CVE-2025-47285: Vyper Vyper's `concat()` Builtin May Elide Vulnerability

LOW
Advisory Identifier: GHSA-qhr6-mgqr-mchm
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CWE-691
Published
Advisory Summary

CVE-2025-47285 is a LOW vyper's `concat()` builtin may elide vulnerability (CWE-691: Insufficient Control Flow Management) affecting Vyper libraries in the PyPI ecosystem. The issue involves vyper's `concat()` builtin may elide side-effects for zero-length arguments. Remediation is available in the latest vendor maintenance releases.

CVE-2025-47285 at a Glance

CVE Identifier CVE-2025-47285
GHSA Identifier GHSA-qhr6-mgqr-mchm
Severity LOW
CVSS v3.1 Base Score N/A
CWE Classification CWE-691: Insufficient Control Flow Management
Affected Product Vyper
Package Ecosystem PyPI
Published Date
Last Updated

How to Fix CVE-2025-47285

To remediate this vulnerability, upgrade all affected Vyper dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

vyper fixed: Latest secure release 
pip install vyper>=Latest secure release
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show vyper

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2025-47285, inspect your installed packages using pip:

pip show vyper

Analyze the terminal output to locate any version of Vyper in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The pip show vyper command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-691: Insufficient Control Flow Management, where the code does not sufficiently manage its control flow during execution, creating conditions in which the control flow can be modified in unexpected ways. In Vyper, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact `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: https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L560-L562 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 following example demonstrates how the issue would look in user code ```vyper counter: public(uint256) @external def test() -> Bytes[256]: a: Bytes[256] = concat(b"" if self.sideeffect() else b"", b"aaaa") return a def sideeffect() -> bool: self.counter += 1 return True ``` the severity assigned is low, since, as mentioned, this would be a very unusual pattern in user-code. ### Patches fix is tracked in https://github.com/vyperlang/vyper/pull/4644 ### Workarounds don't have side effects in expressions which construct zero-length bytestrings. ### References _Are there any links users can visit to find out more?_

CVE-2025-47285 Affected Vyper Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
vyper
pypi/vyper
PyPI
≤ 0.4.2rc1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/vyperlang/vyper/security/advisories/GHSA-qhr6-mgqr-mchm
NVD — CVE-2025-47285 NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-47285
Vyper Source Repository REPOSITORY
https://github.com/vyperlang/vyper/pull/4644
Vyper Source Repository REPOSITORY
https://github.com/vyperlang/vyper
Vyper Source Repository REPOSITORY
https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L560-L562

Frequently Asked Questions

What is CVE-2025-47285?
CVE-2025-47285 is a security vulnerability in Vyper involving Vyper's `concat()` builtin may elide side-effects for zero-length arguments under CWE-691: Insufficient Control Flow Management.
Which Vyper versions are affected?
Affected versions include releases prior to current release patches across affected packages: vyper.
What version fixes CVE-2025-47285?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is vyper affected?
Yes, vyper is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
What CWE is associated with CVE-2025-47285?
CVE-2025-47285 is classified under CWE-691: Insufficient Control Flow Management (The code does not sufficiently manage its control flow during execution, creating conditions in which the control flow can be modified in unexpected ways.).
How can I check PyPI dependencies for CVE-2025-47285?
Run the dependency tree command: 'pip show vyper'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-qhr6-mgqr-mchm",
  "modified" : "2025-05-16T14:10:25Z",
  "published" : "2025-05-16T14:10:25Z",
  "aliases" : [ "CVE-2025-47285" ],
  "summary" : "Vyper's `concat()` builtin may elide side-effects for zero-length arguments",
  "details" : "### Impact\n`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:\nhttps://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L560-L562\n\nin 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\"\"`.\n\nthe following example demonstrates how the issue would look in user code\n```vyper\ncounter: public(uint256)\n\n@external\ndef test() -> Bytes[256]:\n    a: Bytes[256] = concat(b\"\" if self.sideeffect() else b\"\", b\"aaaa\")\n    return a\n\ndef sideeffect() -> bool:\n    self.counter += 1\n    return True\n```\n\nthe severity assigned is low, since, as mentioned, this would be a very unusual pattern in user-code.\n\n### Patches\n\nfix is tracked in https://github.com/vyperlang/vyper/pull/4644\n\n### Workarounds\ndon't have side effects in expressions which construct zero-length bytestrings.\n\n### References\n_Are there any links users can visit to find out more?_",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "vyper"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "0.4.2rc1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/vyperlang/vyper/security/advisories/GHSA-qhr6-mgqr-mchm"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-47285"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/vyperlang/vyper/pull/4644"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/vyperlang/vyper"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L560-L562"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-691" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-05-16T14:10:25Z",
    "nvd_published_at" : "2025-05-15T18:15:38Z"
  }
}