Sign in
Deutsch English Español Polski
Low

VVE-2021-0002: Incorrect `returndatasize` when using simple forwarder proxies deployed prior to EIP-1167 adoption

  • Disclosed: 19.04.2021
  • Updated: 11.10.2026 12:18

Background

@tjayrush reported a data handling issue with certain Web3 libraries using Vyper-deploy forwarder proxy contracts using our Vyper's built-in create_forwarder_to function prior to our change to support EIP-1167 style forwarder proxies.

Impact

If you are an end user of a forwarder-style proxy deployed using Vyper's built-in create_forwarder_to function AND you have a function that returns >4096 bytes AND you do no return data sanitation on the value returned, you could potentially see a data corruption issue.

Otherwise, if you are handling the result of a return call AND you expect a specific RETURNDATASIZE that is less than 4096 (such as SafeERC20.safeTransfer) then the call will fail that check.

Patches

The issue was patched when we upgraded to EIP-1167 style forwarder proxies in #2281.

Workarounds

If you are making a call to a contract method that is expected to return <= 4096 bytes, there is no issue as the ABI decoders in both Solidity and Vyper will truncate the data properly. Web3 libraries will also do this, unless you are doing eth_call or eth_sendTransaction directly.

If you are using a Solidity library that checks RETURNDATASIZE of an external call to a forwarder proxy deployed prior to this patch, it will fail on that assertion (such as SafeERC20.safeTransfer). The workaround is to always do a greater than or equal to check, rather than a strict equals to check.

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Python (PyPI) vyper < 0.2.9 0.2.9

References

CVSS score -
Weakness (CWE)
CWE-20
Platform
Python (PyPI)
Package
vyper
Disclosed
19.04.2021
Updated
11.10.2026 12:18

Sources and licenses

OSV / GitHub Advisory Database - GHSA-375m-5fvv-xq23 - CC BY 4.0

Vulnerability history: vyper

All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (47) in the archive
Total entries
47
First → latest
03.2020 10.2026
Without a fix
5
Exploited in attacks
0

Severity breakdown

  • Critical 3
  • High 14
  • Medium 20
  • Low 10

Disclosures per year

Severity:
  1. Vyper negative array index bounds checks
    Critical · 9.8 CVE-2024-24563 < 0.4.0 0.4.0
  2. Vyper's bounds check on built-in `slice()` function can be overflowed
    Critical · 9.8 CVE-2024-24561 < 0.4.0 0.4.0
  3. concat built-in can corrupt memory in vyper
    High · 7.3 CVE-2024-22419 >= 0.3.0, < 0.4.0 0.4.0
  4. incorrect storage layout for contracts containing large arrays
    High · 7.5 CVE-2023-46247 < 0.3.8 0.3.8
  5. Vyper vulnerable to memory corruption in certain builtins utilizing `msize`
    High · 8.1 CVE-2023-42443 >= 0.3.4, < 0.3.10 0.3.10
  6. Vyper has incorrectly allocated named re-entrancy locks
    Critical · 8.7 CVE-2023-39363 >= 0.2.15, < 0.3.1 0.3.1
  7. Vyper vulnerable to incorrect ordering of arguments for kwargs passed to internal calls
    High · 7.5 CVE-2023-32059 < 0.3.8 0.3.8
  8. Vyper vulnerable to integer overflow in loop
    High · 7.5 CVE-2023-32058 < 0.3.8 0.3.8
  9. Vyper vulnerable to OOB DynArray access when array is on both LHS and RHS of an assignment
    High · 7.5 CVE-2023-31146 < 0.3.8 0.3.8
  10. vyper vulnerable to storage allocator overflow
    High · 7.5 CVE-2023-30837 < 0.3.8 0.3.8
  11. Incorrect success value returned in vyper
    High · 7.5 CVE-2023-30629 >= 0.3.1, < 0.3.8 0.3.8
  12. Multiple evaluation of contract address in call in vyper
    High · 7.5 CVE-2022-29255 < 0.3.4 0.3.4
  13. Vyper is a pythonic Smart Contract Language for the ethereum virtual machine. In affected versions, the return of `<iface>.returns_int128()` is not validated to fall within the bounds of `int128`. Thi
    High · 8.8 CVE-2022-24845 < 0.3.2 0.3.2
  14. Buffer Overflow in vyper
    High · 7.1 CVE-2022-24788 < 0.3.2 0.3.2
  15. Incorrect Comparison in Vyper
    High · 7.5 CVE-2022-24787 < 0.3.2 0.3.2
  16. Memory corruption when returning a literal struct with a private call inside of it
    High · 7.5 CVE-2021-41121 < 0.3.0 0.3.0
  17. Storage corruption due to variables overwritten by re-entrancy locks
    High ghsa-7f92-rr6w-cq64 >= 0.2.13, < 0.2.15 0.2.15
  18. VVE-2021-0002: Incorrect `returndatasize` when using simple forwarder proxies deployed prior to EIP-1167 adoption this entry
    Low ghsa-375m-5fvv-xq23 < 0.2.9 0.2.9

Know which vulnerabilities affect your application

With the DockRay integration and software inventory enabled, DockRay checks reported component versions against known vulnerabilities and notifies you about confirmed matches. Coverage depends on the supported technology and available advisory data.

Connect your application
DockRay newsletter

Application security in your inbox

Important vulnerabilities, actionable guidance and practical advice for your applications. Choose your technologies and follow what matters to your project.

  • A daily digest of new vulnerabilities, critical ones included.
  • Notifications about important updates.
  • Practical advice on application security and monitoring.

Leave empty to receive updates for every technology.

Privacy policy

Free to subscribe. Unsubscribe with one click in any email.