Vyper up to 0.4.2rc1 concat insufficient control flow management

Summaryinfo

A vulnerability identified as problematic has been detected in Vyper up to 0.4.2rc1. This issue affects the function concat. This manipulation causes insufficient control flow management. This vulnerability is registered as CVE-2025-47285. Remote exploitation of the attack is possible. No exploit is available. To fix this issue, it is recommended to deploy a patch.

Detailsinfo

A vulnerability classified as problematic was found in Vyper up to 0.4.2rc1. Affected by this vulnerability is the function concat. The manipulation with an unknown input leads to a insufficient control flow management vulnerability. The CWE definition for the vulnerability is CWE-691. The code does not sufficiently manage its control flow during execution, creating conditions in which the control flow can be modified in unexpected ways. As an impact it is known to affect integrity. The summary by CVE is:

Vyper is the Pythonic Programming Language for the Ethereum Virtual Machine. In versions up to and including 0.4.2rc1, `concat()` may skip evaluation of side effects when the length of an argument is zero. This is due to a fastpath in the implementation which skips evaluation of argument expressions when their length is zero. In practice, it would be very unusual in user code to construct zero-length bytestrings using an expression with side-effects, since zero-length bytestrings are typically constructed with the empty literal `b""`; the only way to construct an empty bytestring which has side effects would be with the ternary operator introduced in v0.3.8, e.g. `b"" if self.do_some_side_effect() else b""`. The fix is available in pull request 4644 and expected to be part of the 0.4.2 release. As a workaround, don't have side effects in expressions which construct zero-length bytestrings.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2025-47285 since 05/05/2025. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit.

It is declared as proof-of-concept.

Applying a patch is able to eliminate this problem. The bugfix is ready for download at github.com.

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Name

• Vyper

Version

• 0.4.2rc1

CPE 2.3info

• 🔍

CPE 2.2info

• 🔍

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