Headline
CVE-2023-32058: Integer overflow for loops of form `for i in range(x, x+N)`
Vyper is a Pythonic smart contract language for the Ethereum virtual machine. Prior to version 0.3.8, due to missing overflow check for loop variables, by assigning the iterator of a loop to a variable, it is possible to overflow the type of the latter. The issue seems to happen only in loops of type for i in range(a, a + N)
as in loops of type for i in range(start, stop)
and for i in range(stop)
, the compiler is able to raise a TypeMismatch
when trying to overflow the variable. The problem has been patched in version 0.3.8.
Impact
Due to missing overflow check for loop variables, by assigning the iterator of a loop to a variable, it is possible to overflow the type of the latter.
In the following example, calling test returns 354, meaning that the variable a did store 354 a value out of bound for the type uint8.
@external def test() -> uint16: x:uint8 = 255 a:uint8 = 0 for i in range(x, x+100): a = i return convert(a,uint16)
The issue seems to happen only in loops of type for i in range(a, a + N) as in loops of type for i in range(start, stop) and for i in range(stop), the compiler is able to raise a TypeMismatch when trying to overflow the variable.
thanks to @trocher for reporting
Patches
The problem has currently not been patched.
Workarounds
Related news
### Impact Due to missing overflow check for loop variables, by assigning the iterator of a loop to a variable, it is possible to overflow the type of the latter. In the following example, calling `test` returns `354`, meaning that the variable `a` did store `354` a value out of bound for the type `uint8`. ```Vyper @external def test() -> uint16: x:uint8 = 255 a:uint8 = 0 for i in range(x, x+100): a = i return convert(a,uint16) ``` The issue seems to happen only in loops of type `for i in range(a, a + N)` as in loops of type `for i in range(start, stop)` and `for i in range(stop)`, the compiler is able to raise a `TypeMismatch` when trying to overflow the variable. thanks to @trocher for reporting ### Patches The problem is patched at https://github.com/vyperlang/vyper/commit/3de1415ee77a9244eb04bdb695e249d3ec9ed868 ### Workarounds