CVE-2026-56920 Overview
CVE-2026-56920 is an out-of-bounds write vulnerability in the s_decode_vui_param function within fw_hevc_dec_header.c. The flaw results from a logic error in the High Efficiency Video Coding (HEVC) decoder's Video Usability Information (VUI) parameter parsing routine. Successful exploitation allows remote code execution without additional execution privileges. The vulnerability requires no user interaction, meaning a crafted HEVC media stream can trigger the flaw when processed by the decoder. The issue is addressed in the Android Security Bulletin September 2026.
Critical Impact
A remote attacker can achieve code execution on affected devices by delivering a malicious HEVC video stream, with no user interaction required.
Affected Products
- Android platform components processing HEVC video (Pixel devices per September 2026 bulletin)
- Firmware fw_hevc_dec_header decoder module
- Devices consuming media through the affected HEVC decoder library
Discovery Timeline
- 2026-09-15 - CVE-2026-56920 published to the National Vulnerability Database
- 2026-09-16 - Last updated in NVD database
Technical Details for CVE-2026-56920
Vulnerability Analysis
The vulnerability resides in s_decode_vui_param, a routine responsible for decoding VUI parameters within the HEVC bitstream header. VUI parameters carry auxiliary information such as aspect ratio, timing, and color descriptors that a decoder uses to render video correctly. A logic error in the parsing path allows a write to occur outside the intended buffer boundaries.
The weakness is classified under [CWE-787] Out-of-bounds Write. Memory corruption in a media parser reachable from network-delivered content is a high-value target for attackers because media pipelines are frequently invoked automatically by messaging, browser, and streaming applications.
Root Cause
The root cause is a logic error in the VUI parameter decoding function. The routine fails to correctly validate size or index values derived from attacker-controlled bitstream fields before writing to a destination buffer. When crafted values are supplied, the decoder writes past the allocated memory region, corrupting adjacent structures. Attackers can shape this corruption to hijack control flow and execute arbitrary code within the media process context.
Attack Vector
The attack vector is network-based. An attacker delivers a specially crafted HEVC video stream through any channel that triggers automatic media parsing, such as multimedia messaging, web content, or streaming applications. Because exploitation requires no user interaction, the corruption occurs during automated header parsing before playback begins. The attacker needs low privileges on the target, consistent with sending content that a media component subsequently processes.
No public proof-of-concept exploit is available at the time of publication, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. Refer to the Android Security Bulletin September 2026 for technical fix details.
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Stop Exploit AttemptsDetection Methods for CVE-2026-56920
Indicators of Compromise
- Unexpected crashes or restarts of media parsing services and decoder processes handling HEVC content
- Anomalous child processes spawned by media server components following HEVC playback
- Native crash logs referencing s_decode_vui_param or fw_hevc_dec_header
- Inbound HEVC streams from untrusted origins delivered through messaging or web content
Detection Strategies
- Monitor endpoint telemetry for crashes in media decoder processes correlated with inbound HEVC content
- Inspect network traffic for HEVC bitstreams containing malformed VUI parameter fields
- Correlate media process anomalies with subsequent process creation or network activity indicative of post-exploitation
Monitoring Recommendations
- Enable behavioral monitoring on mobile management platforms to flag media component crashes and privilege changes
- Ingest device crash logs into a centralized data lake for cross-fleet correlation of decoder failures
- Track patch level compliance against the September 2026 Android security bulletin across managed devices
How to Mitigate CVE-2026-56920
Immediate Actions Required
- Apply the September 2026 Android security patch level to all affected devices as soon as it is available from the device vendor
- Inventory managed Android and Pixel devices and prioritize updates for high-risk users
- Restrict automatic media processing from untrusted sources where feasible through messaging application settings
Patch Information
The fix is included in the September 2026 Android security patch level. Consult the Android Security Bulletin September 2026 for the specific patch identifiers and affected component versions. Device manufacturers distribute the patch through their normal over-the-air update channels.
Workarounds
- Disable automatic download and preview of media attachments in messaging applications until patches are applied
- Avoid opening HEVC video content from untrusted senders or unknown websites
- Route mobile traffic through inspection proxies that can filter or block malformed HEVC streams
# Verify Android security patch level on a managed device
adb shell getprop ro.build.version.security_patch
# Expected output should be 2026-09-01 or later
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
