express-4.22.1.tgz: 2 vulnerabilities (highest severity is: 7.5)

[mend-for-github-com]

Vulnerable Library - express-4.22.1.tgz

Path to dependency file: /package.json

Path to vulnerable library: /node_modules/qs/package.json

Vulnerabilities

Vulnerability	Severity	CVSS	Exploit Maturity	EPSS	Dependency	Type	Fixed in (express version)	Remediation Possible**	Reachability
CVE-2026-4867	High	7.5	Not Defined	0.1%	path-to-regexp-0.1.12.tgz	Transitive	N/A*	❌
CVE-2026-2391	Low	3.7	Not Defined	0.1%	qs-6.14.1.tgz	Transitive	5.1.0	✅

*For some transitive vulnerabilities, there is no version of direct dependency with a fix. Check the "Details" section below to see if there is a version of transitive dependency where vulnerability is fixed.

**In some cases, Remediation PR cannot be created automatically for a vulnerability despite the availability of remediation

Details

CVE-2026-4867

Vulnerable Library - path-to-regexp-0.1.12.tgz

Express style path to RegExp utility

Library home page: https://registry.npmjs.org/path-to-regexp/-/path-to-regexp-0.1.12.tgz

Path to dependency file: /package.json

Path to vulnerable library: /node_modules/path-to-regexp/package.json

Dependency Hierarchy:

• express-4.22.1.tgz (Root Library)
  • ❌ path-to-regexp-0.1.12.tgz (Vulnerable Library)

Found in base branch: master

Vulnerability Details

Impact:
A bad regular expression is generated any time you have three or more parameters within a single segment, separated by something that is not a period (.). For example, /:a-:b-:c or /:a-:b-:c-:d. The backtrack protection added in path-to-regexp@0.1.12 only prevents ambiguity for two parameters. With three or more, the generated lookahead does not block single separator characters, so capture groups overlap and cause catastrophic backtracking.
Patches:
Upgrade to path-to-regexp@0.1.13
Custom regex patterns in route definitions (e.g., /:a-:b([^-/]+)-:c([^-/]+)) are not affected because they override the default capture group.
Workarounds:
All versions can be patched by providing a custom regular expression for parameters after the first in a single segment. As long as the custom regular expression does not match the text before the parameter, you will be safe. For example, change /:a-:b-:c to /:a-:b([^-/]+)-:c([^-/]+).
If paths cannot be rewritten and versions cannot be upgraded, another alternative is to limit the URL length.

Publish Date: 2026-03-26

URL: CVE-2026-4867

Threat Assessment

Exploit Maturity: Not Defined

EPSS: 0.1%

CVSS 3 Score Details (7.5)

Base Score Metrics:

• Exploitability Metrics:
  • Attack Vector: Network
  • Attack Complexity: Low
  • Privileges Required: None
  • User Interaction: None
  • Scope: Unchanged
• Impact Metrics:
  • Confidentiality Impact: None
  • Integrity Impact: None
  • Availability Impact: High

For more information on CVSS3 Scores, click here.

Suggested Fix

Type: Upgrade version

Origin: GHSA-37ch-88jc-xwx2

Release Date: 2026-03-26

Fix Resolution: path-to-regexp - 0.1.13

CVE-2026-2391

Vulnerable Library - qs-6.14.1.tgz

A querystring parser that supports nesting and arrays, with a depth limit

Library home page: https://registry.npmjs.org/qs/-/qs-6.14.1.tgz

Path to dependency file: /package.json

Path to vulnerable library: /node_modules/qs/package.json

Dependency Hierarchy:

• express-4.22.1.tgz (Root Library)
  • ❌ qs-6.14.1.tgz (Vulnerable Library)

Found in base branch: master

Vulnerability Details

Summary
The "arrayLimit" option in qs does not enforce limits for comma-separated values when "comma: true" is enabled, allowing attackers to cause denial-of-service via memory exhaustion. This is a bypass of the array limit enforcement, similar to the bracket notation bypass addressed in GHSA-6rw7-vpxm-498p (CVE-2025-15284).
Details
When the "comma" option is set to "true" (not the default, but configurable in applications), qs allows parsing comma-separated strings as arrays (e.g., "?param=a,b,c" becomes "['a', 'b', 'c']"). However, the limit check for "arrayLimit" (default: 20) and the optional throwOnLimitExceeded occur after the comma-handling logic in "parseArrayValue", enabling a bypass. This permits creation of arbitrarily large arrays from a single parameter, leading to excessive memory allocation.
Vulnerable code (lib/parse.js: lines ~40-50):
if (val && typeof val === 'string' && options.comma && val.indexOf(',') > -1) {
    return val.split(',');
}
if (options.throwOnLimitExceeded && currentArrayLength >= options.arrayLimit) {
    throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.');
}
return val;
The "split(',')" returns the array immediately, skipping the subsequent limit check. Downstream merging via "utils.combine" does not prevent allocation, even if it marks overflows for sparse arrays.This discrepancy allows attackers to send a single parameter with millions of commas (e.g., "?param=,,,,,,,,..."), allocating massive arrays in memory without triggering limits. It bypasses the intent of "arrayLimit", which is enforced correctly for indexed ("a[0]=") and bracket ("a[]=") notations (the latter fixed in v6.14.1 per GHSA-6rw7-vpxm-498p).
PoC
Test 1 - Basic bypass:
npm install qs
const qs = require('qs');
const payload = 'a=' + ','.repeat(25); // 26 elements after split (bypasses arrayLimit: 5)
const options = { comma: true, arrayLimit: 5, throwOnLimitExceeded: true };
try {
  const result = qs.parse(payload, options);
  console.log(result.a.length); // Outputs: 26 (bypass successful)
} catch (e) {
  console.log('Limit enforced:', e.message); // Not thrown
}
Configuration:

• "comma: true"
• "arrayLimit: 5"
• "throwOnLimitExceeded: true"
  Expected: Throws "Array limit exceeded" error.
  Actual: Parses successfully, creating an array of length 26.
  Impact
  Denial of Service (DoS) via memory exhaustion.
  Mend Note: The description of this vulnerability differs from MITRE.

Publish Date: 2026-02-12

URL: CVE-2026-2391

Threat Assessment

Exploit Maturity: Not Defined

EPSS: 0.1%

CVSS 3 Score Details (3.7)

Base Score Metrics:

• Exploitability Metrics:
  • Attack Vector: Network
  • Attack Complexity: High
  • Privileges Required: None
  • User Interaction: None
  • Scope: Unchanged
• Impact Metrics:
  • Confidentiality Impact: None
  • Integrity Impact: None
  • Availability Impact: Low

For more information on CVSS3 Scores, click here.

Suggested Fix

Type: Upgrade version

Origin: GHSA-w7fw-mjwx-w883

Release Date: 2026-02-12

Fix Resolution (qs): 6.14.2

Direct dependency fix Resolution (express): 5.1.0

⛑️ Automatic Remediation will be attempted for this issue.

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⛑️Automatic Remediation will be attempted for this issue.