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Remove direct qs dependency #6865

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Remove direct qs dependency #6865

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7 changes: 7 additions & 0 deletions History.md
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Original file line number Diff line number Diff line change
@@ -1,3 +1,10 @@
unreleased
==========

* Remove `app.set('query parser', 'extended')` option; users should pass a custom parser function instead
- To replicate old `'extended'` behavior: `app.set('query parser', str => require('qs').parse(str, { allowPrototypes: true }))`
- This allows removing `qs` from the dependencies for users who don't configure it explicitly

5.1.0 / 2025-03-31
========================

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20 changes: 2 additions & 18 deletions lib/utils.js
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Expand Up @@ -17,7 +17,6 @@ var contentType = require('content-type');
var etag = require('etag');
var mime = require('mime-types')
var proxyaddr = require('proxy-addr');
var qs = require('qs');
var querystring = require('node:querystring');
const { Buffer } = require('node:buffer');

Expand Down Expand Up @@ -154,7 +153,7 @@ exports.compileETag = function(val) {
/**
* Compile "query parser" value to function.
*
* @param {String|Function} val
* @param {String|Function|Boolean} val
* @return {Function}
* @api private
*/
Expand All @@ -174,8 +173,7 @@ exports.compileQueryParser = function compileQueryParser(val) {
case false:
break;
case 'extended':
fn = parseExtendedQueryString;
break;
throw new TypeError("query parser 'extended' is no longer supported; use: `app.set('query parser', str => qs.parse(str, { allowPrototypes: true }))` to replicate the old behavior");
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Copilot AI Oct 29, 2025

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The error message suggests using { allowPrototypes: true } but this option is a security risk. The old parseExtendedQueryString function used this option, but users migrating should be warned about the security implications or given a safer default option.

Suggested change
throw new TypeError("query parser 'extended' is no longer supported; use: `app.set('query parser', str => qs.parse(str, { allowPrototypes: true }))` to replicate the old behavior");
throw new TypeError("query parser 'extended' is no longer supported. To replicate the old behavior, you may use: `app.set('query parser', str => qs.parse(str, { allowPrototypes: true }))`, but WARNING: enabling `{ allowPrototypes: true }` is a security risk and can lead to prototype pollution vulnerabilities. Do not use this option in production unless you fully understand the risks. The default behavior is safer and recommended.");

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@lukaselmer lukaselmer Oct 29, 2025

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ljharb/qs#321 => allowPrototypes: true is not a security issue

default:
throw new TypeError('unknown value for query parser function: ' + val);
}
Expand Down Expand Up @@ -255,17 +253,3 @@ function createETagGenerator (options) {
return etag(buf, options)
}
}

/**
* Parse an extended query string with qs.
*
* @param {String} str
* @return {Object}
* @private
*/

function parseExtendedQueryString(str) {
return qs.parse(str, {
allowPrototypes: true
});
}
2 changes: 1 addition & 1 deletion package.json
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Expand Up @@ -52,7 +52,6 @@
"once": "^1.4.0",
"parseurl": "^1.3.3",
"proxy-addr": "^2.0.7",
"qs": "^6.14.0",
"range-parser": "^1.2.1",
"router": "^2.2.0",
"send": "^1.1.0",
Expand All @@ -76,6 +75,7 @@
"morgan": "1.10.1",
"nyc": "^17.1.0",
"pbkdf2-password": "1.2.1",
"qs": "^6.14.0",
"supertest": "^6.3.0",
"vhost": "~3.0.2"
},
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15 changes: 12 additions & 3 deletions test/req.query.js
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
'use strict'

var assert = require('node:assert')
var qs = require('qs');
var express = require('../')
, request = require('supertest');

Expand All @@ -22,24 +23,32 @@ describe('req', function(){
.expect(200, '{"user[name]":"tj"}', done);
});

describe('when "query parser" is extended', function () {
describe('when "query parser" is set to qs (formerly "extended")', function () {
it('should parse complex keys', function (done) {
var app = createApp('extended');
var app = createApp(qs.parse);

request(app)
.get('/?foo[0][bar]=baz&foo[0][fizz]=buzz&foo[]=done!')
.expect(200, '{"foo":[{"bar":"baz","fizz":"buzz"},"done!"]}', done);
});

it('should parse parameters with dots', function (done) {
var app = createApp('extended');
var app = createApp(qs.parse);

request(app)
.get('/?user.name=tj')
.expect(200, '{"user.name":"tj"}', done);
});
});

describe('when "query parser" is set to extended', function () {
it('should throw with a helpful error message', function () {
assert.throws(() => createApp('extended'),
new TypeError("query parser 'extended' is no longer supported; use: `app.set('query parser', str => qs.parse(str, { allowPrototypes: true }))` to replicate the old behavior")
);
});
});

describe('when "query parser" is simple', function () {
it('should not parse complex keys', function (done) {
var app = createApp('simple');
Expand Down