Issue Details
Unvalidated Input
Aliases: None
Explanation
In OWASP 2003, A1 Unvalidated Input combines related risk themes across Injection, Cross-Site Scripting (XSS), Input Validation. Injection vulnerabilities happen when untrusted input is interpreted as code, queries, or commands. XSS lets attacker-controlled scripts execute in a victim's browser by injecting untrusted content into pages. Input validation flaws allow unexpected or malicious data to bypass business and security constraints. These weaknesses are often exploited as a chain: attackers start with weak input or trust boundaries, pivot through authorization or session gaps, and then move toward data exposure, integrity loss, or service disruption. Operationally, this can increase incident frequency, enlarge blast radius, and raise both remediation cost and compliance exposure when controls are missing or inconsistently enforced across services.
Remedy
For OWASP 2003 A1 Unvalidated Input, apply defense in depth across design, implementation, deployment, and operations rather than relying on a single control. Priority controls include: Use parameterized queries, output encoding, strict input validation, and avoid dynamic command/query concatenation. Apply contextual output encoding, sanitize HTML input, enforce CSP, and avoid unsafe DOM APIs. Validate and normalize input with allowlists by type, format, and range before business logic processing. Treat mitigation as a continuous program: define security requirements up front, enforce them in CI/CD gates, and verify effectiveness with threat modeling, code review, automated testing, and recurring penetration testing. Add monitoring and incident-response readiness so misconfigurations, abuse patterns, and control regressions are detected early and corrected before they become repeatable attack paths.
| Year | Rank | Category |
|---|---|---|
| 2003 | #1 | A1 - Unvalidated Input |
| 2003 | #4 | A4 - Cross-Site Scripting (XSS) |
| 2004 | #1 | A1 - Unvalidated Input |
| 2004 | #4 | A4 - Cross-Site Scripting (XSS) |
| 2007 | #1 | A1 - Cross Site Scripting (XSS) |
| 2007 | #2 | A2 - Injection Flaws |
| 2010 | #1 | A1 - Injection |
| 2010 | #2 | A2 - Cross-Site Scripting (XSS) |
| 2017 | #1 | A1 - Injection |
| 2017 | #7 | A7 - Cross-Site Scripting (XSS) |
| 2021 | #3 | A03 - Injection |
| 2025 | #5 | A05 - Injection |