CVE-2026-45531: fsck.c Privilege Escalation Vulnerability

CVE-2026-45531 Overview

CVE-2026-45531 is a heap-based buffer overflow in the read_boot_region function of fsck.c, a filesystem check utility component referenced in the Android Security Bulletin for September 2026. The flaw allows an out-of-bounds read from a heap buffer during boot region parsing. A local attacker with low privileges can leverage the condition to achieve local escalation of privilege. Exploitation requires no user interaction and no additional execution privileges. The weakness is categorized under [CWE-122] Heap-based Buffer Overflow.

Critical Impact
Local privilege escalation on affected Android systems through malformed filesystem structures parsed by fsck, with no user interaction required.

Affected Products

Android platform components referenced in the Android Security Bulletin September 2026
fsck filesystem check utility (fsck.c, function read_boot_region)
Devices consuming the vulnerable Android security patch level

Discovery Timeline

2026-09-08 - CVE-2026-45531 published to the National Vulnerability Database (NVD)
2026-09-10 - Record last modified in NVD

Technical Details for CVE-2026-45531

Vulnerability Analysis

The defect resides in read_boot_region inside fsck.c, part of the Android filesystem check tooling. During boot region parsing, the function reads past the bounds of a heap-allocated buffer. This out-of-bounds read exposes adjacent heap memory to attacker-influenced control flow. An attacker with local access can craft a filesystem image or block-level artifact that triggers the overread when fsck processes it. Successful exploitation results in escalation of privilege to the context in which fsck operates, which is typically elevated on Android devices. The attack executes without any user interaction, making automated exploitation practical on devices that auto-mount or auto-check attached storage.

Root Cause

The root cause is missing or insufficient bounds validation on length or offset fields consumed while parsing the boot region of a filesystem. The code trusts attacker-influenced metadata and reads beyond the size of the heap allocation. This class of defect is tracked as [CWE-122] Heap-based Buffer Overflow.

Attack Vector

Exploitation requires local access and low privileges. An attacker supplies a malformed filesystem structure that is subsequently processed by the vulnerable read_boot_region code path. Because user interaction is not required, the flaw can be chained with automated mount or repair operations to reach elevated execution context. Refer to the Android Security Bulletin September 2026 for platform-specific exploitation context.

Detection Methods for CVE-2026-45531

Indicators of Compromise

Unexpected invocations of fsck against attacker-controlled or newly attached storage devices
Crashes, segmentation faults, or abnormal termination logs originating from fsck on Android endpoints
Presence of malformed filesystem images or non-standard boot region metadata on managed devices

Detection Strategies

Monitor Android device logs for fsck errors, heap corruption traces, and kernel messages tied to filesystem parsing failures
Correlate elevation-of-privilege attempts with recent removable media or filesystem mount events
Track Android security patch level (SPL) across managed fleets and flag devices below the September 2026 baseline

Monitoring Recommendations

Alert on repeated fsck failures across a device fleet, which may indicate exploitation attempts
Audit privileged process spawns following storage attach or mount operations
Review mobile device management (MDM) telemetry for devices missing the September 2026 patch level

How to Mitigate CVE-2026-45531

Immediate Actions Required

Apply the Android security patch level dated 2026-09-01 or later, as published in the Android Security Bulletin September 2026
Inventory all Android devices and identify those running SPL earlier than 2026-09-01
Restrict local access on shared or kiosk-mode devices where fsck may be triggered against untrusted media

Patch Information

Google addressed the issue in the Android Security Bulletin for September 2026. Device manufacturers integrate the fix into vendor patch levels distributed through their update channels. Consult the Android Security Bulletin September 2026 for the authoritative list of affected components and patch identifiers.

Workarounds

Disable auto-mount and auto-repair for removable storage where operationally feasible
Enforce MDM policies that block untrusted USB or block-device attachment on production devices
Limit shell access to trusted administrators until patches are deployed

bash

# Verify Android security patch level on a managed device
adb shell getprop ro.build.version.security_patch

# Expected output should be 2026-09-01 or later