CVE-2026-20464: HEVC Decoder Privilege Escalation Flaw

CVE-2026-20464 Overview

CVE-2026-20464 is an out-of-bounds write vulnerability in the High Efficiency Video Coding (HEVC) decoder. The flaw stems from an integer overflow during video frame processing. An attacker with existing System privileges can trigger the overflow to escalate privileges further on the affected device. User interaction is not required for exploitation.

MediaTek disclosed the issue in its August 2026 Product Security Bulletin under Patch ID ALPS11104718 and Issue ID MSV-8297. The weakness is classified as [CWE-787] Out-of-Bounds Write.

Critical Impact
An attacker holding System privileges can escalate to a higher trust boundary through crafted HEVC media, without any user interaction on the target device.

Affected Products

MediaTek chipsets exposing the HEVC decoder component referenced in the August 2026 Product Security Bulletin
Android devices integrating the vulnerable MediaTek HEVC decoder firmware
Downstream OEM builds that have not applied Patch ID ALPS11104718

Discovery Timeline

2026-08-03 - CVE-2026-20464 published to the National Vulnerability Database (NVD)
2026-08-05 - Last updated in NVD database

Technical Details for CVE-2026-20464

Vulnerability Analysis

The defect is an integer overflow inside the HEVC decoder that leads to an out-of-bounds write [CWE-787]. When the decoder computes a buffer size or index using attacker-influenced values from an HEVC bitstream, an arithmetic wrap causes the resulting allocation or offset to be smaller than the data eventually written.

The decoder then writes past the intended buffer boundary. The corrupted memory sits within a privileged process on the device, which allows the attacker to influence execution flow or overwrite security-relevant structures. Exploitation requires the attacker to already hold System privilege, which is why the impact is scoped to escalation rather than initial compromise.

The EPSS score is 0.353% with a percentile of 27.9, reflecting limited public exploit activity at disclosure.

Root Cause

The root cause is unchecked arithmetic on values parsed from an HEVC stream. Size or offset computations wrap around the native integer width. The decoder trusts the wrapped value and continues writing decoded pixel or metadata content beyond the allocated region.

Attack Vector

An attacker running with System privilege supplies a crafted HEVC media stream to the vulnerable decoder path. Because user interaction is not required, the crafted stream can be delivered by any System-context component that can invoke the decoder. Successful exploitation corrupts memory in the decoder's process and enables privilege escalation beyond the System boundary.

No verified public proof-of-concept code is available. Refer to the MediaTek Security Bulletin August 2026 for vendor technical details.

Detection Methods for CVE-2026-20464

Indicators of Compromise

Unexpected crashes or SIGSEGV signals in the HEVC decoder process during media parsing
Presence of unpatched builds missing MediaTek Patch ID ALPS11104718
Anomalous System-privileged processes invoking media codec interfaces outside normal playback flows

Detection Strategies

Monitor Android media server and codec processes for repeated abnormal terminations correlated with HEVC content
Compare device firmware and security patch level against the MediaTek August 2026 bulletin baseline
Inspect logs for malformed HEVC NAL units or decoder errors preceding process restarts

Monitoring Recommendations

Centralize device telemetry, including kernel and codec logs, into a SIEM for correlation across the fleet
Alert on System-context processes loading or invoking the HEVC decoder outside expected media playback contexts
Track patch adoption rates per OEM build to identify devices still exposed to MSV-8297

How to Mitigate CVE-2026-20464

Immediate Actions Required

Apply the MediaTek security patch identified by Patch ID ALPS11104718 through the relevant OEM update channel
Confirm the device security patch level reflects the August 2026 MediaTek bulletin
Restrict the ability of non-essential System-context components to reach the HEVC decoder

Patch Information

MediaTek addresses the issue in Patch ID ALPS11104718, tracked internally as Issue ID MSV-8297. Consult the MediaTek Security Bulletin August 2026 for the fixed chipsets and integration guidance for OEM partners.

Workarounds

Avoid processing untrusted HEVC content on unpatched devices where possible
Enforce least-privilege controls to limit which components run with System privilege on affected devices
Prioritize deployment of vendor firmware updates for high-value or shared devices first

bash

# Verify Android security patch level on an affected device
adb shell getprop ro.build.version.security_patch

# Confirm MediaTek vendor patch metadata where available
adb shell getprop ro.vendor.build.security_patch