### 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 ```js var qs = require("qs"); qs.stringify(JSON.parse("{\"a\":[{\"toString\":\"x\"}]}"), { arrayFormat: "comma" }); qs.stringify(qs.parse("a[0][toString]=x", { allowPrototypes: true }), { arrayFormat: "comma" }); qs.stringify(qs.parse("a[][b]=c", { plainObjects: true }), { arrayFormat: "comma", encodeValuesOnly: true }); // TypeError: Cannot convert object to primitive value ``` #### 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.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - ### 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 ```js var qs = require("qs");
    qs.stringify(JSON.parse("{\"a\":[{\"toString\":\"x\"}]}"), { arrayFormat: "comma" });
    qs.stringify(qs.parse("a[0][toString]=x", { allowPrototypes: true }), { arrayFormat: "comma" });
    qs.stringify(qs.parse("a[][b]=c", { plainObjects: true }), { arrayFormat: "comma", encodeValuesOnly: true
    }); // TypeError: Cannot convert object to primitive value ``` #### 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. (CVE-2026-110816)

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - ### 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 ```js var qs = require(qs);
    qs.stringify(JSON.parse({\a\:[{\toString\:\x\}]}), { arrayFormat: comma });
    qs.stringify(qs.parse(a[0][toString]=x, { allowPrototypes: true }), { arrayFormat: comma });
    qs.stringify(qs.parse(a[][b]=c, { plainObjects: true }), { arrayFormat: comma, encodeValuesOnly: true     }); // TypeError: Cannot convert object to primitive value ``` #### 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. (CVE-2026-110816)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
477592	SCA: security update for qs (GHSA-6pq8-jhm2-2vcw)	Tenable Cloud Security	SCA Checks	Local	medium
477592	SCA: security update for qs (GHSA-6pq8-jhm2-2vcw)	Tenable Self-Hosted Container Security	SCA Checks	Local	medium
366413	Linux Distros Unpatched Vulnerability : CVE-2026-110816	Nessus	Misc.	Local	medium

Detections

Analytics

CVE-2026-110816

medium

Tenable Plugins

medium

medium

medium