CVE-2021-38305: Yamale Command Injection Vulnerability

HIGH
Advisory Identifier: GHSA-435p-f82x-mxwm
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CVSS 7.8
CWE-78 CWE-434
Published
Advisory Summary

CVE-2021-38305 is a HIGH (CVSS 7.8) command injection vulnerability (CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')) affecting Yamale libraries in the PyPI ecosystem. The issue involves command injection in yamale. Remediation is available by upgrading affected packages to version 3.0.8.

CVE-2021-38305 at a Glance

CVE Identifier CVE-2021-38305
GHSA Identifier GHSA-435p-f82x-mxwm
Severity HIGH
CVSS v3.1 Base Score 7.8
CWE Classification CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
Affected Product Yamale
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 7.8

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

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

How to Fix CVE-2021-38305

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

yamale fixed: 3.0.8 
pip install yamale>=3.0.8
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 yamale

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2021-38305, inspect your installed packages using pip:

pip show yamale

Analyze the terminal output to locate any version of Yamale in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.0.8), your application is affected.

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

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection'), where the product constructs all or part of an os command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended os command when it is sent to a downstream component. In Yamale, 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

23andMe Yamale before 3.0.8 allows remote attackers to execute arbitrary code via a crafted schema file. The schema parser uses eval as part of its processing, and tries to protect from malicious expressions by limiting the builtins that are passed to the eval. When processing the schema, each line is run through Python's eval function to make the validator available. A well-constructed string within the schema rules can execute system commands; thus, by exploiting the vulnerability, an attacker can run arbitrary code on the image that invokes Yamale.

CVE-2021-38305 Affected Yamale Versions

1 component(s)
Fixed Versions:
3.0.8
Product / Package Ecosystem Affected Versions Fixed Version
yamale
pypi/yamale
PyPI
< 3.0.8
3.0.8

References

NVD — CVE-2021-38305 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-38305
Yamale Source Repository REPOSITORY
https://github.com/23andMe/Yamale/pull/165
Yamale Source Repository REPOSITORY
https://github.com/23andMe/Yamale
Yamale Release RELEASE
https://github.com/23andMe/Yamale/releases/tag/3.0.8
Yamale Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/yamale/PYSEC-2021-119.yaml

Frequently Asked Questions

What is CVE-2021-38305?
CVE-2021-38305 is a security vulnerability in Yamale involving Command injection in Yamale under CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection').
Which Yamale versions are affected?
Affected versions include releases prior to 3.0.8 across affected packages: yamale.
What version fixes CVE-2021-38305?
Upgrading to 3.0.8 (or the latest patched release for your respective branch) resolves the vulnerability.
Is yamale affected?
Yes, yamale is affected in releases prior to 3.0.8. Upgrade your dependency to 3.0.8 or later.
What is the CVSS score of CVE-2021-38305?
CVE-2021-38305 has a CVSS v3.1 base score of 7.8 (HIGH) with vector string CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2021-38305?
CVE-2021-38305 is classified under CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') (The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.).
How can I check PyPI dependencies for CVE-2021-38305?
Run the dependency tree command: 'pip show yamale'. 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-435p-f82x-mxwm",
  "modified" : "2024-11-19T18:25:44Z",
  "published" : "2021-08-11T15:19:23Z",
  "aliases" : [ "CVE-2021-38305" ],
  "summary" : "Command injection in Yamale",
  "details" : "23andMe Yamale before 3.0.8 allows remote attackers to execute arbitrary code via a crafted schema file. The schema parser uses eval as part of its processing, and tries to protect from malicious expressions by limiting the builtins that are passed to the eval. When processing the schema, each line is run through Python's eval function to make the validator available. A well-constructed string within the schema rules can execute system commands; thus, by exploiting the vulnerability, an attacker can run arbitrary code on the image that invokes Yamale.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "yamale"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.0.8"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-38305"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/23andMe/Yamale/pull/165"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/23andMe/Yamale"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/23andMe/Yamale/releases/tag/3.0.8"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/yamale/PYSEC-2021-119.yaml"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-434", "CWE-78" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-08-10T17:33:14Z",
    "nvd_published_at" : "2021-08-09T21:15:00Z"
  }
}