CVE-2026-21071: MPEG4 Codec Buffer Overflow Vulnerability

CVE-2026-21071 Overview

CVE-2026-21071 is an improper input validation vulnerability in the MPEG4 codec implementation within libsavsvc.so on Samsung mobile devices. The flaw allows local attackers to write out-of-bounds memory when processing crafted MPEG4 media data. Samsung addressed the issue in the SMR Aug-2026 Release 1 security maintenance update. The vulnerability is categorized under [CWE-20] Improper Input Validation and requires local access with no user interaction to exploit.

Critical Impact
Local attackers can trigger out-of-bounds memory writes in the MPEG4 codec, potentially corrupting adjacent memory regions and compromising the integrity of the media service process.

Affected Products

Samsung mobile devices running firmware prior to SMR Aug-2026 Release 1
libsavsvc.so MPEG4 codec component
Samsung Android media framework services

Discovery Timeline

2026-08-10 - CVE-2026-21071 published to NVD
2026-08-10 - Last updated in NVD database

Technical Details for CVE-2026-21071

Vulnerability Analysis

The vulnerability resides in the MPEG4 codec parsing logic implemented in libsavsvc.so, a Samsung media service library. When the codec processes MPEG4 container structures, it fails to properly validate size or offset fields supplied through the input stream. This missing validation permits write operations to reference memory locations outside the intended buffer boundary.

An attacker with local access to the device can supply a malformed MPEG4 stream to the media service. Because the codec runs within a privileged media process, out-of-bounds writes may corrupt heap metadata, function pointers, or adjacent objects. The impact spans confidentiality, integrity, and availability at limited scope, consistent with a local escalation primitive rather than a remote code execution flaw.

Root Cause

The root cause is missing or insufficient bounds checking on attacker-controlled length or offset fields during MPEG4 atom parsing. The codec trusts values in the media container without validating them against the actual allocated buffer size before performing write operations.

Attack Vector

Exploitation requires local access. The attack vector is limited to a malicious application installed on the device or a local process that can deliver a crafted MPEG4 file to the vulnerable codec. No user interaction and no elevated privileges are required to trigger the parsing path. Samsung has not published exploitation details, and no public proof-of-concept is available at this time. Refer to the Samsung Mobile Security Update for vendor-supplied technical context.

Detection Methods for CVE-2026-21071

Indicators of Compromise

Unexpected crashes or restarts of Samsung media service processes referencing libsavsvc.so in tombstone logs
Malformed MPEG4 files staged in application-accessible storage locations shortly before media service instability
Installation of untrusted third-party applications that programmatically invoke the media codec with attacker-supplied files

Detection Strategies

Monitor Android system logs and native crash dumps for SIGSEGV or SIGABRT signals originating in the MPEG4 codec path within libsavsvc.so
Track deployment status of the SMR Aug-2026 Release 1 firmware across the mobile fleet using MDM inventory data
Correlate media service process anomalies with recent application installs or side-loaded APKs

Monitoring Recommendations

Enable enterprise mobile threat defense telemetry to flag apps that invoke media codecs on malformed files
Ingest Samsung Knox or MDM audit logs into a central analytics platform to identify devices missing the August 2026 patch
Alert on repeated media service crashes on the same device, which may indicate exploitation attempts against the codec

How to Mitigate CVE-2026-21071

Immediate Actions Required

Apply the Samsung SMR Aug-2026 Release 1 security maintenance update to all affected devices
Inventory managed Samsung mobile devices and prioritize patch deployment for models still receiving Samsung security maintenance releases
Restrict installation of untrusted applications through MDM policies until patching is complete

Patch Information

Samsung addressed CVE-2026-21071 in the SMR Aug-2026 Release 1 firmware update. Details and the list of affected models are published in the Samsung Mobile Security Update bulletin for August 2026. Administrators should push the update through Samsung Knox, carrier OTA channels, or their enterprise MDM.

Workarounds

Block installation of applications from unknown sources through MDM configuration profiles
Avoid opening MPEG4 media files received from untrusted senders or downloaded from untrusted websites
Enforce Samsung Knox application allow-listing to prevent execution of untrusted code that could invoke the vulnerable codec

bash

# Verify current Samsung security patch level on a managed device
adb shell getprop ro.build.version.security_patch
adb shell getprop ro.build.PDA

# Expected result: security patch level dated 2026-08-01 or later