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GHSA-g2xh-c426-v8mf

GitHub Security Advisory

Vyper: reversed order of side effects for some operations

✓ GitHub Reviewed MODERATE Has CVE

Advisory Details

### Impact

For the following (probably non-exhaustive) list of expressions, the compiler evaluates the arguments from right to left instead of left to right.

```
- unsafe_add
- unsafe_sub
- unsafe_mul
- unsafe_div
- pow_mod256
- |, &, ^ (bitwise operators)
- bitwise_or (deprecated)
- bitwise_and (deprecated)
- bitwise_xor (deprecated)
- raw_call
- <, >, <=, >=, ==, !=
- in, not in (when lhs and rhs are enums)
```

This behaviour becomes a problem when the evaluation of one of the arguments produces side effects that other arguments depend on. The following expressions can produce side-effect:

- state modifying external call
- state modifying internal call
- `raw_call`
- `pop()` when used on a Dynamic Array stored in the storage
- `create_minimal_proxy_to`
- `create_copy_of`
- `create_from_blueprint`

For example:

```Vyper
f:uint256

@internal
def side_effect() -> uint256:
self.f = 12
return 1

@external
def foo() -> uint256:
return unsafe_add(self.f,self.side_effect()) # returns 13 instead of 1
```

```Vyper
a:DynArray[uint256, 12]
@external
def bar() -> bool:
self.a = [1,2,3]
return len(self.a) == self.a.pop() # return false instead of true
```

### Patches
not yet patched, will address in a future release. tracking in https://github.com/vyperlang/vyper/issues/3604.

### Workarounds

When using expressions from the list above, make sure that the arguments of the expression do not produce side effects or, if one does, that no other argument is dependent on those side effects.

### References
_Are there any links users can visit to find out more?_

Affected Packages

PyPI vyper
Affected versions: 0 (last affected: 0.4.2)

Related CVEs

Key Information

GHSA ID
GHSA-g2xh-c426-v8mf
Published
September 4, 2023 4:39 PM
Last Modified
June 18, 2025 5:43 PM
CVSS Score
5.0 /10
Primary Ecosystem
PyPI
Primary Package
vyper
GitHub Reviewed
✓ Yes

Dataset

Last updated: September 16, 2025 6:29 AM

Data from GitHub Advisory Database. This information is provided for research and educational purposes.