CVE-2021-25337

What it actually does

This is an improper access control flaw in the Samsung clipboard service on affected Android-based Samsung mobile devices prior to Samsung Mobile Security Release (SMR) Mar-2021 Release 1. A local untrusted application can abuse the clipboard service to read or write certain local files without having the permissions that should normally be required. The impact is local to the device but can result in high confidentiality and integrity compromise because the attacker-controlled app may access sensitive file content or modify files used by other applications or device components.

Why it matters to the business

Organizations with unpatched Samsung Android devices may face mobile data exposure, unauthorized modification of local files, loss of trust in mobile-managed workflows, and potential compliance issues if business data is stored or processed on affected devices. The vulnerability is listed in CISA KEV and has been observed as actively exploited in the wild, so it should be treated as higher priority than its relatively low EPSS score alone suggests. CISA required remediation by 2022-11-29 for covered organizations, and any remaining exposed devices represent long-lived, known-risk endpoints.

How an attack unfolds

An attacker first gets a malicious or repackaged application onto a vulnerable Samsung device, typically through sideloading, a third-party app store, phishing, or social engineering that convinces the user to install or interact with the app. Because the flaw requires local execution and user interaction but no prior privileges, the malicious app does not need elevated Android permissions to begin exploitation. The app then invokes or interacts with the vulnerable clipboard service in a way that bypasses intended access controls, allowing it to read from or write to certain local files. Read access can be used to collect sensitive device or application data for exfiltration, while write access can be used to tamper with local files, alter application behavior, or stage follow-on activity. Exploitation is device-side and may leave limited centralized evidence unless mobile EDR, EMM/MDM telemetry, application inventory, device logs, or network monitoring are available.

How to fix it

Update affected Samsung mobile devices to SMR Mar-2021 Release 1 or later through the device OEM/carrier firmware update channel. Where possible, require a current Android/Samsung security patch level through EMM/MDM compliance policy and block access to corporate resources from devices below the fixed patch level. If devices cannot be updated, retire or isolate them from sensitive applications and data. Remove untrusted or unnecessary applications, disable or restrict sideloading, enforce managed app stores, and use mobile threat defense controls to detect malicious applications. For suspected exploitation, preserve device state where feasible, collect mobile EDR/MDM telemetry, review installed applications, and consider factory reset or device replacement after evidence collection.

How to confirm the fix worked

Confirm that Samsung devices report a security patch level at or after the vendor fix corresponding to SMR Mar-2021 Release 1. Validate through device settings, EMM/MDM inventory, Samsung firmware build reporting, or mobile threat defense posture checks rather than relying only on user attestation. Confirm that devices running older firmware are quarantined, blocked from corporate access, or removed from service. For application-control validation, verify that sideloading is disabled or restricted, only approved app sources are allowed, and unknown or unmanaged applications are flagged. If performing security testing, use a controlled test device and verify that an untrusted application can no longer use the clipboard service to read or write protected local files outside its intended access scope.

Typical attack path

1. Identify users or devices likely to be running Samsung firmware older than SMR Mar-2021 Release 1.
2. Deliver a malicious or repackaged Android application through sideloading, phishing, an unofficial app store, or another social-engineering path.
3. Convince the user to install or open the application, satisfying the local execution and user-interaction requirements.
4. From the untrusted app, interact with the vulnerable Samsung clipboard service to bypass intended file access restrictions.
5. Read sensitive local files or write attacker-controlled content to files that should not be accessible to the app.
6. Optionally exfiltrate collected data over the network or use modified files to support persistence, tampering, or additional device compromise.

How to detect it

Detection should focus on evidence that an untrusted local Android application was installed and then accessed sensitive local files or generated suspicious outbound traffic. Useful sources include EMM/MDM device inventory and compliance records, mobile threat defense alerts, Android application install/uninstall history, Samsung device security patch reporting, Play Protect or managed app-store telemetry, logcat captures where available, endpoint/network telemetry from managed mobile VPNs, DNS/proxy logs, and CASB or identity logs showing unusual access immediately after mobile app installation. Look for devices below SMR Mar-2021 Release 1 that have recently installed unknown APKs, apps from non-managed sources, or apps with suspicious behavior such as reading local content and contacting unfamiliar domains. On devices available for forensic review, examine installed package lists, APK acquisition sources, app data directories, recent file modification times, clipboard-service-related logs if retained, and network activity from non-corporate applications. Because no public, unique exploit string is inherent to this vulnerability, absence of a specific IOC match should not be considered evidence of non-exploitation.

What your security team should do

• Treat this as a priority mobile endpoint issue because it is in CISA KEV and has active in-the-wild exploitation, despite a low and flat EPSS trend of 0.0283 over 30 days.
• Inventory Samsung Android devices and identify any running firmware older than SMR Mar-2021 Release 1.
• Enforce minimum patch-level compliance through EMM/MDM and block non-compliant devices from corporate email, VPN, SSO, and managed applications.
• Restrict sideloading and third-party app-store installation, especially on devices that access business data.
• Review installed application inventories for unknown, recently installed, unmanaged, or suspiciously permission-light apps that appeared before or around suspicious activity.
• Enable or tune mobile threat defense, EDR, and network monitoring to detect suspicious local file access followed by outbound data transfer from mobile applications.
• For devices suspected of compromise, preserve available telemetry, remove suspicious apps, rotate credentials used on the device, and reimage, factory reset, or replace the device after triage.
• Communicate to users that unexpected app-install prompts, APK files, and unofficial mobile apps are high-risk on unpatched devices.