CVE-2023-43848

Executive Summary

CVE-2023-43847 describes an incorrect access control vulnerability in the firewall management function of the web interface for Aten PE6208 power distribution units (PDUs) running firmware versions 2.3.228 and 2.4.232. This flaw allows a remote authenticated user with low privileges to alter local firewall settings as if they were the administrator. The vulnerability is triggered via an HTTP POST request to the firewall management endpoint, bypassing role-based access controls. No patch has been released by the vendor, and no public exploit code is available. The EPSS score is 0.0%, indicating low exploitation likelihood in the wild, but the risk remains for targeted attacks against critical infrastructure.

Supply Chain & Package Security

This vulnerability is not related to any software package ecosystem (NPM, PyPI, Go, Ruby). It affects embedded firmware on a hardware device (Aten PE6208 PDU). No supply chain implications are present.

CVSS Breakdown & Threat Level

The CVSS score is 0.0, but this is likely a placeholder. Based on the vulnerability description, a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N)
• Attack Complexity (AC): Low (L)
• Privileges Required (PR): Low (L) – requires authenticated user
• User Interaction (UI): None (N)
• Scope (S): Unchanged (U)
• Confidentiality (C): None (N) – firewall changes do not directly leak data
• Integrity (I): High (H) – firewall rules can be altered
• Availability (A): Low (L) – could block legitimate traffic

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L Estimated Base Score: 7.1 (High)

Threat Level: High – due to the potential for network segmentation bypass and lateral movement.

Deep Dive & Mechanics

The vulnerability resides in the firewall management function of the Aten PE6208 web interface. The device uses role-based access control (RBAC) to distinguish between administrators and regular users. However, the firewall management endpoint does not properly validate the user's role before processing HTTP POST requests. This allows a low-privileged authenticated user to send a crafted POST request to modify firewall rules, effectively granting them administrative control over network filtering.

Root Cause: The server-side code fails to check the role attribute of the authenticated session when handling firewall configuration changes. The endpoint likely uses a function like update_firewall_rules() that only verifies authentication but not authorization.

Attack Flow:

1. Attacker obtains valid credentials for a low-privileged user (e.g., via phishing or default credentials).
2. Attacker logs into the web interface and captures the session cookie.
3. Attacker sends an HTTP POST request to /cgi-bin/firewall.cgi (or similar) with payload to add/remove firewall rules.
4. The server processes the request without checking if the user is an administrator.
5. Firewall rules are altered, potentially allowing inbound/outbound traffic that was previously blocked.

Vulnerable vs. Patched Code

No patched version is available. The vulnerable code is in the firmware's web server CGI scripts. A hypothetical fix would involve adding a role check before processing firewall changes.

Vulnerable Code (pseudo):

def handle_firewall_post(request):
    if request.user.is_authenticated:
        # Missing role check
        apply_firewall_rules(request.params)
        return "OK"
    else:
        return "Unauthorized"

Patched Code (hypothetical):

def handle_firewall_post(request):
    if request.user.is_authenticated and request.user.role == "admin":
        apply_firewall_rules(request.params)
        return "OK"
    else:
        return "Forbidden"

Exploitation & Lab Setup

Red Team

Prerequisites:

• Access to an Aten PE6208 with firmware 2.3.228 or 2.4.232.
• Valid low-privileged user credentials (e.g., user:password).

Exploitation Steps:

1. Log in to the web interface and capture the session cookie.
2. Use curl to send a malicious POST request to modify firewall rules.

curl -X POST http://<target_ip>/cgi-bin/firewall.cgi \
  -H "Cookie: session=<session_cookie>" \
  -d "action=add&rule=allow&src=0.0.0.0/0&dst=10.0.0.1&port=22"

Expected Outcome: The firewall rule is added, allowing SSH access from any source to a specific internal host.

Blue Team

Detection:

• Monitor for unusual POST requests to /cgi-bin/firewall.cgi from non-admin users.
• Alert on changes to firewall rules via SNMP or syslog.
• Use network traffic analysis to detect unauthorized rule modifications.

Hunting:

• Search logs for firewall.cgi POST requests with parameters like action=add or action=delete.
• Correlate with user role information from authentication logs.

Indicators of Compromise (IOCs)

• Network:
  • HTTP POST requests to /cgi-bin/firewall.cgi from low-privileged user sessions.
  • Unexpected changes in firewall rules (e.g., new allow rules for unusual ports).
• Host:
  • Modified firewall configuration files on the PDU (e.g., /etc/firewall.rules).
  • Log entries showing firewall changes without admin authentication.
• File:
  • firewall.cgi accessed with parameters action=add, action=delete, action=modify.

Detection Engineering

YARA Rule

rule CVE_2023_43847_Firewall_Bypass {
    meta:
        description = "Detects HTTP POST requests to Aten PE6208 firewall.cgi from non-admin users"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-43847"
    strings:
        $post_method = "POST"
        $firewall_cgi = "/cgi-bin/firewall.cgi"
        $action_add = "action=add"
        $action_delete = "action=delete"
    condition:
        $post_method and $firewall_cgi and ($action_add or $action_delete)
}

Sigma Rule

title: CVE-2023-43847 - Aten PE6208 Firewall Bypass via POST
id: 8a9b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP POST requests to firewall.cgi on Aten PE6208 from non-admin users
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/cgi-bin/firewall.cgi'
        cs-uri-query|contains: 'action='
    condition: selection
falsepositives:
    - Legitimate admin actions (should be rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2023-43847 - Aten PE6208 Firewall Bypass Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/cgi-bin/firewall.cgi"; http_uri;
    content:"action="; http_client_body;
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable remote web access to the PDU if not required.
2. Restrict access to the web interface via network ACLs (allow only trusted IPs).
3. Change default credentials and enforce strong passwords for all users.
4. Monitor logs for unauthorized firewall changes.

Long-term Fix:

• No patch available. Contact Aten support for firmware updates.
• Consider replacing the device with a patched alternative if critical.

Workaround:

• Implement a reverse proxy that enforces role-based access control before forwarding requests to the PDU.

Valters IT