CVE-2026-56942: VP9 Decoder Privilege Escalation Vulnerability

CVE-2026-56942 Overview

CVE-2026-56942 is an out-of-bounds write vulnerability in the ReadTileInfo function of vp9hwd_headers.cc, a component of the Android VP9 hardware video decoder. The flaw stems from a missing bounds check during tile information parsing. An attacker can trigger the condition remotely without user interaction, leading to escalation of privilege on affected devices. The issue is tracked in the Android Security Bulletin for September 2026.

Critical Impact
Remote attackers can achieve privilege escalation on Android devices by delivering a crafted VP9 media stream, with no user interaction required and no additional execution privileges needed.

Affected Products

Android platform components including the VP9 hardware decoder (vp9hwd_headers.cc)
Google Pixel devices as referenced in the September 2026 Pixel Security Bulletin
OEM Android builds that ship the affected VP9 hardware decode library

Discovery Timeline

2026-09-15 - CVE-2026-56942 published to NVD
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-56942

Vulnerability Analysis

The vulnerability resides in ReadTileInfo, a function in vp9hwd_headers.cc responsible for parsing tile configuration data from VP9 bitstreams. The function processes tile row and column information used by the hardware decoder to partition frames for parallel decoding. Because a required bounds check is missing, malformed tile metadata causes the function to write past the end of an allocated buffer. This condition is classified under [CWE-787] Out-of-Bounds Write.

Exploitation results in remote escalation of privilege. The attacker gains elevated execution context within the media processing pipeline without needing user interaction or additional execution privileges beyond what a media rendering path already provides.

Root Cause

The root cause is the absence of a bounds validation step before writing tile information into a fixed-size structure. VP9 bitstreams encode tile_rows and tile_cols values that must be constrained before being used as indices or write offsets. When these values are not validated against buffer capacity, controlled data from the input stream can overwrite adjacent memory.

Attack Vector

Delivery vectors include any pathway that feeds VP9-encoded media into the hardware decoder. These include streamed video, messaging application attachments, browser-loaded content, and locally rendered media previews. Because user interaction is not required, background media processing or automatic preview generation is sufficient to reach the vulnerable parser.

No verified public proof-of-concept code is available at the time of publication. See the Android Security Bulletin September 2026 for technical references.

Detection Methods for CVE-2026-56942

Indicators of Compromise

Unexpected crashes or SIGSEGV signals originating from the media codec service (mediacodec, media.swcodec) when processing VP9 content
Tombstone files in /data/tombstones/ referencing vp9hwd_headers.cc or the ReadTileInfo symbol
Anomalous child processes or privilege transitions spawned from media server components after VP9 playback

Detection Strategies

Inspect VP9 bitstream headers at network or application boundaries for tile row and column counts that exceed VP9 specification limits
Correlate media codec crashes with subsequent process behavior changes to identify successful exploitation attempts
Monitor Android device logs for repeated codec restarts triggered by malformed video payloads

Monitoring Recommendations

Aggregate mobile device crash telemetry centrally and alert on clustered failures within VP9 decode paths
Track outbound connections initiated by processes downstream of the media pipeline for signs of post-exploitation activity
Baseline normal media codec memory usage and flag deviations that indicate memory corruption

How to Mitigate CVE-2026-56942

Immediate Actions Required

Apply the September 2026 Android security patch level or later on all managed Android devices
Prioritize patching of devices that render untrusted video content such as messaging clients, browsers, and social media applications
Enforce mobile device management policies that block enrollment or access for devices below the required patch level

Patch Information

Google addressed the vulnerability in the September 2026 Android Security Bulletin. Refer to the Android Security Bulletin September 2026 for the specific patch level and source code references. Device OEMs incorporate the fix into their monthly security updates on staggered schedules.

Workarounds

Disable automatic media preview and autoplay features in messaging and email applications until patches are applied
Restrict installation of applications that process untrusted VP9 video from unverified sources
Use MDM policies to enforce Play Protect and restrict sideloading on corporate devices

bash

# Verify current Android security patch level on a managed device
adb shell getprop ro.build.version.security_patch
# Expected output for remediated devices: 2026-09-01 or later