CVE-2026-21093: PROCA Trustlet Buffer Overflow Vulnerability

CVE-2026-21093 Overview

CVE-2026-21093 is a stack-based buffer overflow [CWE-121] in the PROCA trustlet on Samsung mobile devices prior to Security Maintenance Release (SMR) Sep-2026 Release 1. The flaw allows a local, privileged attacker to write out-of-bounds memory within the trusted execution environment (TEE). Samsung addressed the issue in its September 2026 security maintenance release.

PROCA (Process Authenticator) is a Samsung TrustZone trustlet responsible for validating process integrity on Android. Exploitation requires local access with elevated privileges and high attack complexity, limiting practical exploitation but still exposing sensitive trustlet memory to corruption.

Critical Impact
Successful exploitation can corrupt memory inside a TrustZone trustlet, potentially undermining process authentication integrity on affected Samsung devices.

Affected Products

Samsung Mobile devices running the PROCA trustlet prior to SMR Sep-2026 Release 1
Samsung Android builds released before the September 2026 security maintenance release
Devices that have not applied the Samsung Mobile Security September 2026 update

Discovery Timeline

2026-09-09 - CVE-2026-21093 published to the National Vulnerability Database (NVD)
2026-09-10 - Last updated in NVD database

Technical Details for CVE-2026-21093

Vulnerability Analysis

The vulnerability is a stack-based buffer overflow inside the PROCA trustlet, a component running in the ARM TrustZone secure world on Samsung mobile devices. When PROCA processes attacker-controlled input on a fixed-size stack buffer, it writes past the buffer's bounds. This corrupts adjacent stack memory, including saved return addresses and local variables within the trustlet's execution context.

Because PROCA executes in the secure world, out-of-bounds writes inside the trustlet can influence data used to authenticate Android processes. The classification under [CWE-121] identifies the root failure as insufficient bounds checking on stack-allocated buffers during trustlet request handling.

Exploitation requires local access and elevated privileges on the Android side. The attacker must already control a privileged process capable of invoking the trustlet through the appropriate Secure Monitor Call (SMC) interface.

Root Cause

The root cause is missing or incorrect length validation on data copied into a stack buffer within the PROCA trustlet. The trustlet trusts a length or size field originating from the non-secure world without enforcing an upper bound against the destination buffer size.

Attack Vector

An attacker with local privileged access on the device crafts a request to the PROCA trustlet containing an oversized payload. The trustlet copies the payload into a stack buffer, overwriting return addresses or control data. High attack complexity applies because the attacker must satisfy trustlet-specific request formats and bypass secure-world mitigations such as stack canaries or address randomization. Samsung has not published exploitation details, and no public proof-of-concept is available.

Detection Methods for CVE-2026-21093

Indicators of Compromise

Unexpected trustlet crashes or resets logged by the TEE driver in dmesg or Android system logs
Abnormal SMC traffic volume from privileged Android processes targeting the PROCA trustlet
Devices reporting a pre-September 2026 SMR patch level in ro.build.version.security_patch

Detection Strategies

Inventory Samsung mobile devices in the fleet and compare reported patch levels against SMR Sep-2026 Release 1
Monitor mobile device management (MDM) compliance dashboards for devices lagging on Samsung security maintenance releases
Correlate crash telemetry from TrustZone components with privileged process activity to identify anomalous trustlet interactions

Monitoring Recommendations

Enroll Samsung devices in an MDM or unified endpoint management platform that tracks security patch levels
Alert on any device that remains on a security patch level older than September 2026 beyond a defined grace period
Review privileged application installations and root-enabled devices, since exploitation requires elevated local privileges

How to Mitigate CVE-2026-21093

Immediate Actions Required

Apply Samsung Mobile Security Maintenance Release SMR Sep-2026 Release 1 or later to all affected devices
Restrict installation of untrusted or side-loaded applications that could obtain privileged access
Enforce MDM policies that block rooted devices from accessing corporate resources

Patch Information

Samsung released the fix in the September 2026 Security Maintenance Release. Details are available in the Samsung Security Update September 2026 advisory. Deploy the update through carrier over-the-air (OTA) channels or enterprise MDM policies.

Workarounds

No vendor-supplied workaround exists; patching is the only supported remediation
Reduce exposure by limiting privileged app installations and disabling developer options on managed devices
Enforce conditional access that requires an up-to-date Android security patch level before granting access to sensitive resources

bash

# Verify the Android security patch level on a connected Samsung device
adb shell getprop ro.build.version.security_patch
# Expected value after remediation: 2026-09-01 or later