The newest version 0.4.25 release of Solidity fixes
two vital bugs.
One other vital bug has already been mounted in model 0.4.22 but it surely was solely found not too long ago that the bug existed.
Word that the Ethereum Basis runs a bounty program for the code generator a part of Solidity.
Cleanup of Exponent in Exponentiation
- Chance of incidence: very low
- Exploitability: excessive
- Discoverability by exams: low
- Mounted in model: 0.4.25
Abstract: Utilizing brief sorts within the exponent of an exponentiation operation can result in invalid outcomes.
The Solidity language permits integer sorts which are shorter than 256 bits, regardless that the Ethereum Digital Machine
solely is aware of kinds of precisely 256 bits. Due to that, greater order bits have to be set to zero every so often.
For a lot of operations, it isn’t related whether or not these bits are set to zero or not (addition is one instance).
Due to that, the Solidity compiler delays this cleanup till it’s wanted with a purpose to save fuel.
Within the very particular circumstance that the exponent of the ** operator has a sort that’s shorter
than 256 bits, however not shorter than the kind of the bottom and comprises soiled greater order bits,
this could result in an incorrect outcome. Word that literal exponents like in x ** 2 in addition to
the case the place the kind of the bottom is uint256 or int256 are unaffected.
Word {that a} perform parameter can have soiled greater order bits if referred to as by a malicious entity,
and the identical is true for information returned from capabilities of contracts deployed by malicious entities.
After having screened numerous contracts, we deem this bug to have an effect on solely a really tiny variety of
good contracts, if any in any respect, as a result of the common makes use of of the exponentiation operator don’t result in the bug.
This bug was discovered by nweller.
Reminiscence Corruption in Multi-Dimensional Array Decoder
- Chance of incidence: low
- Exploitability: medium
- Discoverability by exams: excessive
- Launched in model: 0.1.4
- Mounted in model: 0.4.22
Abstract: Calling capabilities of different contracts that return multi-dimensional fixed-size arrays ends in reminiscence corruption.
If Solidity code calls a perform that returns a multi-dimensional fixed-size array,
the returned ABI-encoded information needs to be transformed to Solidity’s inner illustration
of arrays. In Solidity, multi-dimensional arrays are applied as arrays of
reminiscence pointers, whereas within the ABI, the information is encoded inline.
The decoder didn’t take this distinction into consideration with the outcome that the returned
components are interpreted as reminiscence pointers and thus may cause reminiscence
corruption if the return values are accessed. Calling capabilities with multi-dimensional
fixed-size array arguments is unaffected as is returning fixed-size arrays from perform calls
if they aren’t utilized in a Solidity contract.
The bug is just within the part that decodes a multi-dimensional fixed-size array
that’s returned from a perform name from Solidity.
This bug was discovered by jmahhh.
Invalid Encoding of Structs in Occasions
- Chance of incidence: low
- Exploitability: low
- Discoverability by exams: excessive
- Launched in model: 0.4.17
- Mounted in model: 0.4.25
Abstract: Structs as occasion parameters will not be dealt with correctly.
Structs weren’t meant to be supported as occasion parameters with out the brand new ABI encoder.
The compiler did settle for them however, however encoded their reminiscence handle as an alternative of their precise worth.
Even with the brand new ABI encoder, structs can’t be listed occasion parameters.
Now, structs are correctly disallowed for the previous encoder and if they’re listed additionally for the brand new encoder.
