# CVE-2024-38365 public disclosure (btcd \`FindAndDelete\` bug)

**URL:** <https://delvingbitcoin.org/t/cve-2024-38365-public-disclosure-btcd-findanddelete-bug/1184>\
**Category:** Implementation\
**Tags:** announcement\
**Created:** [October 10, 2024, 9:02am UTC](https://delvingbitcoin.org/t/cve-2024-38365-public-disclosure-btcd-findanddelete-bug/1184 "2024-10-10T09:02:17Z")\
**Posts on this page:** 1\
**Showing post:** 9

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**Author:** ![AntoineP](https://delvingbitcoin.org/user_avatar/delvingbitcoin.org/antoinep/32/483_2.png) [@AntoineP](https://delvingbitcoin.org/u/AntoineP)\
**Post date:** [October 15, 2024, 1:09pm UTC](https://delvingbitcoin.org/t/cve-2024-38365-public-disclosure-btcd-findanddelete-bug/1184/9 "2024-10-15T13:09:04Z")

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> [@ariard](#):
>
> Though there is still the possibility that the signature is invalid w.r.t the `scriptCode` and the script execution still valid.

Sure, but what we want here is a different script execution between btcd and Core. In the context of this disclosure, this was only possible using a discrepancy in the `FindAndDelete` implementation therefore you need a signature to be found in the `scriptCode`. Further, you need the signature to be valid for either btcd or Core, which is only possible if you do public key recovery.

> [@ariard](#):
>
> What if you have : \<invalid\_sig+noise\> \<invalid\_sig\> \<OP\_CHECKSIG\> \<OP\_SIZE\> \<length\_invalid\_sig+noise\> OP\_EQUALVERIFY.
> 
> In my understanding, core’ should only remove 1 instance of \<invalid\_sig\>, fails on the CHECKSIG (though `NULLFAIL` policy only) and then succeed on the OP\_SIZE. On the other hand, non-upgraded btcd should remove the 2 instances of \<invalid\_sig\> (as invalid\_sig+noise contains the invalid\_sig) and fails the OP\_SIZE + OP\_EQUALVERIFY.

I’m not sure what you are trying to get at since your Script is different from what i think you meant:

- Here the `CHECKSIG` would be executed taking `<invalid_sig+noise>` as signature and `<invalid_sig>` as public key, which is always going to push 0 on the stack;
- `OP_SIZE` would then be executed on the result of the `CHECKSIG`, which is always 0, and so would always return 0 as well;
- Then `OP_EQUALVERIFY` would always fail since the length of the invalid sig + noise would never be 0.

I assume you mean that running OP\_CHECKSIG would drop the `<invalid_sig>` (in Bitcoin Core), or both `<invalid_sig>` and `<invalid_sig + noise>`, from the Script itself and lead to a discrepancy of the execution when asserting the size of the top element left on the stack. Then you are misunderstanding what `FindAndDelete` does. It does not tamper with the Script being executed at all, it only modifies a copy of it for the purpose of committing to it in the sighash. Even if your Script from above correctly implemented what i think you intended it to, it would not cause a different execution between btcd and Bitcoin Core: the executed script is always the same so the size of the top stack element would always be the same for both.

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_[View the full topic](https://delvingbitcoin.org/t/cve-2024-38365-public-disclosure-btcd-findanddelete-bug/1184)._