Unsafe ParseInt() Vulnerability: A Critical DoS Attack Vector

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Unsafe parseInt() Vulnerability: A Critical DoS Attack Vector

Hey guys, this article dives deep into a critical security vulnerability related to the use of parseInt() in web applications. We'll explore how improper use of parseInt() without proper validation can expose your applications to Denial of Service (DoS) attacks, potentially leading to service crashes and resource exhaustion. Let's break down the problem, understand the impact, look at real-world attack scenarios, and finally, discuss the necessary fixes and best practices to safeguard your applications. This is important stuff, so pay close attention!

The Problem: parseInt() Calls Without Validation

At the heart of the issue lies the use of parseInt() without proper validation of the input it receives. When developers use parseInt() to convert user-supplied data (like query parameters in a URL) into integers without validating the input, it creates a significant security risk. The primary problem stems from two key areas: the lack of a radix parameter and the absence of NaN (Not a Number) validation. Without these, attackers can manipulate the input to cause resource exhaustion, ultimately leading to a DoS attack.

The Impact: Memory Exhaustion and Service Crashes

The impact of this vulnerability is severe. Attackers can exploit this to cause memory exhaustion on the server. Imagine your application tries to load a massive amount of data into memory because the limit parameter is set to a huge number. This quickly leads to the server running out of resources (like RAM), crashing the service and denying access to legitimate users. The severity here is classified as CRITICAL. It's the kind of thing that can bring your entire system down, and that's never a good day.

Affected Endpoints: Widespread Vulnerability

This vulnerability isn't isolated; it's widespread. The original report identified 12+ affected endpoints across various services. This means multiple parts of your application are potentially vulnerable. It's like having multiple doors unlocked in a building – the more doors open, the easier it is for attackers to get in. Services affected include those related to misinformation, AI safety, and resilience. This broad impact means a comprehensive fix is needed.

Attack Vector: How Attackers Exploit the Vulnerability

So, how does an attacker actually exploit this parseInt() vulnerability? Let's look at some attack scenarios to understand the mechanics:

Scenario 1: The NaN Trick

Attackers can provide non-numeric input. For example, passing ?limit=abc. When parseInt('abc') is called, it returns NaN. Without proper checks, the application might interpret NaN as 0 or use it in other calculations, which leads to unexpected behavior, potentially triggering a full table scan. This can quickly degrade performance and create a DoS situation.

Scenario 2: The Large Number Bomb

Attackers can pass in an extremely large number, such as ?limit=999999999. If the application then tries to allocate that many resources (e.g., loading that many rows from a database), it's likely to cause an OOM (Out Of Memory) crash. The server will simply run out of RAM and the service will go down.

Scenario 3: The Negative Limit Game

Passing a negative value for the limit can also cause problems. For example, using ?limit=-1. Depending on how the application handles the limit, this can lead to unexpected behavior. For example, some database queries might treat a negative limit as an unlimited request, leading to the same memory exhaustion problems.

Vulnerable Code Examples: Real-World Scenarios

To really get a grip on this, let’s look at some real-world examples of vulnerable code. The following code snippet, taken from logs-api/server.js, highlights the problem perfectly:

const limit = parseInt(req.query.limit) || 100;
const logs = db.prepare(`SELECT * FROM log_events LIMIT ?`).all(limit);

Problems with the Code:

  1. Missing Radix Parameter: parseInt() should always have a radix parameter (e.g., parseInt(x, 10)) to specify the base (in this case, base 10 for decimal numbers). Omitting the radix can lead to unexpected behavior, especially with different input formats.
  2. No NaN Handling: The code doesn't check if parseInt() returns NaN. If req.query.limit is something like 'abc', parseInt() will return NaN, but the code doesn't account for it, which defaults to 100 or causes the database to be overwhelmed.
  3. No Maximum Limit Validation: There's no check to limit the maximum value of the limit parameter. This means an attacker can provide a huge number, leading to memory exhaustion.
  4. No Positive Integer Validation: The code doesn't ensure that the result is a positive integer. This can lead to unexpected behavior if negative values or other invalid inputs are provided.

