CWE-927: Use of Implicit Intent for Sensitive Communication

How it's found

Use of Implicit Intent for Sensitive Communication is a specific, narrowly defined instance of a broader pattern. Testers confirm it with targeted code review and a proof-of-concept input that exercises the exact code path this weakness describes.

Since an implicit intent does not specify a particular application to receive the data, any application can process the intent by using an Intent Filter for that intent. This can allow untrusted applications to obtain sensitive data. There are two variations on the standard broadcast intent, ordered and sticky. Ordered broadcast intents are delivered to a series of registered receivers in order of priority as declared by the Receivers. A malicious receiver can give itself a high priority and cause a denial of service by stopping the broadcast from propagating further down the chain. There is also the possibility of malicious data modification, as a receiver may also alter the data within the Intent before passing it on to the next receiver. The downstream components have no way of asserting that the data has not been altered earlier in the chain. Sticky broadcast intents remain accessible after the initial broadcast. An old sticky intent will be broadcast again to any new receivers that register for it in the future, greatly increasing the chances of information exposure over time. Also, sticky broadcasts cannot be protected by permissions that may apply to other kinds of intents. In addition, any broadcast intent may include a URI that references data that the receiving component does not normally have the privileges to access. The sender of the intent can include special privileges that grant the receiver read or write access to the specific URI included in the intent. A malicious receiver that intercepts this intent will also gain those privileges and be able to read or write the resource at the specified URI.

Consequences

• Read Application Data: Other applications, possibly untrusted, can read the data that is offered through the Intent.
• Varies by Context: The application may handle responses from untrusted applications on the device, which could cause it to perform unexpected or unauthorized actions.

Mitigations

• Implementation: If the application only requires communication with its own components, then the destination is always known, and an explicit intent could be used.

Where this fits in a TurboPentest engagement

This weakness is not covered by the automated black-box pentest. IntegSec pentesters cover it in a manual engagement.

Frequently asked questions

Related CWEs

• Class weakness
  CWE-285: Improper Authorization
• Class weakness
  CWE-668: Exposure of Resource to Wrong Sphere