As a cybersecurity analyst specializing in Static Application Security Testing (SAST), I spend a lot of my time analyzing application source code for security weaknesses before the software is deployed. While automated scanners are powerful, there's something unmatched about manual source code review the human eye can catch subtle issues that tools sometimes miss.

Recently, during a review for one of our client applications, I came across three critical security flaws that could have been exploited by attackers if left unpatched: hardcoded credentials, path traversal, and log forgery.

Why Manual Review Still Matters in SAST

Automated tools can quickly scan thousands of lines of code, flagging obvious patterns and known vulnerabilities. However, they:

  • Often produce false positives or miss context-specific issues.
  • Cannot always understand business logic flaws.
  • Fail to detect certain vulnerabilities that require code flow understanding.

That's where manual review comes in.

It allows you to:

  • Trace variable flow.
  • Understand developer intentions.
  • Detect hidden logic bombs and risky coding practices.

The Vulnerabilities I Found

1. Hardcoded Credentials : While reviewing a configuration file, I noticed something unusual: String dbUser = "admin"; String dbPassword = "P@ssw0rd123";

This is a textbook example of hardcoded credentials – a direct violation of secure coding practices.

Risks:

  • Anyone with access to the repository could retrieve these credentials.
  • If committed to a public repo, credentials could be harvested by attackers.
  • Hard to rotate and update credentials without redeploying code.

Recommendation: Store credentials in environment variables or secure vaults such as AWS Secrets Manager, HashiCorp Vault, or Azure Key Vault.

2. Path Traversal

In a file upload handler, I found this snippet:

String fileName = request.getParameter("file");

File file = new File("/var/app/uploads/" + fileName);

Here, user input is directly concatenated into a file path.

If an attacker sends:

../../../../etc/passwd

The code would attempt to read sensitive system files.

Recommendation:

  • Validate and sanitize file paths.
  • Restrict file access to allowed directories.
  • Use libraries like java.nio.file.Paths with proper normalization checks.

3. Log Forgery

In the logging mechanism:

logger.info("User action: " + request.getParameter("action"));

The action parameter comes directly from user input. An attacker could insert malicious log entries: action=%0a[CRITICAL] User admin deleted all data

This could pollute log files, mislead forensic analysis, or hide real attacks.

Recommendation:

  • Sanitize log input.
  • Encode special characters before writing to logs.
  • Avoid directly logging user input without context.

Lessons Learned

1. Security is a mindset – Automated SAST tools are great, but manual review finds issues they miss.

2. Think like an attacker – Trace the code as if you were exploiting it.

3. Document findings clearly – Developers fix issues faster when vulnerabilities are explained with risk and remediation steps.

Final Thoughts

Manual SAST review is not about replacing automation but complementing it. By combining the speed of automated tools with the precision of human review, we can build software that's not only functional but also secure. In my case, finding these vulnerabilities before deployment saved the client from potential data breaches, regulatory fines, and reputational damage.

💬 Have you ever found a hidden vulnerability during manual review? Share your experience in the comments the more we learn from each other, the stronger our defenses become.