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Vikhyath Mondreti
d4195ff682
`convert` and `extract_audio` built their output path as
`path.join(dir, `out.${format}`)`, and `format` arrives from the tool as an
unconstrained `{type: 'string'}` — no pattern, no enum, and the handler passes it
through untouched. A format of `../../../../../../../../tmp/x.mp4` resolves to
`/tmp/x.mp4`, so FFmpeg writes attacker-influenced media wherever the traversal
points. Verified against a real binary: the run produced a 44,078-byte MP4
outside the temp directory, which the `rm -rf` cleanup then never saw, because
the file was never inside the directory being removed.
Output extensions are now letters and digits only. The pattern admits no `.` and
no separator, so `out.${ext}` is always a single path segment and containment
follows from the validation itself rather than from a second check that could
drift away from it.
`trim` and `fade` build their paths from `extFromMime`, which returns
`mime.split('/')[1]` — that can never contain a separator, so those stay inside
the temp dir and keep accepting values like `x-msvideo` that this stricter
pattern would wrongly reject.