CVE-2026-45521: Android AppFuse Information Disclosure Flaw

CVE-2026-45521 is an information disclosure vulnerability in Android's AppFuseBridge.java due to missing permission checks. Attackers can access sensitive data locally without privileges or user interaction. This article covers technical details, affected versions, security impact, and mitigation strategies.

CVE-2026-45521 Overview

CVE-2026-45521 is a local information disclosure vulnerability in the openFile method of AppFuseBridge.java, a component of the Android operating system. The flaw stems from a missing permission check [CWE-693: Protection Mechanism Failure]. A local attacker with low privileges can read data they should not access, without user interaction and without gaining additional execution privileges. The issue was addressed in the Android Security Bulletin September 2026.

Critical Impact
A local, low-privileged process on an affected Android device can disclose information from files exposed through AppFuseBridge without triggering permission enforcement or user prompts.

Affected Products

Android operating system (AppFuseBridge component)
Devices covered by the Android Security Bulletin dated 2026-09-01
Refer to the vendor bulletin for the specific Android versions and patch levels

Discovery Timeline

2026-09-08 - CVE-2026-45521 published to the National Vulnerability Database (NVD)
2026-09-10 - Last updated in NVD database

Technical Details for CVE-2026-45521

Vulnerability Analysis

The vulnerability resides in the openFile method of AppFuseBridge.java, part of Android's AppFuse filesystem bridge. AppFuse mediates file access between applications and the Android storage subsystem using FUSE (Filesystem in Userspace). When openFile is invoked, the code path fails to enforce a required permission check before returning a file handle to the caller.

Because the check is absent, a local caller can obtain access to file content that the platform's permission model would otherwise restrict. Exploitation requires only local access and low privileges, and no user interaction is needed to trigger the disclosure. The scope is limited to information disclosure; the flaw does not grant write access or elevated execution privileges.

Root Cause

The root cause is a missing permission check inside openFile in AppFuseBridge.java. The Android permission model relies on explicit enforcement at security-relevant entry points. When such enforcement is omitted, callers bypass the protection mechanism entirely, which aligns with the classification under [CWE-693].

Attack Vector

An attacker delivers or runs a local, unprivileged application on the target device. That application invokes the affected openFile path in AppFuseBridge and receives access to file data it should not be permitted to read. The attack requires no privilege escalation, no additional exploit chain, and no user interaction. Technical details are documented in the Android Security Bulletin September 2026.

Detection Methods for CVE-2026-45521

Indicators of Compromise

Unexpected invocations of AppFuse-related IPC or openFile calls originating from non-system applications
Application processes reading file paths outside their declared storage scope
Installed applications requesting or exercising storage bridge functionality without a documented use case

Detection Strategies

Inventory installed applications and identify those interacting with AppFuse or scoped storage APIs beyond their expected behavior
Compare device Android security patch levels against the September 2026 bulletin to identify unpatched fleet devices
Review mobile threat defense telemetry for anomalous file access patterns tied to third-party apps

Monitoring Recommendations

Enroll Android devices in a mobile device management (MDM) solution and report on the ro.build.version.security_patch property
Alert when devices report a security patch level earlier than 2026-09-01
Monitor sideloaded application installations and privilege usage on corporate-managed Android endpoints

How to Mitigate CVE-2026-45521

Immediate Actions Required

Apply the Android security update dated 2026-09-01 or later on all affected devices
Confirm device patch level through MDM inventory reporting after update deployment
Restrict installation of untrusted or sideloaded applications on managed Android devices

Patch Information

Google published the fix as part of the Android Security Bulletin September 2026. Device manufacturers integrate the patch into their vendor images and distribute it through over-the-air updates. Administrators should track OEM release schedules to confirm the September 2026 patch level reaches all fleet devices.

Workarounds

No vendor-supplied workaround is documented; applying the security patch is the supported remediation
Reduce exposure by limiting installation to vetted applications from trusted sources such as Google Play
Enforce work profile separation to isolate corporate data from personal applications on shared devices

bash

# Verify the Android security patch level on a connected device
adb shell getprop ro.build.version.security_patch
# Expected output for a patched device: 2026-09-01 or later