Vyper has a double eval in For List Iter

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

2.3 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2025-27104: 0.45% estimated exploitation activity in the next 30 days; percentile 38.89 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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. The fix is tracked in https://github.com/vyperlang/vyper/pull/4488. Vulnerability Details 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, rangescope forces iterlist to be parsed in a constant context, which is checked against isconstant). However, this does not prevent the iterator from consuming side effects provided by the body of the…

Published by the source

21 Feb 2025, 22:43 UTC

Last modified by the source

9 Apr 2025, 20:36 UTC

Source last checked

26 Oct 2026, 13:31 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-h33q-mhmp-8p67

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-h33q-mhmp-8p67

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# Patch Next advisory brief: CVE-2025-27104

Advisory: Vyper has a double eval in For List Iter
IDs: CVE-2025-27104, GHSA-h33q-mhmp-8p67
Record: https://patchnext.com/advisories/cve-2025-27104 (revision 3, source checked 26 Oct 2026, 13:31 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: vyper 0.4.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI vyper: affected <= 0.4.0; fixed in 0.4.1

## Suggested inspection (read-only)
- `python -m pip show vyper`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on vyper.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-h33q-mhmp-8p67 (OSV record GHSA-h33q-mhmp-8p67 lists affected ranges: PyPI vyper >=0 <0.4.1 (fixed))
- Verified: https://github.com/advisories/GHSA-h33q-mhmp-8p67 (GitHub-reviewed advisory GHSA-h33q-mhmp-8p67 lists affected ranges: PyPI vyper >=0 <=0.4.0)

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