CVE-2025-47774: Vyper Vyper's `slice()` May Elide Side-effects Vulnerability

LOW
Advisory Identifier: GHSA-3vcg-j39x-cwfm
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CWE-691
Published
Advisory Summary

CVE-2025-47774 is a LOW vyper's `slice()` may elide side-effects vulnerability (CWE-691: Insufficient Control Flow Management) affecting Vyper libraries in the PyPI ecosystem. The issue involves vyper's `slice()` may elide side-effects when output length is 0. Remediation is available in the latest vendor maintenance releases.

CVE-2025-47774 at a Glance

CVE Identifier CVE-2025-47774
GHSA Identifier GHSA-3vcg-j39x-cwfm
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-2025-47774

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-2025-47774, 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 the `slice()` builtin can elide side effects when the output length is 0, and the source bytestring is a builtin (`msg.data` or `<address>.code`). the reason is that for these source locations, the check that `length >= 1` is skipped: https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L315-L319 the result is that a 0-length bytestring constructed with slice can be passed to `make_byte_array_copier`, which elides evaluation of its source argument when the max length is 0: https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/codegen/core.py#L189-L191 the impact is that side effects in the `start` argument may be elided when the `length` argument is 0, e.g. `slice(msg.data, self.do_side_effect(), 0)`. the following example illustrates how the issue would look in user code ```vyper counter: public(uint256) @external def test() -> Bytes[10]: b: Bytes[10] = slice(msg.data, self.side_effect(), 0) return b def side_effect() -> uint256: self.counter += 1 return 0 ``` the severity assigned is low, since this is not a very useful pattern and unlikely to be found in user code. ### Patches the fix is tracked in https://github.com/vyperlang/vyper/pull/4645, which disallows any invocation of `slice()` with length 0, including for the ad hoc locations discussed in this advisory. ### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_ ### References _Are there any links users can visit to find out more?_

CVE-2025-47774 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-3vcg-j39x-cwfm
NVD — CVE-2025-47774 NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-47774
Vyper Source Repository REPOSITORY
https://github.com/vyperlang/vyper/pull/4645
Vyper Source Repository REPOSITORY
https://github.com/vyperlang/vyper
Vyper Source Repository REPOSITORY
https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L315-L319
Vyper Source Repository REPOSITORY
https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/codegen/core.py#L189-L191

Frequently Asked Questions

What is CVE-2025-47774?
CVE-2025-47774 is a security vulnerability in Vyper involving Vyper's `slice()` may elide side-effects when output length is 0 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-2025-47774?
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-2025-47774?
CVE-2025-47774 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-2025-47774?
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-3vcg-j39x-cwfm",
  "modified" : "2025-05-16T14:13:29Z",
  "published" : "2025-05-16T14:13:29Z",
  "aliases" : [ "CVE-2025-47774" ],
  "summary" : "Vyper's `slice()` may elide side-effects when output length is 0",
  "details" : "### Impact\nthe `slice()` builtin can elide side effects when the output length is 0, and the source bytestring is a builtin (`msg.data` or `<address>.code`). the reason is that for these source locations, the check that `length >= 1` is skipped:\nhttps://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L315-L319\n\nthe result is that a 0-length bytestring constructed with slice can be passed to `make_byte_array_copier`, which elides evaluation of its source argument when the max length is 0:\nhttps://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/codegen/core.py#L189-L191\n\nthe impact is that side effects in the `start` argument may be elided when the `length` argument is 0, e.g. `slice(msg.data, self.do_side_effect(), 0)`.\n\nthe following example illustrates how the issue would look in user code\n```vyper\ncounter: public(uint256)\n\n@external\ndef test() -> Bytes[10]:\n    b: Bytes[10] = slice(msg.data, self.side_effect(), 0)\n    return b\n\ndef side_effect() -> uint256:\n    self.counter += 1\n    return 0\n```\n\nthe severity assigned is low, since this is not a very useful pattern and unlikely to be found in user code.\n\n### Patches\n\nthe fix is tracked in https://github.com/vyperlang/vyper/pull/4645, which disallows any invocation of `slice()` with length 0, including for the ad hoc locations discussed in this advisory.\n\n### Workarounds\n_Is there a way for users to fix or remediate the vulnerability without upgrading?_\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-3vcg-j39x-cwfm"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-47774"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/vyperlang/vyper/pull/4645"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/vyperlang/vyper"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L315-L319"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/codegen/core.py#L189-L191"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-691" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-05-16T14:13:29Z",
    "nvd_published_at" : "2025-05-15T18:15:38Z"
  }
}