CVE-2026-56209: libaom AV1 Codec RCE Vulnerability

CVE-2026-56209 Overview

CVE-2026-56209 is an arbitrary address write vulnerability in libaom, the reference AV1 codec implementation maintained by the Alliance for Open Media. A missing bounds check in the Scalable Video Coding (SVC) layer ID control function allows an attacker to inject an arbitrary pointer into the cyclic_refresh map field through crafted image pixel values. The encoder then writes approximately 1,200 bytes at the attacker-controlled address. The flaw is fully deterministic and does not require a separate information leak to exploit.

Critical Impact
An attacker who can supply frames to a network-facing libaom encoder with SVC enabled can trigger denial of service or potential arbitrary code execution by writing ~1,200 bytes to a chosen memory address.

Affected Products

libaom — reference AV1 codec implementation (AOMedia)
Applications and services that link libaom with SVC encoding enabled
Downstream distributions tracked under Red Hat advisory for CVE-2026-56209

Discovery Timeline

2026-06-19 - CVE-2026-56209 published to NVD
2026-06-25 - Last updated in NVD database

Technical Details for CVE-2026-56209

Vulnerability Analysis

The vulnerability is classified as an out-of-bounds write [CWE-787] occurring inside the libaom AV1 encoder. The SVC layer ID control function accepts values derived from input image pixel data without validating them against expected bounds. When SVC is enabled, the encoder uses the layer ID to index or assign into the cyclic_refresh map field. An attacker who controls the pixel content of frames passed to the encoder can therefore steer a pointer used by the cyclic refresh subsystem.

Once the pointer is hijacked, the encoder writes roughly 1,200 bytes of cyclic refresh state to that location. Because the write is driven by encoder logic rather than a heap-corruption side effect, exploitation is deterministic across runs. This makes the bug suitable for both stable crashes and targeted memory corruption against function pointers, vtables, or adjacent heap metadata.

Root Cause

The root cause is a missing bounds check on the SVC layer ID before it is used to compute the destination of a structured write. The encoder trusts attacker-influenced input as a valid index or pointer feeder into cyclic_refresh, violating the principle of input validation at trust boundaries.

Attack Vector

The attack vector is network-reachable for any service that exposes a libaom-based AV1 encoder to externally supplied frames, such as media transcoding pipelines, WebRTC servers, or video conferencing backends. User interaction is required to initiate the encoding session. Successful exploitation can result in process termination or, if the attacker can shape the destination, arbitrary code execution within the encoder process.

No public proof-of-concept is referenced in the advisory. The fix is published by AOMedia in commit a93ba0ffaa. Technical details are available in the Red Hat CVE-2026-56209 Advisory, the AOM Media Patch Note, the Red Hat Bug Report #2490800, and Chromium Issue #503993984.

Detection Methods for CVE-2026-56209

Indicators of Compromise

Unexpected crashes, segmentation faults, or SIGSEGV signals in processes linking libaom during AV1 encoding with SVC enabled.
Core dumps showing faulting writes inside cyclic refresh routines or anomalous pointer values originating from SVC layer ID handling.
Encoder processes spawning unexpected child processes or making outbound network connections after processing untrusted media.

Detection Strategies

Inventory all services and applications that statically or dynamically link libaom and confirm whether SVC encoding paths are reachable.
Apply runtime memory safety mitigations (ASLR, CFI, heap hardening) and monitor for violations in media processing workloads.
Hunt for anomalous process behavior in transcoding, WebRTC, and video conferencing services that accept externally supplied frames.

Monitoring Recommendations

Forward crash telemetry and coredump events from media servers to a centralized log platform for correlation.
Alert on repeated encoder restarts or abnormal CPU and memory patterns on hosts running AV1 encoding workloads.
Track package versions of libaom and downstream distributions to detect drift from patched builds.

How to Mitigate CVE-2026-56209

Immediate Actions Required

Update libaom to a build that includes upstream commit a93ba0ffaa or the equivalent vendor backport.
Rebuild and redeploy applications that statically link libaom after upgrading the library.
Restrict which clients can submit frames to network-facing AV1 encoders until patched builds are in place.

Patch Information

The upstream fix is published by AOMedia at commit a93ba0ffaa and adds the missing bounds check in the SVC layer ID control path. Red Hat tracks distribution updates in Red Hat Bug #2490800 and the Red Hat CVE-2026-56209 Advisory. Chromium tracks the downstream impact in Chromium Issue #503993984. Operators should consult their Linux distribution's security tracker for the specific patched package version.

Workarounds

Disable SVC encoding in libaom-based services where the feature is not required.
Place AV1 encoder workloads behind authenticated, trusted-source-only ingestion to limit attacker reach.
Sandbox encoder processes with seccomp, AppArmor, or SELinux profiles to constrain the impact of memory corruption.

bash

# Confirm installed libaom version on RPM-based systems
rpm -q libaom

# On Debian/Ubuntu
dpkg -l | grep libaom

# Update to the patched package (example for RHEL)
sudo dnf update libaom