CVE-2021-25356
📋 TL;DR
CVE-2021-25356 is an improper caller check vulnerability in Samsung's Managed Provisioning service that allows unprivileged applications to install arbitrary apps, grant device admin permissions, and delete installed applications. This affects Samsung Android devices prior to the April 2021 security update. Attackers can gain elevated privileges and compromise device security.
💻 Affected Systems
- Samsung Android devices with Managed Provisioning
📦 What is this software?
Android by Google
Android by Google
Android by Google
Android by Google
⚠️ Risk & Real-World Impact
Worst Case
Complete device takeover: attacker installs malicious apps with device admin privileges, steals sensitive data, disables security controls, and bricks the device by deleting critical system apps.
Likely Case
Malicious app installation leading to data theft, surveillance, or ransomware deployment through elevated privileges.
If Mitigated
Limited impact if device is patched; unprivileged apps cannot exploit the vulnerability to gain admin rights.
🎯 Exploit Status
Exploitation requires installing a malicious app; detailed technical analysis is publicly available in the Oversecured blog posts.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: SMR APR-2021 Release 1 (April 2021 security patch) or later
Vendor Advisory: https://security.samsungmobile.com/securityUpdate.smsb
Restart Required: Yes
Instructions:
1. Check for system updates in device Settings > Software update. 2. Install the April 2021 security patch or later. 3. Restart the device after installation.
🔧 Temporary Workarounds
Disable unknown sources
androidPrevent installation of apps from unknown sources to reduce attack surface.
Settings > Security > Install unknown apps > Disable for all apps
Use Mobile Device Management (MDM)
allEnforce app whitelisting and block unauthorized app installations via MDM policies.
🧯 If You Can't Patch
- Restrict app installations to trusted sources only (e.g., official app stores).
- Monitor for suspicious app behavior and uninstall any unknown or unnecessary apps.
🔍 How to Verify
Check if Vulnerable:
Check Android security patch level: Settings > About phone > Software information > Android security patch level. If earlier than April 2021, device is likely vulnerable.Check Version:
adb shell getprop ro.build.version.security_patchVerify Fix Applied:
Confirm Android security patch level is April 2021 or later after applying update.📡 Detection & Monitoring
Log Indicators:
- Log entries showing unexpected app installations or device admin activations via Managed Provisioning.
- Package manager logs indicating privilege escalation attempts.
Network Indicators:
- Unusual network traffic from newly installed apps requesting elevated permissions.
SIEM Query:
source="android_logs" AND (event="app_install" OR event="admin_granted") AND app_name NOT IN (whitelist)🔗 References
- https://blog.oversecured.com/Two-weeks-of-securing-Samsung-devices-Part-1/
- https://security.samsungmobile.com/
- https://security.samsungmobile.com/securityUpdate.smsb
- https://blog.oversecured.com/Two-weeks-of-securing-Samsung-devices-Part-1/
- https://security.samsungmobile.com/
- https://security.samsungmobile.com/securityUpdate.smsb
