Weakness · High
CWE-939: Improper Authorization in Handler for Custom URL Scheme
What it is
The product uses a handler for a custom URL scheme, but it does not properly restrict which actors can invoke the handler using the scheme.
- Severity (our rating)
- High
- Likelihood of exploit
- Not rated by MITRE
- Introduced during
- Implementation
- Exploited in the wild
- No CVE in CISA's catalog
In more detail
Mobile platforms and other architectures allow the use of custom URL schemes to facilitate communication between applications. In the case of iOS, this is the only method to do inter-application communication. The implementation is at the developer's discretion which may open security flaws in the application. An example could be potentially dangerous functionality such as modifying files through a custom URL scheme.
What an attacker can do
- Gain Privileges or Assume Identity (Access Control, Other)
- Varies by Context (Access Control, Other)
- Bypass Protection Mechanism (Access Control, Other)
How to prevent it
Architecture and Design
- Utilize a user prompt pop-up to authorize potentially harmful actions such as those modifying data or dealing with sensitive information. When designing functionality of actions in the URL scheme, consider whether the action should be accessible to all mobile applications, or if an allowlist of applications to interface with is appropriate.
How to find it
- Automated Static Analysis. Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
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Start freeSource: MITRE Common Weakness Enumeration, CWE version 4.19.1. CWE is a trademark of The MITRE Corporation.