Vyper's external calls can overflow return data to return input buffer

Exploitation

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

CVSS

3.7 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS

• CVE-2024-24560: 0.53% estimated exploitation activity in the next 30 days; percentile 44.60 (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.

Summary When calls to external contracts are made, we write the input buffer starting at byte 28, and allocate the return buffer to start at byte 0 (overlapping with the input buffer). When checking RETURNDATASIZE for dynamic types, the size is compared only to the minimum allowed size for that type, and not to the returned value's length. As a result, malformed return data can cause the contract to mistake data from the input buffer for returndata. This advisory is given a severity of "Low" because when the called contract returns invalid ABIv2 encoded data, the calling contract can read different invalid data (from the dirty buffer) than the called contract returned. Details When arguments are packed for an external call, we create a buffer of size max(args, returndata) + 32. The input buffer is placed in this buffer (starting at byte 28), and the return buffer is allocated to start at byte 0. The assumption is that we can reuse the memory becase we will not be able to read past…

Published by the source

2 Feb 2024, 18:10 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:27 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-gp3w-2v2m-p686

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-gp3w-2v2m-p686

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# Patch Next advisory brief: CVE-2024-24560

Advisory: Vyper's external calls can overflow return data to return input buffer
IDs: CVE-2024-24560, GHSA-gp3w-2v2m-p686
Record: https://patchnext.com/advisories/cve-2024-24560 (revision 2, source checked 26 Oct 2026, 13:27 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 3.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: vyper 0.4.0. A vendor fix does not mean a deployment is fixed.

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

## 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-gp3w-2v2m-p686 (OSV record GHSA-gp3w-2v2m-p686 lists affected ranges: PyPI vyper >=0 <0.4.0 (fixed))
- Verified: https://github.com/advisories/GHSA-gp3w-2v2m-p686 (GitHub-reviewed advisory GHSA-gp3w-2v2m-p686 lists affected ranges: PyPI vyper >=0 <0.4.0)

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