FFmpeg CVE-2026-64835

Exploitation requires the target to decode an attacker-supplied ADX or AAX audio file through FFmpeg's ADX decoder, and the file must deliver an AV_PKT_DATA_NEW_EXTRADATA side-data block mid-stream that changes the channel layout - this specific mid-stream extradata channel-change is the concrete trigger, not merely a malformed file. No authentication is needed (PR:N), but passive user interaction is required (UI:P): the victim or an automated pipeline must actually feed the file to a vulnerable decode path. Limiting factors are that the application must build and reach the ADX/AAX decoder (not enabled or exercised in all FFmpeg deployments), must be running an affected version (4.4-8.1.2), and must process untrusted input; pipelines that never decode ADX/AAX or that reject side-data channel changes are not exposed.

The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H) describes a network-reachable, low-complexity, unauthenticated flaw that requires passive user interaction - a victim must decode a malicious file - and yields high confidentiality, integrity, and availability impact with no scope change. The realistic risk is elevated by FFmpeg's ubiquity and the memory-write primitive (OOB write is more dangerous than read-only), but tempered by the UI:P requirement and the absence of active-exploitation or POC signals: no CISA KEV listing and no public exploit identified. No EPSS score or SSVC decision was supplied in the input, so automatable/exploitation-maturity signals cannot be weighed. The specific trigger - a mid-stream AV_PKT_DATA_NEW_EXTRADATA channel-layout change on an ADX/AAX stream - is an unusual condition that most simple decode paths will not hit, suggesting the practical exploitation surface is narrower than the raw score implies. Treat as a genuine high-priority patch for anyone decoding untrusted ADX/AAX content, but not an emergency zero-day.

An attacker crafts a malicious ADX or AAX audio file that begins with one channel layout and injects an AV_PKT_DATA_NEW_EXTRADATA side-data block mid-stream declaring a different channel count, then delivers it to a victim (email attachment, download, or an automated transcoding service). When FFmpeg decodes the file, adx_decode_frame re-parses the header without updating channel state and reads/writes the prev[] array out of bounds, causing a crash or potentially memory corruption leading to code execution. No public exploit code has been identified at time of analysis, and successful exploitation requires the victim to process the file (UI:P).