CVE-2021-25487: Samsung Android RCE Vulnerability

CVE-2021-25487 Overview

CVE-2021-25487 is an out-of-bounds read vulnerability in the Samsung Android modem interface driver that enables arbitrary code execution through the dereferencing of an invalid function pointer. The flaw exists in the set_skb_priv() function, which fails to perform adequate boundary checking on buffer operations. This vulnerability has been confirmed as actively exploited in the wild and is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, making it a priority for immediate remediation.

Critical Impact

Successful exploitation allows local attackers with low privileges to achieve arbitrary code execution by triggering an out-of-bounds read that results in the dereferencing of an invalid function pointer, potentially leading to full device compromise.

Affected Products

• Samsung Android 8.1
• Samsung Android 9.0 (SMR releases prior to October 2021)
• Samsung Android 10.0 (SMR releases prior to October 2021)
• Samsung Android 11.0 (SMR releases prior to October 2021)

Discovery Timeline

• October 6, 2021 - CVE CVE-2021-25487 published to NVD
• October 30, 2025 - Last updated in NVD database

Technical Details for CVE-2021-25487

Vulnerability Analysis

This vulnerability stems from insufficient boundary validation within the modem interface driver, a critical kernel-level component responsible for managing communication between the Android operating system and the device's cellular modem. The set_skb_priv() function processes socket buffer (SKB) private data structures without properly validating buffer boundaries, creating conditions for an out-of-bounds memory read.

When the out-of-bounds read occurs, the attacker can manipulate memory to cause the dereferencing of an invalid function pointer. Because function pointers are used to direct program execution flow, controlling this value allows attackers to redirect execution to arbitrary code of their choosing. Given that this vulnerability exists at the kernel driver level, successful exploitation can lead to privilege escalation and complete device compromise.

The local attack vector means an attacker requires some level of access to the device, such as through a malicious application or by chaining with another vulnerability that provides initial access. This vulnerability has been confirmed as actively exploited in the wild, as documented by CISA's inclusion in the Known Exploited Vulnerabilities catalog.

Root Cause

The root cause is a classic boundary checking failure (CWE-125: Out-of-bounds Read) in the set_skb_priv() function within Samsung's modem interface driver. The function processes buffer data without validating that read operations stay within allocated memory bounds, allowing reads beyond the intended buffer limits. This improper input validation enables memory corruption scenarios that can be leveraged for arbitrary code execution.

Attack Vector

The attack requires local access to the device and low privileges. An attacker can trigger the vulnerability by sending specially crafted data through the modem interface that causes the set_skb_priv() function to read beyond buffer boundaries. The out-of-bounds read corrupts a function pointer, and when this invalid pointer is subsequently dereferenced, execution is redirected to attacker-controlled code. This can be achieved through a malicious application installed on the device or by chaining with another vulnerability that provides initial code execution.

Detection Methods for CVE-2021-25487

Indicators of Compromise

• Unexpected crashes or reboots of the modem interface or related system services
• Anomalous system log entries referencing the modem driver or kernel memory errors
• Detection of unauthorized applications attempting to interact with modem interfaces
• Signs of privilege escalation or unauthorized root access on Samsung devices
• Unusual network activity originating from the modem interface

Detection Strategies

• Monitor for kernel panic events or crash dumps related to modem driver operations
• Deploy mobile device management (MDM) solutions capable of detecting kernel-level anomalies
• Implement endpoint detection and response (EDR) solutions with Android kernel monitoring capabilities
• Use Samsung Knox security features to detect tampering or exploitation attempts

Monitoring Recommendations

• Enable enhanced logging for kernel-level operations on managed Samsung devices
• Monitor for applications requesting unusual permissions related to modem or telephony interfaces
• Implement security policies that restrict installation of applications from untrusted sources
• Regularly review device security posture through MDM dashboards

How to Mitigate CVE-2021-25487

Immediate Actions Required

• Update all affected Samsung Android devices to SMR October 2021 Release 1 or later immediately
• Prioritize patching given this vulnerability is listed in the CISA KEV catalog
• Restrict device access and limit installation of third-party applications until patched
• Review devices for signs of compromise before and after applying patches
• Ensure enterprise MDM policies enforce automatic security updates

Patch Information

Samsung has addressed this vulnerability in the SMR (Samsung Mobile Release) October 2021 Release 1 security update. Organizations and individuals should update affected devices to the October 2021 security patch level or later. The official security advisory is available through the Samsung Security Update October 2021 page. Given the confirmed exploitation in the wild and CISA KEV listing, this patch should be treated as an emergency priority.

Workarounds

• Limit device access to trusted users and applications until patching is complete
• Disable or restrict installation of applications from unknown sources
• Implement network-level controls to monitor and restrict suspicious modem-related traffic
• Consider temporary isolation of unpatched devices from sensitive networks
• Use Samsung Knox containerization to isolate sensitive data from potential exploitation

# Check Samsung device security patch level
# Navigate to: Settings > About phone > Software information
# Verify "Android security patch level" shows October 2021 or later

# For enterprise MDM administrators (example policy enforcement)
# Ensure compliance policy requires minimum patch level: 2021-10-01