CVE-2026-21091: libcodec2secevrcdec Buffer Overflow Flaw

CVE-2026-21091 Overview

CVE-2026-21091 is an out-of-bounds write vulnerability in the libcodec2secevrcdec.so shared library on Samsung mobile devices. The flaw exists in versions prior to the Samsung Mobile Release (SMR) September 2026 Release 1. A local attacker with low privileges can trigger the vulnerability to write data outside the bounds of an allocated memory buffer. The issue is tracked under CWE-787: Out-of-bounds Write and affects the Secure Enhanced Variable Rate Codec (SEVRC) decoder component used for audio processing.

Critical Impact
Local attackers can corrupt adjacent memory in the codec library, potentially leading to application instability, denial of service, or exploitation for arbitrary code execution within the affected process context.

Affected Products

Samsung mobile devices running firmware prior to SMR Sep-2026 Release 1
The libcodec2secevrcdec.so shared library (SEVRC audio decoder)
Android-based Samsung Galaxy devices dependent on the vulnerable codec component

Discovery Timeline

2026-09-09 - CVE-2026-21091 published to NVD
2026-09-10 - Last updated in NVD database

Technical Details for CVE-2026-21091

Vulnerability Analysis

The vulnerability resides in libcodec2secevrcdec.so, a native shared library that handles Secure Enhanced Variable Rate Codec (SEVRC) audio decoding on Samsung devices. An out-of-bounds write occurs when the decoder processes crafted input and writes data beyond the boundary of an allocated buffer.

An attacker requires local access and low privileges to reach the vulnerable code path. No user interaction is needed. Successful triggering corrupts adjacent memory regions within the process address space. The scope of impact is confined to the process loading the vulnerable library.

Root Cause

The root cause is missing or insufficient bounds validation during codec buffer operations, categorized under CWE-787: Out-of-bounds Write. The decoder writes attacker-influenced data past the end of a fixed-size buffer, corrupting neighboring heap or stack structures. Samsung has not published the specific function or offset where the boundary check is absent.

Attack Vector

Exploitation requires local code execution on the target device, typically through an installed application with low privileges. The malicious application supplies crafted input to the SEVRC decoder to trigger the boundary violation. Because the codec is invoked through media processing APIs, an attacker can reach the vulnerable code without holding elevated permissions. See the Samsung Security Update September 2026 for vendor-specific details.

Detection Methods for CVE-2026-21091

Indicators of Compromise

Repeated crashes or SIGSEGV faults in processes that load libcodec2secevrcdec.so
Tombstone files in /data/tombstones/ referencing the SEVRC codec library
Installed applications that request media processing permissions and invoke SEVRC decoding without a clear functional need

Detection Strategies

Monitor Android system logs (logcat) and crash reports for native aborts tied to the codec library
Inspect application packages for calls into media codec APIs that decode SEVRC content from untrusted sources
Correlate device firmware build numbers against the SMR Sep-2026 Release 1 baseline to identify unpatched endpoints in mobile device management (MDM) inventories

Monitoring Recommendations

Enroll Samsung devices in an MDM platform that reports the Android security patch level and enforces minimum firmware versions
Alert on applications that repeatedly crash media services, as this can indicate exploitation attempts against native codec libraries
Review mobile threat defense telemetry for anomalous native-library crashes correlated with newly installed applications

How to Mitigate CVE-2026-21091

Immediate Actions Required

Apply the Samsung Mobile Release SMR Sep-2026 Release 1 update to all affected devices as soon as it is available for the specific model
Restrict installation of untrusted applications by enforcing Google Play Protect and disabling sideloading through MDM policy
Audit installed applications for unnecessary media codec access and remove any that are not required for business operations

Patch Information

Samsung addressed the vulnerability in SMR Sep-2026 Release 1. Consult the Samsung Security Update September 2026 bulletin to confirm which device models have received the fix in your region. Users should install pending firmware updates through Settings > Software update > Download and install.

Workarounds

No vendor-supplied workaround has been published; apply the firmware update as the primary remediation
Limit exposure by avoiding untrusted audio content and applications that process arbitrary SEVRC streams
Enforce application allow-listing on managed devices to prevent installation of applications that could reach the vulnerable codec

bash

# Check the Android security patch level on a Samsung device via ADB
adb shell getprop ro.build.version.security_patch
adb shell getprop ro.build.PDA

# Verify the vulnerable library is present and inspect its properties
adb shell ls -la /system/lib64/libcodec2secevrcdec.so