Version Details and Security Vulnerabilities

The request package through 2.88.2 for Node.js and the @cypress/request package prior to 3.0.0 allow a bypass of SSRF mitigations via an attacker-controller server that does a cross-protocol redirect (HTTP to HTTPS, or HTTPS to HTTP).

NOTE: The request package is no longer supported by the maintainer.

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).

Summary

form-data uses Math.random() to select a boundary value for multipart form-encoded data. This can lead to a security issue if an attacker:

1. can observe other values produced by Math.random in the target application, and
2. can control one field of a request made using form-data

Because the values of Math.random() are pseudo-random and predictable (see: https://blog.securityevaluators.com/hacking-the-javascript-lottery-80cc437e3b7f), an attacker who can observe a few sequential values can determine the state of the PRNG and predict future values, includes those used to generate form-data's boundary value. The allows the attacker to craft a value that contains a boundary value, allowing them to inject additional parameters into the request.

This is largely the same vulnerability as was recently found in undici by parrot409 -- I'm not affiliated with that researcher but want to give credit where credit is due! My PoC is largely based on their work.

Details

The culprit is this line here: https://github.com/form-data/form-data/blob/426ba9ac440f95d1998dac9a5cd8d738043b048f/lib/form_data.js#L347

An attacker who is able to predict the output of Math.random() can predict this boundary value, and craft a payload that contains the boundary value, followed by another, fully attacker-controlled field. This is roughly equivalent to any sort of improper escaping vulnerability, with the caveat that the attacker must find a way to observe other Math.random() values generated by the application to solve for the state of the PRNG. However, Math.random() is used in all sorts of places that might be visible to an attacker (including by form-data itself, if the attacker can arrange for the vulnerable application to make a request to an attacker-controlled server using form-data, such as a user-controlled webhook -- the attacker could observe the boundary values from those requests to observe the Math.random() outputs). A common example would be a x-request-id header added by the server. These sorts of headers are often used for distributed tracing, to correlate errors across the frontend and backend. Math.random() is a fine place to get these sorts of IDs (in fact, opentelemetry uses Math.random for this purpose)

PoC

PoC here: https://github.com/benweissmann/CVE-2025-7783-poc

Instructions are in that repo. It's based on the PoC from https://hackerone.com/reports/2913312 but simplified somewhat; the vulnerable application has a more direct side-channel from which to observe Math.random() values (a separate endpoint that happens to include a randomly-generated request ID).

Impact

For an application to be vulnerable, it must:

• Use form-data to send data including user-controlled data to some other system. The attacker must be able to do something malicious by adding extra parameters (that were not intended to be user-controlled) to this request. Depending on the target system's handling of repeated parameters, the attacker might be able to overwrite values in addition to appending values (some multipart form handlers deal with repeats by overwriting values instead of representing them as an array)
• Reveal values of Math.random(). It's easiest if the attacker can observe multiple sequential values, but more complex math could recover the PRNG state to some degree of confidence with non-sequential values.

If an application is vulnerable, this allows an attacker to make arbitrary requests to internal systems.

Versions of the package tough-cookie before 4.1.3 are vulnerable to Prototype Pollution due to improper handling of Cookies when using CookieJar in rejectPublicSuffixes=false mode. This issue arises from the manner in which the objects are initialized.