[crash/fuzzing] DoS/infinite processing during block ssz parsing

[pventuzelo]

Description

During fuzzing with new version (under development) of beacon-fuzz, I found a bug leading to a Denial of Service (DoS) of teku.
More specifically, an "infinite processing" triggered using teku transition blocks.

Based on other eth2 clients errors, bug seems to be an out-of-bound issue not detected during Teku Block SSZ parsing:

• lighthouse: Ssz decode failed: OutOfBoundsByte { i: 0 }
• nim: SszSizeMismatchError

Steps to Reproduce (Bug)

• Download: infinite_process_ssz_teku.zip
• Crash:

# install
./gradlew distTar installDist

# go to build folder
cd build/install/

# Run teku
bin/teku transition blocks --pre=infinite_process_ssz_state_teku.ssz --network=mainnet infinite_process_ssz_block_teku.ssz
# PROCESS NEVER STOP...

Versions

• Github branch: master
• Github commit: 1cc3466
• Java version: openjdk version "11.0.7" 2020-04-14
• OS Name & Version: Ubuntu 18.04.4 LTS
• Kernel Version: 4.15.0-96-generic