CVE-2024-21503: Black Denial of Service Vulnerability

MODERATE
Advisory Identifier: GHSA-fj7x-q9j7-g6q6
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CVSS 5.3
CWE-1333 CWE-75
Published
Advisory Summary

CVE-2024-21503 is a MODERATE (CVSS 5.3) denial of service vulnerability (CWE-1333: Inefficient Regular Expression Complexity) affecting Black libraries in the PyPI ecosystem. The issue involves black vulnerable to regular expression denial of service (redos). Remediation is available by upgrading affected packages to version 24.3.0.

CVE-2024-21503 at a Glance

CVE Identifier CVE-2024-21503
GHSA Identifier GHSA-fj7x-q9j7-g6q6
Severity MODERATE
CVSS v3.1 Base Score 5.3
CWE Classification CWE-1333: Inefficient Regular Expression Complexity
Affected Product Black
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:N/A:L).

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 None (I:N)
Availability Low (A:L)

How to Fix CVE-2024-21503

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

black fixed: 24.3.0 
pip install black>=24.3.0
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 black

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2024-21503, inspect your installed packages using pip:

pip show black

Analyze the terminal output to locate any version of Black in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 24.3.0), your application is affected.

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

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-1333: Inefficient Regular Expression Complexity, where the product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential. In Black, 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

Versions of the package black before 24.3.0 are vulnerable to Regular Expression Denial of Service (ReDoS) via the lines_with_leading_tabs_expanded function in the strings.py file. An attacker could exploit this vulnerability by crafting a malicious input that causes a denial of service. Exploiting this vulnerability is possible when running Black on untrusted input, or if you habitually put thousands of leading tab characters in your docstrings.

CVE-2024-21503 Affected Black Versions

1 component(s)
Fixed Versions:
24.3.0
Product / Package Ecosystem Affected Versions Fixed Version
black
pypi/black
PyPI
< 24.3.0
24.3.0

References

NVD — CVE-2024-21503 NVD
https://nvd.nist.gov/vuln/detail/CVE-2024-21503
Security Fix Commit FIX COMMIT
https://github.com/psf/black/commit/f00093672628d212b8965a8993cee8bedf5fe9b8
Black Source Repository REPOSITORY
https://github.com/psf/black
Black Release RELEASE
https://github.com/psf/black/releases/tag/24.3.0
Black Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/black/PYSEC-2024-48.yaml
Black Security Information SECURITY
https://security.snyk.io/vuln/SNYK-PYTHON-BLACK-6256273

Frequently Asked Questions

What is CVE-2024-21503?
CVE-2024-21503 is a security vulnerability in Black involving Black vulnerable to Regular Expression Denial of Service (ReDoS) under CWE-1333: Inefficient Regular Expression Complexity.
Which Black versions are affected?
Affected versions include releases prior to 24.3.0 across affected packages: black.
What version fixes CVE-2024-21503?
Upgrading to 24.3.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is black affected?
Yes, black is affected in releases prior to 24.3.0. Upgrade your dependency to 24.3.0 or later.
What is the CVSS score of CVE-2024-21503?
CVE-2024-21503 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:N/A:L.
What CWE is associated with CVE-2024-21503?
CVE-2024-21503 is classified under CWE-1333: Inefficient Regular Expression Complexity (The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.).
How can I check PyPI dependencies for CVE-2024-21503?
Run the dependency tree command: 'pip show black'. 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-fj7x-q9j7-g6q6",
  "modified" : "2024-03-20T15:24:01Z",
  "published" : "2024-03-19T06:30:52Z",
  "aliases" : [ "CVE-2024-21503" ],
  "summary" : "Black vulnerable to Regular Expression Denial of Service (ReDoS)",
  "details" : "Versions of the package black before 24.3.0 are vulnerable to Regular Expression Denial of Service (ReDoS) via the lines_with_leading_tabs_expanded function in the strings.py file. An attacker could exploit this vulnerability by crafting a malicious input that causes a denial of service.\n\nExploiting this vulnerability is possible when running Black on untrusted input, or if you habitually put thousands of leading tab characters in your docstrings.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "black"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "24.3.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2024-21503"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/psf/black/commit/f00093672628d212b8965a8993cee8bedf5fe9b8"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/psf/black"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/psf/black/releases/tag/24.3.0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/black/PYSEC-2024-48.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://security.snyk.io/vuln/SNYK-PYTHON-BLACK-6256273"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1333", "CWE-75" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2024-03-20T15:24:01Z",
    "nvd_published_at" : "2024-03-19T05:15:09Z"
  }
}