CVE-2021-25337: Samsung Android Auth Bypass Vulnerability

CVE-2021-25337 Overview

CVE-2021-25337 is an improper access control vulnerability affecting the clipboard service in Samsung mobile devices running Android. This flaw allows untrusted applications to read or write certain local files on the device, bypassing intended security restrictions. The vulnerability exists in Samsung Android devices prior to the SMR Mar-2021 Release 1 security patch.

This vulnerability has been actively exploited in the wild and is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, making it a significant concern for enterprise mobile security teams and individual users of Samsung devices.

Critical Impact

This vulnerability enables untrusted applications to access sensitive local files through the clipboard service, potentially leading to data theft, privacy breaches, and further exploitation of the device.

Affected Products

• Samsung Android 9.0 (all SMR releases prior to Mar-2021)
• Samsung Android 10.0 (all SMR releases prior to Mar-2021)
• Samsung Android 11.0 (SMR releases through Feb-2021)

Discovery Timeline

• March 4, 2021 - CVE-2021-25337 published to NVD
• October 30, 2025 - Last updated in NVD database

Technical Details for CVE-2021-25337

Vulnerability Analysis

The vulnerability resides in Samsung's proprietary clipboard service implementation on Android devices. The clipboard service, which handles copy-paste operations across applications, contains improper access control mechanisms that fail to properly validate application permissions before allowing file operations.

The attack requires local access, meaning a malicious application must be installed on the device. However, once installed, the malicious app can leverage the clipboard service's elevated privileges to read or write files that should be protected from untrusted applications. This creates a significant security gap as users may inadvertently install seemingly benign applications that exploit this vulnerability.

The impact is substantial as successful exploitation can result in unauthorized access to sensitive user data stored on the device (confidentiality breach) and modification of system or application files (integrity breach). This vulnerability is classified under CWE-269 (Improper Privilege Management).

Root Cause

The root cause of this vulnerability is improper access control implementation in Samsung's clipboard service. The service fails to properly enforce permission boundaries when handling file operations, allowing untrusted applications to perform privileged file read and write operations through the clipboard interface. The clipboard service runs with elevated privileges to function across applications, but lacks proper validation of the calling application's authorization to access specific files.

Attack Vector

The attack is local in nature, requiring user interaction to install a malicious application. Once the malicious application is running on the device, it can:

1. Interface with the clipboard service using standard Android IPC mechanisms
2. Request file operations through the clipboard service without proper authentication
3. Read sensitive files such as configuration data, cached credentials, or private user content
4. Write to protected file locations, potentially modifying system behavior or planting malicious payloads

Since the vulnerability requires local access and user interaction (installing a malicious app), social engineering tactics may be employed to trick users into installing malicious applications disguised as legitimate software.

The vulnerability mechanism exploits the clipboard service's privileged access to the file system. When an untrusted application interacts with the clipboard service, insufficient access control checks allow the application to specify file paths for read or write operations that the clipboard service executes with its elevated privileges. This effectively bypasses Android's application sandboxing model.

Detection Methods for CVE-2021-25337

Indicators of Compromise

• Unexpected file access patterns from clipboard-related processes or services
• Applications requesting unusual clipboard permissions or making frequent clipboard API calls
• Modification of system files or protected storage areas by non-system applications
• Suspicious inter-process communication involving the clipboard service

Detection Strategies

• Monitor application behavior for excessive clipboard service interactions, particularly those involving file operations
• Implement mobile threat defense solutions that detect applications exhibiting privilege escalation behaviors
• Review installed applications for known malicious packages that exploit this vulnerability
• Audit device logs for clipboard service errors or unusual file access requests

Monitoring Recommendations

• Deploy mobile device management (MDM) solutions to enforce application whitelisting policies
• Enable detailed logging on managed devices to capture clipboard service activity
• Implement behavioral analysis tools that can detect anomalous file access patterns
• Regularly scan devices for applications that may exploit known Samsung vulnerabilities

How to Mitigate CVE-2021-25337

Immediate Actions Required

• Update all Samsung mobile devices to SMR Mar-2021 Release 1 or later immediately
• Review and remove any suspicious or unnecessary applications from affected devices
• Enable Samsung Knox security features if available on enterprise-managed devices
• Restrict application installation to trusted sources only (Google Play Store, Samsung Galaxy Store)

Patch Information

Samsung has addressed this vulnerability in the SMR Mar-2021 Release 1 security update. The patch corrects the improper access control implementation in the clipboard service by adding proper permission validation for file operations. Device administrators and users should verify their security patch level through Settings > About Phone > Software Information > Android Security Patch Level.

For detailed patch information, consult the Samsung Mobile Security Site and Samsung Mobile Security Updates page. This vulnerability is also tracked in the CISA Known Exploited Vulnerabilities Catalog.

Workarounds

• Limit application installation permissions on corporate-managed devices to prevent installation of untrusted applications
• Implement network-level controls to prevent communication with known malicious command and control servers
• Use Samsung Knox containerization to isolate sensitive data from potentially compromised application environments
• Conduct regular security audits of installed applications on managed device fleets

# Check Android security patch level on Samsung device
# Navigate to: Settings > About Phone > Software Information
# Verify "Android Security Patch Level" is March 2021 or later

# For enterprise MDM, enforce minimum patch level policy:
# Samsung Knox policy example - require SMR-Mar-2021 or newer