CVE-2021-25337

What is the Samsung Clipboard Service?

Samsung Galaxy devices include a clipboard service that manages copy-and-paste operations across applications. This service maintains clipboard data and provides system-level access to clipboard contents for applications with appropriate permissions. In some Samsung implementations, the clipboard service is accessible to applications without requiring the same privilege level as other system services — creating an improper access control condition (CWE-269: Improper Privilege Management) where applications with lower-than-expected privilege can interact with the clipboard service in ways that extend beyond normal clipboard functionality, including reading from and writing to arbitrary files on the device filesystem.

Overview

CVE-2021-25337 is an improper access control vulnerability (CWE-269) in Samsung Galaxy's clipboard service that allows an untrusted application (requiring user interaction but no special privileges) to read or write arbitrary files on the device filesystem. In isolation, the file read/write capability is a significant privilege escalation for an app that should only access its own sandbox. As the first stage of a three-CVE Samsung exploit chain alongside CVE-2021-25369 (Mali GPU sec_log kernel info leak) and CVE-2021-25370 (DPU driver memory corruption), CVE-2021-25337 provides the file access capability needed to support kernel exploitation. All three CVEs were patched in Samsung's March 2021 Security Bulletin. CISA added them to KEV in November 2022.

Affected Versions

Technical Details

• Root cause: Improper privilege management (CWE-269) in Samsung's clipboard service — the service exposes file system access operations to calling processes without adequate privilege verification; an application that should only have access to its own sandboxed storage can interact with the clipboard service in a way that reads or writes files outside its sandbox
• UI:R (user interaction): Exploitation requires the victim to perform some action that triggers the vulnerability path — possibly opening a malicious app or interacting with content that invokes the clipboard service in the vulnerable way; this is a common requirement for Android privilege escalation chains where the initial step requires user interaction to install or run an app
• Chain role — file access primitive: In the three-CVE chain (CVE-2021-25337 + CVE-2021-25369 + CVE-2021-25370), CVE-2021-25337 provides the ability to read and write device files, enabling: (1) reading kernel info from files accessible to the clipboard service (supporting KASLR defeat alongside CVE-2021-25369's Mali GPU sec_log info leak), (2) writing exploit payloads to locations accessible to kernel drivers for use with CVE-2021-25370's DPU driver memory corruption
• Targeted surveillance context: The combination of Samsung-specific clipboard service access, GPU info leak, and kernel memory corruption suggests an exploit chain designed for targeted surveillance against Samsung Galaxy users — consistent with commercial mobile surveillance vendor tooling targeting common enterprise and government Android devices
• November 2022 KEV addition: CISA's addition nearly 20 months after the patch reflects confirmed in-the-wild exploitation for surveillance purposes — consistent with commercial spyware vendors whose products may still target unpatched Samsung devices

Discovery

Patched in Samsung's March 2021 Security Bulletin alongside CVE-2021-25369 and CVE-2021-25370. CISA's November 2022 KEV addition (simultaneous with CVE-2021-25369 and CVE-2021-25370) indicates the three-CVE chain was discovered as a complete, deployed exploitation framework targeting Samsung Galaxy devices — likely documented during forensic investigation of surveillance attack against high-value targets.

Exploitation Context

Samsung Galaxy devices are the dominant Android platform in enterprise and government environments globally. Exploit chains targeting Samsung-specific kernel drivers and system services are primarily used in targeted mobile surveillance operations (espionage campaigns against government officials, journalists, or dissidents). CVE-2021-25337's role as the file access entry point makes it the prerequisite for the more severe memory corruption in CVE-2021-25370 — without the file write capability, the kernel exploitation step would require a different access mechanism. The coordinated CISA KEV listing of all three CVEs confirms they were observed and used as a complete chain.

Remediation

1. Apply Samsung March 2021 Security Bulletin updates — patches CVE-2021-25337, CVE-2021-25369, and CVE-2021-25370 together, breaking the exploitation chain
2. Verify security patch level is 2021-03-01 or later: Settings → About Phone → Android Security Update
3. Enable automatic Samsung security updates to ensure timely patch application
4. For enterprise MDM: enforce minimum security patch level via Samsung Knox MDM policies
5. For high-risk individuals: verify Samsung security patch level immediately and update if below March 2021; consider using Samsung devices with current security patch levels
6. Samsung Galaxy devices that no longer receive security updates remain permanently vulnerable to this chain — replace end-of-life devices