CVE-2026-56210

A heap-buffer-overflow read 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 setting a spatial_layer_id exceeding the configured number of layers. This causes an out-of-bounds heap read of approximately 40,728 bytes when computing a layer context array index. An attacker who can influence SVC encoder parameters in a network-facing service could exploit this for information disclosure (heap content leak) or denial of service (segmentation fault from hitting unmapped memory).

This vulnerability is rated as Important severity because the 40KB out-of-bounds heap read can disclose sensitive information from adjacent heap allocations (including pointers useful for ASLR bypass in chained attacks) and reliably causes denial of service by hitting unmapped pages. In Red Hat products, libaom ships bundled within Firefox and Thunderbird. The vulnerable code path requires the SVC encoder feature to be enabled and an attacker to set spatial_layer_id to a value exceeding the number of configured spatial layers. In Firefox's WebRTC implementation, SVC layer parameters are managed internally by the browser and not directly exposed to remote peers, which limits exploitability. 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 that expose SVC encoder layer configuration to untrusted input are affected.

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 does not exceed the number of configured spatial layers before calling aom_codec_control with AV1E_SET_SVC_LAYER_ID.
2. Restrict access to encoding services to trusted clients only.
3. For Firefox and Thunderbird, ensure browsers are updated to versions that include the patched libaom (v3.14.0 or later).
4. Monitor encoding service processes for unexpected crashes (segfaults) that may indicate exploitation attempts.