CVE-2026-56209

An arbitrary address write vulnerability was found in libaom, the reference AV1 codec implementation. A missing bounds check in the SVC (Scalable Video Coding) layer ID control function allows an attacker to inject an arbitrary pointer into the cyclic refresh map field via crafted image pixel values. The encoder then writes approximately 1,200 bytes at the attacker-controlled address. This is fully deterministic and does not require a separate information leak. An attacker who can supply frames to a network-facing libaom encoder with SVC enabled could exploit this for denial of service or potential code execution.

This vulnerability is rated as Critical severity because it provides a fully deterministic arbitrary address write primitive that requires no information leak and is self-bootstrapping from attacker-controlled pixel values. The 1,200-byte write at an attacker-chosen address is sufficient for control flow hijacking. In Red Hat products, libaom ships bundled within Firefox and Thunderbird. The vulnerable code path requires the SVC (Scalable Video Coding) encoder feature to be enabled and the attacker to control both the layer_id configuration and the image frame pixel values. In Firefox's WebRTC implementation, SVC encoding parameters and frame submission are managed internally by the browser; a remote peer cannot directly set arbitrary layer IDs or inject pixel values into the local encoder. This significantly reduces exploitability in the browser context. RHEL-AI 3.4 (aom 3.12.0) and Hummingbird 1 (aom 3.13.3) ship standalone libaom packages within the affected version range. Services on those platforms that expose the SVC encoder API with attacker-controlled layer configuration and frame input are at highest risk.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

There is no complete mitigation for this vulnerability. The following measures can reduce risk:

1. If using libaom as a standalone encoder library with SVC enabled, validate that spatial_layer_id and temporal_layer_id values are within the configured range [0, configured_layers) before calling aom_codec_control with AV1E_SET_SVC_LAYER_ID.
2. Restrict access to encoding services to trusted clients only. Do not expose libaom SVC encoder configuration to untrusted input.
3. For Firefox and Thunderbird, ensure browsers are updated to versions that include the patched libaom (v3.14.0 or later).
4. Deploy encoding services with ASLR, stack canaries, and other exploit mitigation technologies enabled.