Deserialization of Untrusted Data and Allocation of Resources Without Limits or Throttling vulnerabilities in elixir-grpc grpc allow unauthenticated attackers to crash the BEAM node via atom table exhaustion and, when a decoded term flows into a call site that invokes it, achieve remote code execution on the server.

'Elixir.GRPC.Codec.Erlpack':decode/2 (lib/grpc/codec/erlpack.ex) calls :erlang.binary_to_term/1 on the raw gRPC message body without the :safe option, no size bound, and no type guard. Any unauthenticated peer that sends a request with Content-Type: application/grpc+erlpack can send a crafted payload that mints arbitrary new atoms (which are never garbage-collected, exhausting the bounded atom table and crashing the VM) or that encodes a fun term which, if applied anywhere downstream, executes attacker-controlled code inside the server process.

This issue affects grpc: from 0.4.0 before 1.0.0.

Affected: Hex: grpc

### Summary

`GRPC.Codec.Erlpack.decode/2` calls `:erlang.binary_to_term/1` directly on the raw gRPC message body without the `:safe` option. Any unauthenticated peer that can reach a gRPC endpoint with `Content-Type: application/grpc+erlpack` can crash the entire BEAM node via atom table exhaustion or, if a decoded fun term flows into a call site that invokes it, achieve remote code execution inside the server process.

### Details

**Root cause** — `lib/grpc/codec/erlpack.ex` implements `decode/2` as a bare `:erlang.binary_to_term(binary)` call with no `:safe` flag, no size limit, and no type validation. This has two independent exploitation paths:

**1. DoS via atom exhaustion** — BEAM atoms are never garbage-collected and the global atom table is bounded (~1,048,576 entries). A crafted payload encoding large numbers of fresh atoms saturates the table and crashes the entire VM, taking down all applications on the node.

**2. RCE via fun materialization** — Without `:safe`, `binary_to_term/1` reconstructs fun and external-fun terms from wire data. If the decoded value reaches any call site that applies it (e.g. `Enum.map`, `Task.async`, direct invocation), attacker-controlled code executes inside the server process.

**Configuration requirement:** `GRPC.Codec.Erlpack` is not registered by default and must be explicitly added to the server's `codecs` option.

### PoC

1. Start a gRPC server with `codecs: [GRPC.Codec.Erlpack]`. 2. Open an HTTP/2 connection to the server. 3.…

Affected: Ubuntu:16.04:LTS: grpc, Ubuntu:18.04:LTS: grpc, Ubuntu:20.04:LTS: grpc, Ubuntu:22.04:LTS: grpc, Ubuntu:24.04:LTS: grpc, Ubuntu:25.10: grpc, Ubuntu:26.04:LTS: grpc

Deserialization of Untrusted Data and Allocation of Resources Without Limits or Throttling vulnerabilities in elixir-grpc grpc allow unauthenticated attackers to crash the BEAM node via atom table exhaustion and, when a decoded term flows into a call site that invokes it, achieve remote code execution on the server. 'Elixir.GRPC.Codec.Erlpack':decode/2 (lib/grpc/codec/erlpack.ex) calls :erlang.binary_to_term/1 on the raw gRPC message body without the :safe option, no size bound, and no type guard. Any unauthenticated peer that sends a request with Content-Type: application/grpc+erlpack can send a crafted payload that mints arbitrary new atoms (which are never garbage-collected, exhausting the bounded atom table and crashing the VM) or that encodes a fun term which, if applied anywhere downstream, executes attacker-controlled code inside the server process. This issue affects grpc: from 0.4.0 before 1.0.0.