snappy-java: Unbounded memory allocation from attacker-declared uncompressed lengtha

Impact

Several decompression paths in snappy-java allocate an output buffer sized by the uncompressed length declared in the first bytes of the compressed data, before decompressing or validating it. A few bytes of crafted input can therefore force an allocation of up to 2 GB, causing OutOfMemoryError (denial of service), or a NegativeArraySizeException for declared lengths of 2^31 or more.

Affected entry points include Snappy.uncompress(byte[]), Snappy.uncompressString, the Snappy.uncompress*Array methods, SnappyInputStream, and SnappyFramedInputStream. The maxChunkSize limit added for CVE-2023-43642 bounds only the compressed chunk length, so it does not prevent this.

Patches

Fixed in 1.1.10.9 (#739). Snappy.uncompressedLength() now rejects negative declared lengths, and lengths larger than any valid Snappy stream of the given size can produce. The densest Snappy element expands 3 bytes to 64, so the limit is 64/3 of the compressed size. Allocations are therefore proportional to the input actually received.

Workarounds

Before decompressing untrusted data, check that Snappy.uncompressedLength(input) is within an application-specific limit.