAST enough on its own?

No. Automated analysis systems are very valuable but can produce false positives and false negatives. For business logic and complex authorisation problems in particular, complementary methods such as expert review and pentesting are needed.

#### How often should source code analysis be performed?

In continuously developed applications, integrating security controls into CI/CD processes is recommended. Alongside that, manual security assessments can be carried out after critical releases and major changes.

### Conclusion: Secure Software Begins with the First Line of Code

For many years cybersecurity focused largely on protecting systems from the outside.

Firewalls were installed.

IDS and IPS systems were deployed.

WAF technologies were used.

SOC centres were established.

But as software moved to the centre of the digital world, the point at which security begins changed too.

Today the critical question is not only whether systems are protected against attacks.

One of the real questions is this:

#### Is the software that makes up these systems secure?

Source code analysis is one of the most important ways of answering that question.

But real code security is far broader than running a SAST scan.

Secure software development requires these approaches to work together:

#### Secure Coding, SAST, SCA, Secret Scanning, manual source code analysis, DevSecOps, penetration testing and Secure SDLC

Because security does not begin in the production environment.

**Security begins with the first line of code.**