CVE-2024-32646: Vyper Vyper Performs Double Eval Of Vulnerability

MODERATE
Advisory Identifier: GHSA-r56x-j438-vw5m
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CVSS 5.3
CWE-20
Published
Advisory Summary

CVE-2024-32646 is a MODERATE (CVSS 5.3) vyper performs double eval of vulnerability (CWE-20: Improper Input Validation) affecting Vyper libraries in the PyPI ecosystem. The issue involves vyper performs double eval of the slice start/length args in certain cases. Remediation is available by upgrading affected packages to version 0.4.0.

CVE-2024-32646 at a Glance

CVE Identifier CVE-2024-32646
GHSA Identifier GHSA-r56x-j438-vw5m
Severity MODERATE
CVSS v3.1 Base Score 5.3
CWE Classification CWE-20: Improper Input Validation
Affected Product Vyper
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 5.3

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2024-32646

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: 0.4.0 
pip install vyper>=0.4.0
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-2024-32646, 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 0.4.0), 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-20: Improper Input Validation, where the product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. 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

### Summary Using the `slice` builtin can result in a double eval vulnerability when the buffer argument is either `msg.data`, `self.code` or `<address>.code` and either the `start` or `length` arguments have side-effects. A contract search was performed and no vulnerable contracts were found in production. Having side-effects in the start and length patterns is also an unusual pattern which is not that likely to show up in user code. It is also much harder (but not impossible!) to trigger the bug since `0.3.4` since the unique symbol fence was introduced (https://github.com/vyperlang/vyper/pull/2914). ### Details It can be seen that the `_build_adhoc_slice_node` function of the `slice` builtin doesn't cache the mentioned arguments to the stack: https://github.com/vyperlang/vyper/blob/4595938734d9988f8e46e8df38049ae0559abedb/vyper/builtins/functions.py#L244 As such, they can be evaluated multiple times (instead of retrieving the value from the stack). ### PoC with Vyper version `0.3.3+commit.48e326f` the call to `foo` passes the `asserts`: ```vyper l: DynArray[uint256, 10] @external def foo(cs: String[64]) -> uint256: for i in range(10): self.l.append(1) assert len(self.l) == 10 s: Bytes[64] = b"" s = slice(msg.data, self.l.pop(), 3) assert len(self.l) == 10 - 2 return len(self.l) ``` ### Patches Patched in https://github.com/vyperlang/vyper/pull/3976. ### Impact No vulnerable production contracts were found.

CVE-2024-32646 Affected Vyper Versions

1 component(s)
Fixed Versions:
0.4.0
Product / Package Ecosystem Affected Versions Fixed Version
vyper
pypi/vyper
PyPI
< 0.4.0
0.4.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/vyperlang/vyper/security/advisories/GHSA-r56x-j438-vw5m
NVD — CVE-2024-32646 NVD
https://nvd.nist.gov/vuln/detail/CVE-2024-32646
Vyper Source Repository REPOSITORY
https://github.com/vyperlang/vyper/pull/2914
Vyper Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/vyper/PYSEC-2024-207.yaml
Vyper Source Repository REPOSITORY
https://github.com/vyperlang/vyper

Frequently Asked Questions

What is CVE-2024-32646?
CVE-2024-32646 is a security vulnerability in Vyper involving vyper performs double eval of the slice start/length args in certain cases under CWE-20: Improper Input Validation.
Which Vyper versions are affected?
Affected versions include releases prior to 0.4.0 across affected packages: vyper.
What version fixes CVE-2024-32646?
Upgrading to 0.4.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is vyper affected?
Yes, vyper is affected in releases prior to 0.4.0. Upgrade your dependency to 0.4.0 or later.
What is the CVSS score of CVE-2024-32646?
CVE-2024-32646 has a CVSS v3.1 base score of 5.3 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.
What CWE is associated with CVE-2024-32646?
CVE-2024-32646 is classified under CWE-20: Improper Input Validation (The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.).
How can I check PyPI dependencies for CVE-2024-32646?
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-r56x-j438-vw5m",
  "modified" : "2025-01-21T17:53:57Z",
  "published" : "2024-04-25T19:51:41Z",
  "aliases" : [ "CVE-2024-32646" ],
  "summary" : "vyper performs double eval of the slice start/length args in certain cases",
  "details" : "### Summary\nUsing the `slice` builtin can result in a double eval vulnerability when the buffer argument is either `msg.data`, `self.code` or `<address>.code` and either the `start` or `length` arguments have side-effects.\n\nA contract search was performed and no vulnerable contracts were found in production. Having side-effects in the start and length patterns is also an unusual pattern which is not that likely to show up in user code. It is also much harder (but not impossible!) to trigger the bug since `0.3.4` since the unique symbol fence was introduced (https://github.com/vyperlang/vyper/pull/2914).\n\n### Details\nIt can be seen that the `_build_adhoc_slice_node` function of the `slice` builtin doesn't cache the mentioned arguments to the stack: https://github.com/vyperlang/vyper/blob/4595938734d9988f8e46e8df38049ae0559abedb/vyper/builtins/functions.py#L244\n\nAs such, they can be evaluated multiple times (instead of retrieving the value from the stack).\n\n### PoC\nwith Vyper version `0.3.3+commit.48e326f` the call to `foo` passes the `asserts`:\n```vyper\nl: DynArray[uint256, 10]\n\n@external\ndef foo(cs: String[64]) -> uint256:\n    for i in range(10):\n        self.l.append(1)\n    assert len(self.l) == 10\n    s: Bytes[64] = b\"\"\n    s = slice(msg.data, self.l.pop(), 3)\n    assert len(self.l) == 10 - 2\n    return len(self.l)\n```\n\n### Patches\nPatched in https://github.com/vyperlang/vyper/pull/3976.\n\n### Impact\nNo vulnerable production contracts were found.\n",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "vyper"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.4.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/vyperlang/vyper/security/advisories/GHSA-r56x-j438-vw5m"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2024-32646"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/vyperlang/vyper/pull/2914"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/vyper/PYSEC-2024-207.yaml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/vyperlang/vyper"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2024-04-25T19:51:41Z",
    "nvd_published_at" : "2024-04-25T18:15:08Z"
  }
}