Case UC-08 · OWASP M4 Insufficient Input/Output Validation

Deep link parameter passed unvalidated to a sensitive sink

A deep link handler passed unvalidated parameters into a web view and an internal router, so a crafted link could load hostile content or reach internal screens.

This article documents a representative, anonymised mobile application security case. It describes the weakness, why it matters to a business, how Mobexa detects it, and how to remediate it. No specific application, company or individual is identified.

Contents

  1. Context
  2. What the research team found
  3. Why it matters
  4. How Mobexa surfaces it
  5. Remediation
  6. Standards mapped

1 Context

An app registered a deep link and custom scheme whose parameters were passed, without validation, into a web view and an internal routing call. A crafted link could therefore steer the app to load attacker-chosen content or reach internal screens directly.

2 What the research team found

The team traced externally supplied link parameters into a web view load and a navigation sink with no allow-list or sanitisation. A link delivered by message, email or another app could carry values that the handler trusted and acted upon.

3 Why it matters

Unvalidated input from an external entry point is a classic foothold: it can load hostile pages inside the app's trusted context, bypass intended navigation, or pre-fill sensitive flows. The user only has to open a link for the handler to act.

4 How Mobexa surfaces it

Mobexa enumerates deep link and intent entry points, traces tainted parameters to sensitive sinks such as web views, file access and routing, and flags missing validation under M4.

5 Remediation

Validate and allow-list every externally supplied parameter, restrict web views to trusted origins, and never pass raw link input into navigation, file or query operations.

6 Standards mapped

Table 1. Frameworks and references for this case
FrameworkReference
OWASP Mobile Top 10 (2024) M4 Insufficient Input/Output Validation
CWE CWE-20 Improper Input Validation
OWASP MASVS MASVS-PLATFORM
input-validationdeep-linkwebview

See also

Documented by the Mobexa research team. This case is anonymised and provided for educational use; the mapping references the OWASP Mobile Top 10 (2024).