Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in elixir-grpc grpc (GRPC.Compressor.Gzip, GRPC.Message modules) allows a denial of service via a gzip decompression bomb.

This vulnerability is associated with program files lib/grpc/compressor/gzip.ex, lib/grpc/message.ex and program routines 'Elixir.GRPC.Compressor.Gzip':decompress/1, 'Elixir.GRPC.Message':from_data/2.

'Elixir.GRPC.Compressor.Gzip':decompress/1 calls :zlib.gunzip/1 directly on attacker-controlled bytes with no decompressed-size limit, ratio check, or incremental decoding. Because this module is the registered gzip GRPC.Compressor implementation, it is invoked automatically whenever an incoming gRPC frame carries the grpc-encoding: gzip header. :zlib.gunzip/1 allocates the entire decompressed result as a single binary, so a small highly compressible payload (for example a few kilobytes of zeros, which gzip compresses at roughly 1000:1) expands to multiple gigabytes inside a single call. The max_receive_message_length limit is enforced only against the already-decompressed message, so it provides no protection. An unauthenticated remote peer can send a single crafted frame to exhaust the BEAM node's heap and trigger an out-of-memory kill.

This issue affects grpc: from 0.4.0 before 1.0.0.

Affected: Hex: grpc

### Summary An unauthenticated remote peer can crash any gRPC server built on this library by sending a small gzip-compressed frame that decompresses to gigabytes, exhausting the BEAM node's heap and triggering an OOM kill (denial of service).

Introduced in https://github.com/elixir-grpc/grpc/commit/beae6800fc8baf126f3fe7107d86a50e105275ba

### Details `GRPC.Compressor.Gzip.decompress/1` (lib/grpc/compressor/gzip.ex:12-14) calls `:zlib.gunzip/1` directly on attacker-controlled bytes with no size limit, no ratio check, and no incremental decoding. Because this module is registered as a `GRPC.Compressor` implementation, it is invoked automatically whenever an incoming gRPC frame carries `grpc-encoding: gzip`. `:zlib.gunzip/1` allocates the entire decompressed result as a single binary before returning, so a highly compressible payload (e.g. a few kilobytes of zeros, which gzip compresses at roughly 1000:1) expands to multiple gigabytes inside a single function call. The server's `max_receive_message_length` is enforced only against the already-decompressed message, so it provides no protection here. A single request is sufficient to OOM-kill the node.

### PoC A script that verifies the vulnerability is attached to the end of this report. Run it against a stock gRPC server using this library; the BEAM node's memory usage will balloon and the VM will be OOM-killed after a single request.

### Impact This is a decompression bomb / denial-of-service vulnerability. Any service th…