CVE-2026-21103: GalaxyDiagnostics Path Traversal Vulnerability

CVE-2026-21103 Overview

CVE-2026-21103 is a path traversal vulnerability [CWE-35] in the GalaxyDiagnostics component on Samsung mobile devices. The flaw exists in versions prior to the Samsung Mobile Release (SMR) Sep-2026 Release 1. An attacker with physical access to the device can traverse directory structures and read files that should be restricted to the system user. Because the diagnostic component runs with system privilege, successful exploitation exposes protected files stored under system-owned paths. The issue was addressed in the Samsung Mobile Security Maintenance Release for September 2026.

Critical Impact
Physical attackers can read files owned by the system user, exposing sensitive configuration data, credentials, and application state stored on the device.

Affected Products

Samsung Galaxy devices running GalaxyDiagnostics prior to SMR Sep-2026 Release 1
Samsung mobile firmware builds released before the September 2026 security patch level
Devices that have not yet installed the SMR Sep-2026 Release 1 update

Discovery Timeline

2026-09-09 - CVE-2026-21103 published to NVD
2026-09-10 - Last updated in NVD database
September 2026 - Samsung releases fix in SMR Sep-2026 Release 1

Technical Details for CVE-2026-21103

Vulnerability Analysis

The vulnerability resides in the GalaxyDiagnostics component, a preinstalled diagnostic application that runs with system-level privileges on Samsung mobile devices. GalaxyDiagnostics accepts a file path parameter without correctly canonicalizing or validating it against an allowlist of permitted directories. An attacker with physical access can supply path segments such as ../ to escape the intended working directory. The component then opens and returns the target file using its elevated system identity, bypassing standard Android sandbox boundaries between the user and system users.

Root Cause

The defect is classified as CWE-35: Path Traversal: .../...//. GalaxyDiagnostics resolves user-controllable input into a filesystem path without stripping traversal sequences before performing file operations. Missing canonicalization allows relative path components to reach the underlying open() call, which enforces Discretionary Access Control (DAC) based on the caller's UID rather than the request's origin.

Attack Vector

Exploitation requires physical proximity to the device, as reflected in the CVSS attack vector of Physical. The attacker interacts with the diagnostic interface directly on the device, supplying crafted input containing traversal sequences. No user interaction from the device owner is required, and no prior authentication is needed on the exposed diagnostic surface. Because GalaxyDiagnostics executes as system, files that would otherwise be unreadable to a normal user or app become accessible. Remote exploitation is not possible.

No public proof-of-concept exploit is available, and this vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. The EPSS score of 0.174% reflects a low modeled probability of exploitation in the near term. For technical details, refer to the Samsung Mobile Security Update.

Detection Methods for CVE-2026-21103

Indicators of Compromise

Unexpected access to system-owned files under /data/system/, /data/misc/, or vendor-specific diagnostic directories originating from the GalaxyDiagnostics process
Diagnostic log entries showing file path arguments containing ../ sequences or absolute paths outside the expected diagnostic scratch directory
Devices with a Samsung patch level prior to September 2026 that have been physically handled by untrusted parties

Detection Strategies

Audit mobile fleet inventory to identify Samsung devices reporting a build fingerprint older than SMR Sep-2026 Release 1
Review Mobile Device Management (MDM) telemetry for diagnostic app invocations and abnormal file read activity by system-privileged processes
Correlate physical custody events, such as repair or lost-and-found incidents, with subsequent anomalous account or credential activity

Monitoring Recommendations

Enforce MDM compliance policies that block or quarantine devices below the September 2026 Samsung patch level
Monitor enterprise identity providers for reuse of credentials or tokens that may have been stored on affected devices
Track diagnostic mode activation events through MDM logs and flag activations outside of authorized service workflows

How to Mitigate CVE-2026-21103

Immediate Actions Required

Install the Samsung SMR Sep-2026 Release 1 update on all affected Galaxy devices as soon as the carrier makes it available
Restrict physical access to corporate mobile devices and enforce screen lock, biometric, and strong PIN requirements
Disable or restrict access to diagnostic modes through MDM configuration profiles where supported

Patch Information

Samsung addressed the issue in the September 2026 Security Maintenance Release. Administrators should verify that the device security patch level reports September 1, 2026 or later. Update availability varies by device model and carrier. Refer to the Samsung Mobile Security Update bulletin for the full list of affected models and rollout status.

Workarounds

Keep devices in secure custody until the SMR Sep-2026 Release 1 patch is installed, since exploitation requires physical access
Enable full-disk encryption and require a strong screen lock so unauthorized users cannot reach the diagnostic interface
Use MDM policies to disable USB debugging and restrict boot into diagnostic or service menus on managed fleets

bash

# Verify Samsung security patch level via ADB on a managed test device
adb shell getprop ro.build.version.security_patch
# Expected output on a patched device: 2026-09-01 or later