CVE-2025-47774 Vyper's `slice()` may elide side-effects when output length is 0
Vyper compiler may skip side effects in slice operations with zero length, potentially altering smart contract logic execution.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2025-47774?
CVE-2025-47774 is a low-severity vulnerability in vyperlang vyper, published on 15 May 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Vyper is the Pythonic Programming Language for the Ethereum Virtual Machine. In versions up to and including 0.4.2rc1, the `slice()` builtin can elide side effects when the output length is 0, and the source bytestring is a builtin (`msg.data` or `<address>.code`). The reason is that for these source locations, the check that `length >= 1` is skipped. The result is that a 0-length bytestring constructed with slice can be passed to `make_byte_array_copier`, which elides evaluation of its source argument when the max length is 0. The impact is that side effects in the `start` argument may be elided when the `length` argument is 0, e.g. `slice(msg.data, self.do_side_effect(), 0)`. The fix in pull request 4645 disallows any invocation of `slice()` with length 0, including for the ad hoc locations discussed in this advisory. The fix is expected to be part of version 0.4.2.
Weakness: CWE-691
Which versions are affected by CVE-2025-47774?
3 open source packages ship an affected version, including vyper.
| Package | Affected | Fixed in |
|---|---|---|
vyper PyPI | All versions to 0.4.2rc1 | None |
vyper PyPI | All versions to 0.4.2rc1 | None |
vyper PyPI | All versions to 0.4.2rc1 | None |
How do I fix CVE-2025-47774?
No fix has been published for CVE-2025-47774 yet. Limit exposure of the affected software until one is available.
Is CVE-2025-47774 being exploited?
There is no known exploitation of CVE-2025-47774 in the wild and no public exploit code.
Sources
Also known as GHSA-3vcg-j39x-cwfm, PYSEC-2026-2028.