• Platform: Android
• Weakness: MASWE-0027
• Weakness in the numbering of the MASWE beta: MASWE-0052
• Profiles: L1 (basic security), L2 (advanced security)
• Type: static, code, manual
• Knowledge: MASTG-KNOW-0010
• Best practices: MASTG-BEST-0021

Overview

This test evaluates whether an Android app uses checkServerTrusted(...) in an unsafe manner as part of a custom TrustManager, causing any connection configured to use that TrustManager to skip certificate validation.

Such unsafe implementations can allow an attacker to run a [MITM attack](../../../Document/0x04f-Testing-Network-Communication.md#intercepting-network-traffic-through-mitm) with a valid (or self-signed) certificate and intercept or tamper with the app's traffic.

Steps

1. Use MASTG-TECH-0013 to reverse engineer the app.
2. Use MASTG-TECH-0014 to look for the relevant APIs.

Observation

The output should contain a list of locations where checkServerTrusted(...) is used.

Evaluation

The test case fails if checkServerTrusted(...) is implemented in a custom X509TrustManager and does not properly validate server certificates.

Further Validation Required:

Inspect each reported code location using MASTG-TECH-0023, looking for cases such as:

• **Using checkServerTrusted(...) which is error prone, when NSC would be enough.
• Trust manager that does nothing: overriding checkServerTrusted(...) to accept all certificates without any validation, for example by returning immediately without verifying the certificate chain or by always returning true.
• Ignoring errors: failing to throw proper exceptions (e.g. CertificateException or IllegalArgumentException) on validation failure, or catching and suppressing them.
• Using checkValidity()) instead of full validation: relying only on checkValidity() checks whether the certificate is expired or not yet valid, but does not verify trust or hostname matching.
• Explicitly loosening trust: disabling trust checks to accept self-signed or untrusted certificates for convenience during development or testing.
• Misusing getAcceptedIssuers()): Returning null or an empty array without proper handling may effectively disable issuer validation.

Saincheisteanna nasctha

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