Real-World Impact: The DoS Attack in Action

Let’s see what happens when an attacker exploits this vulnerability in the real world:

# Attacker sends:
curl "http://localhost:5008/api/logs?limit=999999999"

# Server attempts to load 999M rows into memory
# Node.js heap exhausted
# Process crashes
# PM2 restarts
# Attacker repeats → continuous crashes

In this scenario, an attacker sends a malicious request with a huge limit value. The server, without proper validation, tries to load an enormous amount of data into memory, which exhausts the available resources. This causes the Node.js heap to be exhausted, leading to a crash and, potentially, the server restarting. An attacker can repeat this process, causing a continuous cycle of crashes, effectively denying service to legitimate users.

The Required Fix: Implementing Safe Integer Parsing

The most important thing to fix this problem is to create a safe parsing utility. This utility should validate the input, set default values, and enforce maximum and minimum bounds. Here’s how you can do it:

SafeParseInt Function

/**
 * Safely parse integer from user input with bounds checking
 * @param {string|number} value - User input
 * @param {number} defaultValue - Default if invalid
 * @param {number} min - Minimum allowed value
 * @param {number} max - Maximum allowed value
 * @returns {number} Safe integer within bounds
 */
function safeParseInt(value, defaultValue = 100, min = 1, max = 1000) {
  const parsed = parseInt(value, 10);

  if (Number.isNaN(parsed)) {
    return defaultValue;
  }

  return Math.min(Math.max(parsed, min), max);
}

This safeParseInt() function does the following:

  1. Parses the Input: It uses parseInt(value, 10) to parse the input to an integer, using base 10.
  2. Handles NaN: It checks if the parsed value is NaN. If it is, it returns the defaultValue.
  3. Applies Bounds: It uses Math.min() and Math.max() to ensure the parsed value falls within the specified min and max bounds.

Implementing the Fix

To implement the fix, you replace the vulnerable code with the following:

const limit = safeParseInt(req.query.limit, 100, 1, 1000);
const offset = safeParseInt(req.query.offset, 0, 0, 1000000);

By using safeParseInt(), you ensure that the limit and offset values are always within safe bounds, preventing DoS attacks.

Recommended Limits for Parameters

To make sure you're protecting your application, you should also establish recommended limits for certain parameters. Here are a few examples, as mentioned in the original report:

  • limit: Default 100, maximum 1000.
  • offset: Default 0, maximum 1000000.
  • windowHours: Default 24, maximum 720 (30 days).
  • page: Default 1, minimum 1, maximum 10000.

These limits provide a safeguard against excessively large values that could lead to resource exhaustion.

Testing: Validating the Fix

After implementing the fix, testing is crucial. Here are a few test cases you can use:

# Test NaN handling
curl "http://localhost:5008/api/logs?limit=abc"
# Should return 100 results (default), not crash

# Test huge number
curl "http://localhost:5008/api/logs?limit=999999999"
# Should return 1000 results (max), not OOM

# Test negative
curl "http://localhost:5008/api/logs?limit=-1"
# Should return 100 results (default), not error

These tests confirm that the safeParseInt() function correctly handles invalid inputs (like abc), large numbers, and negative values, and will not cause crashes. This testing process should be automated as part of your application's continuous integration and continuous delivery (CI/CD) pipeline.

Related Issues: Other Vulnerable Parameters

It’s important to note that the limit parameter isn’t the only one at risk. Other parameters, such as offset, windowHours (in the nlp-api), and page, can also be exploited in similar ways. Make sure you apply the same validation techniques to these parameters to fully protect your application.

Priority: P0 - Immediate Action Required

This vulnerability is labeled as P0 (Priority 0), meaning it's a critical issue that must be fixed immediately before deploying to production. This is because it represents a trivial DoS attack that can be easily exploited, potentially leading to service disruption and significant downtime. Addressing this vulnerability should be your top priority to ensure the security and stability of your application.

That's it, guys! Remember to always validate user input and set reasonable bounds to prevent this kind of attack. Stay safe out there, and keep those applications secure!