A single-file bundle manifest is attacker-controlled. Opening a compressed
entry pre-allocated a MemoryStream of the declared decompressed size
through an unchecked long-to-int cast, then inflated the whole deflate
stream before comparing lengths. A few-byte payload declaring ~2 GB thus
forced a ~2 GB allocation up front, sizes at or above 2 GB wrapped to a
negative capacity, and a decompression bomb was expanded in full before
the mismatch was noticed (CWE-789, CWE-197).
Grow the buffer only with bytes the deflate stream actually produces and
stop reading one byte past the declared size, which already proves the
entry corrupt. Reject declared sizes that cannot fit a single in-memory
buffer as invalid bundle data. Entry offsets need no extra check: the
UnmanagedMemoryStream over the mapping already validates them against the
view length.
Assisted-by: Claude:claude-fable-5:Claude Code
Christoph Wille
4980c011b8