CVE-2026-110816 (Medium) detected in qs-6.15.1.tgz

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
javascript, node.js
Domain
frontend, security

Research direction

The vulnerable qs 6.15.1 is pulled in transitively under the /ui project (via cypress and request), so start with ui/package.json and the pnpm lockfile to see how qs is resolved. The advisory says the fix ships in qs 6.16.1, so the change is a resolution bump, possibly with a pnpm override. Done when the lockfile resolves qs to 6.16.1 or later and the UI install and build still pass.

Written by the indexing model from the issue text.

Description

Mend: dependency security vulnerability

CVE-2026-110816 - Medium Severity Vulnerability

Vulnerable Library - qs-6.15.1.tgz

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

Library home page: https://registry.npmjs.org/qs/-/qs-6.15.1.tgz

Sample Path to Dependency File: /ui/package.json

Path to vulnerable library: /ui/node_modules/.pnpm/[email protected]/node_modules/qs/package.json

Dependency Hierarchy:

  • @⁠postgres.ai/ce-4.0.3.tgz (Root Library)
    • cypress-14.5.4.tgz
      • request-3.0.10.tgz
        • ❌ qs-6.15.1.tgz (Vulnerable Library)

Found in base branch: master

Vulnerability Details

Summary
"qs.stringify" with "arrayFormat: 'comma'" throws "TypeError: Cannot convert object to primitive value" when an array element cannot be coerced to a string, such as an object with an own non-callable "toString" ("{ "toString": "x" }") or a null-prototype object. The comma format joins array elements with "Array.prototype.join" and, under "encodeValuesOnly", first passes each element through "String()" in "utils.encode"; neither guards against an element whose string coercion fails.
Details
In "lib/stringify.js", the comma branch collapses the array with "obj.join(',')". For an element whose own "toString" is not callable, "ToPrimitive" skips it, falls through to "Object.prototype.valueOf" (which returns the object itself), and throws. Under "encodeValuesOnly: true", the same element first reaches "String(str)" in "utils.encode" ("lib/utils.js") and throws there. Nested arrays ("{ "a": [[{ "toString": "x" }]] }") throw the same way, through "Array.prototype.toString". The "indices", "brackets", and "repeat" formats walk into object elements instead of coercing them, and are not affected.
Such elements can come from untrusted input. "JSON.parse" produces "{ "a": [{ "toString": "x" }] }" with no qs option involved. "qs.parse("a[0][toString]=x", { allowPrototypes: true })" keeps the "toString" key, and "qs.parse("a[][b]=c", { plainObjects: true })" produces a null-prototype element; the default parse options drop "toString" and produce ordinary objects, which do not throw. Express 4's default "query parser", Express 5's "extended" query parser, and body-parser's "urlencoded({ extended: true })" all call "qs.parse" with "allowPrototypes: true".
PoC
Fix
Applied in a952e75 on "main" and released as v6.16.1: an element whose string coercion would fail is coerced to its primitive "valueOf", if any, or else to "Object.prototype.toString", so it renders as "[object Object]", the same as any other object element already does under the comma format. Nested arrays are walked the way "join" walks them. Every input that did not previously throw serializes exactly as before, and a "toString" or "valueOf" that itself throws still propagates.
Affected versions
">=6.7.0 <6.16.1", fixed in v6.16.1.
The "join" path was introduced with the comma format in b84acba and first shipped in v6.7.0; v6.6.x and earlier ignore "arrayFormat: 'comma'" and are not affected. The "encodeValuesOnly" "String()" site was introduced in 4c4b23d (v6.11.1); before that, the same input throws at "join". Every release from v6.7.0 through v6.16.0 is affected.
Impact
An unauthenticated request can make any code path that re-serializes attacker-influenced data with "qs.stringify" and "arrayFormat: 'comma'" (for example, rebuilding a query string from "req.query" for a redirect or an upstream request, or serializing a parsed JSON body) throw synchronously. In a typical Node.js HTTP framework the throw is caught by the framework error boundary and the affected request returns a 500; the process survives and other requests are unaffected. Where the call runs outside an error boundary, such as an "async" Express 4 handler (where the throw becomes an unhandled promise rejection) or a bare "http" request handler, the process exits, so the impact in that case depends on the application error handling rather than on qs. The default "arrayFormat" ("indices") is not affected.
Mend Note: The description of this vulnerability differs from MITRE.

Publish Date: 2026-10-14

URL: CVE-2026-110816

CVSS 3 Score Details (5.3)

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: Low

For more information on CVSS3 Scores, click here.

Suggested Fix

Type: Upgrade version

Origin: https://github.com/advisories/GHSA-6pq8-jhm2-2vcw

Release Date: 2026-10-14

Fix Resolution: qs - 6.16.1

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