CVE-2021-38196: Better macro Remote Code Execution Vulnerability

HIGH
Advisory Identifier: GHSA-79wf-qcqv-r22r
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CVSS 9.8
CWE-78 CWE-94
Published
Advisory Summary

CVE-2021-38196 is a HIGH (CVSS 9.8) remote code execution vulnerability (CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')) affecting Better macro libraries in the crates.io ecosystem. The issue involves remote code execution in better-macro. Remediation is available in the latest vendor maintenance releases.

CVE-2021-38196 at a Glance

CVE Identifier CVE-2021-38196
GHSA Identifier GHSA-79wf-qcqv-r22r
Severity HIGH
CVSS v3.1 Base Score 9.8
CWE Classification CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
Affected Product Better macro
Package Ecosystem crates.io
Published Date
Last Updated

Security Impact

CVSS: 9.8

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:H/I:H/A:H).

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 High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2021-38196

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

better-macro fixed: Latest secure release 
Upgrade better-macro to 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: 

inspect dependencies for better-macro

How to Check if You Are Affected

To determine whether your application is affected by CVE-2021-38196, inspect your project dependencies for Better macro:

inspect dependencies for better-macro

Analyze the terminal output to locate any version of Better macro 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: Verify declared build manifests and deployed runtime container environments.

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 Better macro, 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 better-macro crate through 2021-07-22 for Rust. It intentionally demonstrates that remote attackers can execute arbitrary code via proc-macros, and otherwise has no legitimate purpose.

CVE-2021-38196 Affected Better macro Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
better-macro
 crates.io
≤ 1.0.4

References

NVD — CVE-2021-38196 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-38196
Better macro Source Repository REPOSITORY
https://github.com/raycar5/better-macro
Better macro Source Repository REPOSITORY
https://github.com/raycar5/better-macro/blob/24ff1702397b9c19bbfa4c660e2316cd77d3b900/src/lib.rs#L36-L38
rustsec.org/advisories/rustsec-... WEB
https://rustsec.org/advisories/RUSTSEC-2021-0077.html

Frequently Asked Questions

What is CVE-2021-38196?
CVE-2021-38196 is a security vulnerability in Better macro involving Remote code execution in better-macro under CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection').
Which Better macro versions are affected?
Affected versions include releases prior to current release patches across affected packages: better-macro.
What version fixes CVE-2021-38196?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is better-macro affected?
Yes, better-macro is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
What is the CVSS score of CVE-2021-38196?
CVE-2021-38196 has a CVSS v3.1 base score of 9.8 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2021-38196?
CVE-2021-38196 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 crates.io dependencies for CVE-2021-38196?
Run the dependency tree command: 'inspect dependencies for better-macro'. 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-79wf-qcqv-r22r",
  "modified" : "2021-08-18T21:21:03Z",
  "published" : "2021-08-25T20:56:00Z",
  "aliases" : [ "CVE-2021-38196" ],
  "summary" : "Remote code execution in better-macro",
  "details" : "An issue was discovered in the better-macro crate through 2021-07-22 for Rust. It intentionally demonstrates that remote attackers can execute arbitrary code via proc-macros, and otherwise has no legitimate purpose.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "better-macro"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "1.0.4"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-38196"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/raycar5/better-macro"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/raycar5/better-macro/blob/24ff1702397b9c19bbfa4c660e2316cd77d3b900/src/lib.rs#L36-L38"
  }, {
    "type" : "WEB",
    "url" : "https://rustsec.org/advisories/RUSTSEC-2021-0077.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-78", "CWE-94" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-08-18T21:21:03Z",
    "nvd_published_at" : "2021-08-08T06:15:00Z"
  }
}