The vulnerability is an uninitialized memory disclosure. The function adpcm_encode_frame() leaks heap bytes when encoding mono ADPCM_MS audio with trellis enabled. Attackers providing audio data can receive output packets that contain approximately half of each block filled with stale heap memory from the encoding process. This may expose sensitive information stored in memory, leading to confidentiality compromise. The weakness is identified as CWE‑908 due to exposed uninitialized data.

FFmpeg releases up to and including version 9.0.2 are affected. The issue originates in libavcodec/adpcmenc.c and impacts all systems running FFmpeg 9.0.2 or earlier when the ADPCM_MS trellis encoder is used. Users who employ FFmpeg in services or applications should verify whether their deployments satisfy this version constraint.

The CVSS base score of 2.0 reflects a low-impact information disclosure with no impact on integrity or availability. No EPSS data is available, and the vulnerability is not currently listed in CISA’s KEV catalog, suggesting limited or low exploitation likelihood. However, the attack requires the ability to submit audio for encoding and to receive the encoded output. The likely attack vector is remote or local input of audio data to a vulnerable service or application; it is inferred from the description that the attacker must control the input stream. If the application exposes the encoder to untrusted inputs, the disclosure could leak heap data that may contain secrets, although it does not allow arbitrary code execution.