CVE-2020-35917: Pyo3 Reference Counting Error Vulnerability

MODERATE
Advisory Identifier: GHSA-2vx6-fcw6-hpr6
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CVSS 5.5
CWE-416
Published
Advisory Summary

CVE-2020-35917 is a MODERATE (CVSS 5.5) reference counting error vulnerability (CWE-416: Use After Free) affecting Pyo3 libraries in the crates.io ecosystem. The issue involves reference counting error in pyo3. Remediation is available by upgrading affected packages to version 0.12.4.

CVE-2020-35917 at a Glance

CVE Identifier CVE-2020-35917
GHSA Identifier GHSA-2vx6-fcw6-hpr6
Severity MODERATE
CVSS v3.1 Base Score 5.5
CWE Classification CWE-416: Use After Free
Affected Product Pyo3
Package Ecosystem crates.io
Published Date
Last Updated

Security Impact

CVSS: 5.5

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

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

How to Fix CVE-2020-35917

To remediate this vulnerability, upgrade all affected Pyo3 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

pyo3 fixed: 0.12.4 
Upgrade pyo3 to 0.12.4
Verify Direct and Transitive Dependencies

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

inspect dependencies for pyo3

How to Check if You Are Affected

To determine whether your application is affected by CVE-2020-35917, inspect your project dependencies for Pyo3:

inspect dependencies for pyo3

Analyze the terminal output to locate any version of Pyo3 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.12.4), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-416: Use After Free, where the product reuses or references memory after it has been freed. at some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer. In Pyo3, 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

An issue was discovered in the pyo3 crate before 0.12.4 for Rust. There is a reference-counting error and use-after-free in From<Py<T>>.

CVE-2020-35917 Affected Pyo3 Versions

1 component(s)
Fixed Versions:
0.12.4
Product / Package Ecosystem Affected Versions Fixed Version
pyo3
 crates.io
≥ 0.12.0
< 0.12.4
0.12.4

References

NVD — CVE-2020-35917 NVD
https://nvd.nist.gov/vuln/detail/CVE-2020-35917
Pyo3 Source Repository REPOSITORY
https://github.com/PyO3/pyo3/pull/1297
Security Fix Commit FIX COMMIT
https://github.com/PyO3/pyo3/commit/8f81f595dd770b586c7ca7195b42004a6c976eb9
Pyo3 Source Repository REPOSITORY
https://github.com/PyO3/pyo3
rustsec.org/advisories/rustsec-... WEB
https://rustsec.org/advisories/RUSTSEC-2020-0074.html

Frequently Asked Questions

What is CVE-2020-35917?
CVE-2020-35917 is a security vulnerability in Pyo3 involving Reference counting error in pyo3 under CWE-416: Use After Free.
Which Pyo3 versions are affected?
Affected versions include releases prior to 0.12.4 across affected packages: pyo3.
What version fixes CVE-2020-35917?
Upgrading to 0.12.4 (or the latest patched release for your respective branch) resolves the vulnerability.
Is pyo3 affected?
Yes, pyo3 is affected in releases prior to 0.12.4. Upgrade your dependency to 0.12.4 or later.
What is the CVSS score of CVE-2020-35917?
CVE-2020-35917 has a CVSS v3.1 base score of 5.5 (MODERATE) with vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2020-35917?
CVE-2020-35917 is classified under CWE-416: Use After Free (The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.).
How can I check crates.io dependencies for CVE-2020-35917?
Run the dependency tree command: 'inspect dependencies for pyo3'. 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-2vx6-fcw6-hpr6",
  "modified" : "2021-08-19T20:50:20Z",
  "published" : "2021-08-25T20:49:52Z",
  "aliases" : [ "CVE-2020-35917" ],
  "summary" : "Reference counting error in pyo3",
  "details" : "An issue was discovered in the pyo3 crate before 0.12.4 for Rust. There is a reference-counting error and use-after-free in From<Py<T>>.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "pyo3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.12.0"
      }, {
        "fixed" : "0.12.4"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2020-35917"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/PyO3/pyo3/pull/1297"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/PyO3/pyo3/commit/8f81f595dd770b586c7ca7195b42004a6c976eb9"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/PyO3/pyo3"
  }, {
    "type" : "WEB",
    "url" : "https://rustsec.org/advisories/RUSTSEC-2020-0074.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-416" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-08-19T20:50:20Z",
    "nvd_published_at" : null
  }
}