GHSA-ppx5-q359-pvwj
GitHub Security Advisory
vyper's range(start, start + N) reverts for negative numbers
Advisory Details
### Summary
When looping over a `range` of the form `range(start, start + N)`, if `start` is negative, the execution will always revert.
### Details
This issue is caused by an incorrect assertion inserted by the code generation of the range (`stmt.parse_For_range()`):
https://github.com/vyperlang/vyper/blob/9136169468f317a53b4e7448389aa315f90b95ba/vyper/codegen/stmt.py#L286-L287
This assertion was introduced in https://github.com/vyperlang/vyper/commit/3de1415ee77a9244eb04bdb695e249d3ec9ed868 to fix https://github.com/advisories/GHSA-6r8q-pfpv-7cgj. The issue arises when `start` is signed, instead of using `sle`, `le` is used and `start` is interpreted as an unsigned integer for the comparison. If it is a negative number, its 255th bit is set to `1` and is hence interpreted as a very large unsigned integer making the assertion always fail.
### PoC
```Vyper
@external
def foo():
x:int256 = min_value(int256)
# revert when it should not since we have the following assertion that fails:
# [assert, [le, min_value(int256), max_value(int256) + 1 - 10]],
for i in range(x, x + 10):
pass
```
### Patches
patched in v0.4.0, specifically, https://github.com/vyperlang/vyper/pull/3679 disallows this form of `range()`.
### Impact
Any contract having a `range(start, start + N)` where `start` is a signed integer with the possibility for `start` to be negative is affected. If a call goes through the loop while supplying a negative `start` the execution will revert.
Affected Packages
Related CVEs
Key Information
Dataset
Data from GitHub Advisory Database. This information is provided for research and educational purposes.