CVE-2025-27104 double eval in For List Iter in Vyper

What is CVE-2025-27104?

CVE-2025-27104 is a low-severity vulnerability in vyperlang vyper, published on 21 Feb 2025. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

vyper is a Pythonic Smart Contract Language for the EVM. Multiple evaluation of a single expression is possible in the iterator target of a for loop. While the iterator expression cannot produce multiple writes, it can consume side effects produced in the loop body (e.g. read a storage variable updated in the loop body) and thus lead to unexpected program behavior. Specifically, reads in iterators which contain an ifexp (e.g. `for s: uint256 in ([read(), read()] if True else [])`) may interleave reads with writes in the loop body. Vyper for loops allow two kinds of iterator targets, namely the `range()` builtin and an iterable type, like SArray and DArray. During codegen, iterable lists are required to not produce any side-effects (in the following code, `range_scope` forces `iter_list` to be parsed in a constant context, which is checked against `is_constant`). However, this does not prevent the iterator from consuming side effects provided by the body of the loop. For SArrays on the other hand, `iter_list` is instantiated in the body of a `repeat` ir, so it can be evaluated several times. This issue is being addressed and is expected to be available in version 0.4.1. Users are advised to upgrade as soon as the patched release is available. There are no known workarounds for this vulnerability.

Weakness: CWE-662

Which versions are affected by CVE-2025-27104?

3 open source packages ship an affected version, including vyper. It affects 1 product.

Products include Vyperlang Vyper.

How do I fix CVE-2025-27104?

Upgrade vyper to 0.4.1 or later.

Is CVE-2025-27104 being exploited?

There is no known exploitation of CVE-2025-27104 in the wild and no public exploit code.

Other vulnerabilities in vyperlang vyper

• CVE-2024-24563 Vyper array negative index vulnerability Critical 9.8
• CVE-2024-24561 Vyper bounds check on built-in `slice()` function can be overflowed Critical 9.8
• CVE-2023-39363 Vyper incorrectly allocated named re-entrancy locks Critical 9.1
• CVE-2022-24845 Integer bounds error in Vyper High 8.8
• CVE-2022-29255 Multiple evaluation of contract address in call in vyper High 8.2

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-h33q-mhmp-8p67, PYSEC-2025-30.