[bug/Fuzzing] Incorrect validation of pre-state attestation & malformed block signature during state transition (nim)

[pventuzelo]

Hi guys,

After fuzzing with beacon-fuzz, we found an issue in prysm and I reported it here:
[bug/fuzzing] Incorrect validation of pre-state attestation & malformed block signature during state transition.

Download: incorrect_ssz_validation_prysm.zip

Based on testing with ./ncli_transition, you also have the same issues:

$ make

$ cd ncli

$ ../env.sh nim c -d:const_preset=mainnet ncli_transition

$ ./ncli_transition --pre= incorrect_ssz_validation_state_prysm.ssz --blck= incorrect_ssz_validation_block_prysm.ssz --post= post.ssz
...
# process continued without any errors

Environment

preset: mainnet preset
branch: devel
commit: fada11e

[tersec]

According to discussion from #955 it's not clear we'll fix this as such. I'll leave this open for now, pending further discussion.