CVE-2026-28603 in Android
Summary
by MITRE • 09/08/2026
In assertSafeToStartCustomActivity of AppRestrictionsFragment.java, there is a possible read/write access to private files due to a confused deputy. This could lead to local escalation of privilege with no additional execution privileges needed. User interaction is not needed for exploitation.
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Analysis
by VulDB Data Team • 09/08/2026
The vulnerability identified in the assertSafeToStartCustomActivity method within AppRestrictionsFragment.java represents a critical security flaw rooted in a confused deputy scenario, which fundamentally compromises the integrity of file access controls on Android devices. This specific implementation error allows an attacker to manipulate the context or parameters passed during the execution of custom activities, thereby tricking the system into granting read and write permissions to files that are strictly designated as private to other applications or system components. In a typical secure architecture, each application operates within its own sandboxed environment with strict boundaries enforced by the operating system's permission model; however, this flaw bypasses those safeguards by exploiting the trust relationship between different app components when one component acts on behalf of another without adequately verifying the legitimacy of that request.
From a technical perspective, the core issue lies in the insufficient validation of input parameters and context before performing file operations. When assertSafeToStartCustomActivity is invoked, it fails to rigorously check whether the calling application has the appropriate authority to access the target private files. This lack of rigorous verification enables an unprivileged process to escalate its privileges locally by reading sensitive data or modifying critical configuration files that should remain immutable and inaccessible to unauthorized entities. The absence of required user interaction for exploitation significantly lowers the barrier for attackers, allowing them to execute this attack silently in the background without triggering any alerts or requiring explicit consent from the device owner.
The operational impact of this vulnerability is severe, as it facilitates local privilege escalation with no additional execution privileges needed beyond what a standard application possesses upon installation. An attacker who can install and run malicious code on the target device can leverage this flaw to exfiltrate sensitive user information such as credentials, personal messages, or financial data stored in private directories of other applications. Furthermore, the ability to write to these files allows for persistent compromise by altering system configurations or injecting malicious logic into trusted processes, effectively turning a standard app installation into a vector for deep system infiltration. This undermines the fundamental security model of Android, which relies on strict isolation between apps to prevent such cross-application data leakage and unauthorized modifications.
In terms of industry standards classification, this vulnerability aligns with CWE-269 Improper Privilege Management, specifically where an actor obtains privileges it should not have due to a failure in enforcing access control policies. It also maps closely to the Confused Deputy problem often associated with CWE-841 Improper Enforcement of Behavioral Workflow, as the system incorrectly assumes that because one component initiated a request on behalf of another, all subsequent actions are valid without further verification. From an offensive security standpoint, this technique is consistent with ATT&CK tactic T1055 Process Injection or T1074 Data Staged if used to prepare for broader attacks, but more directly relates to T1530 Data from Local System due to the direct access and exfiltration of private files.
Mitigation strategies must focus on hardening the permission checks within the AppRestrictionsFragment.java module. Developers should implement strict validation logic that verifies not only the identity of the calling process but also ensures that any file operations are explicitly authorized by the system's security manager based on current user permissions and app signatures. It is crucial to avoid relying solely on implicit trust relationships between components and instead enforce explicit allow-lists or deny-lists for file access paths. Additionally, applying principle of least privilege means ensuring that custom activities do not inherit broader permissions than necessary for their specific function. Regular code audits focusing on inter-process communication boundaries and dynamic permission checks are essential to prevent similar confused deputy vulnerabilities in future updates.