High [CVE-2026-56210] heap-buffer-overflow read via missing bounds check in ctrl_set_layer_id

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.