CVE-2023-7339

Executive Summary

CVE-2023-7339 is a stack-based buffer overflow vulnerability (CWE-121) affecting multiple Softing Industrial Automation GmbH gateway products, including pnGate, epGate, mbGate, smartLink HW-DP, and smartLink HW-PN. The vulnerability allows an unauthenticated attacker to overflow buffers via network requests, potentially leading to denial of service (DoS) or remote code execution (RCE). With a CVSS score of 6.5 (Medium), the flaw is exploitable over the network without authentication, but no public proof-of-concept (PoC) or exploit code has been released. The vendor has not confirmed a patch, leaving affected systems at risk.

Note: This vulnerability is not related to any package ecosystem (NPM, PyPI, Go, Ruby) and is specific to industrial control system (ICS) gateways.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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) – Impact confined to the vulnerable component.
• Confidentiality Impact: None (C:N) – No data exposure.
• Integrity Impact: None (I:N) – No data modification.
• Availability Impact: High (A:H) – Likely causes denial of service or system crash.

Threat Level: Medium. While no public exploit exists, the vulnerability is remotely exploitable and affects critical ICS infrastructure. The lack of a patch increases risk for unpatched systems.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in Softing gateways. The affected products (pnGate, epGate, mbGate, smartLink HW-DP, smartLink HW-PN) are used to bridge industrial protocols (e.g., PROFINET, EtherNet/IP, Modbus TCP) to IT networks. The flaw resides in the handling of specially crafted network packets, likely during protocol parsing or data processing.

Root Cause: The software fails to validate the length of incoming data before copying it to a fixed-size stack buffer. An attacker can send a packet with a payload exceeding the buffer size, overwriting adjacent memory (e.g., return addresses, function pointers). This can lead to:

• Denial of Service (DoS): Overwriting critical data causes a crash.
• Remote Code Execution (RCE): With careful crafting, an attacker can redirect execution to arbitrary code.

Attack Vector: The vulnerability is exploitable over the network via the gateway’s listening ports (e.g., TCP 502 for Modbus, TCP 80 for web interfaces). No authentication is required, making it accessible to any network-connected attacker.

Impact: Successful exploitation could allow an attacker to take control of the gateway, disrupt industrial processes, or pivot to other OT devices. Given the criticality of these gateways in manufacturing and energy sectors, the risk is significant.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, based on the vulnerability type, the fix would involve:

• Vulnerable Code (Hypothetical):

  char buffer[256];
  recv(socket, buffer, packet_length, 0); // No length check
  

• Patched Code (Hypothetical):

  char buffer[256];
  if (packet_length > sizeof(buffer)) {
      // Handle error
      return -1;
  }
  recv(socket, buffer, packet_length, 0);
  

The patched version would include bounds checking before copying data to the stack buffer.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A vulnerable Softing gateway (e.g., pnGate v1.30) on the same network.
• Python 3 with socket library.

Exploit Concept: Send a crafted packet with a payload exceeding the buffer size to trigger the overflow. Since no public exploit exists, this is a theoretical example.

import socket

target_ip = "192.168.1.100"
target_port = 502  # Modbus TCP port

# Crafted payload: 300 bytes of 'A' followed by a return address
payload = b"A" * 300 + b"\xef\xbe\xad\xde"  # Example overwrite

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, target_port))
sock.send(payload)
sock.close()

Note: This is a simplified example. Real exploitation would require reverse engineering the binary to find the exact offset and a valid return address.

Blue Team (Defensive)

Detection:

• Monitor for unusually large packets on ports 502, 80, and other gateway ports.
• Use network intrusion detection systems (NIDS) to flag patterns of repeated data (e.g., long strings of 'A').
• Enable logging on gateways and correlate with network traffic.

Mitigation:

• Isolate gateways on a separate VLAN with strict firewall rules.
• Disable unused services and ports.
• Apply vendor patches when available.

Indicators of Compromise (IOCs)

• Network IOCs:

  • Packets with payloads exceeding 256 bytes on TCP ports 502, 80, 443, or 44818.
  • Repeated patterns of non-printable characters in network traffic.
  • Connections from unknown IPs to gateway management interfaces.

• Host IOCs:

  • Unexpected crashes or reboots of the gateway.
  • Log entries indicating buffer overflow errors (e.g., "Stack overflow detected").
  • Unusual processes or memory usage on the gateway.

• File IOCs:

  • Modified firmware files or configuration changes.
  • Presence of unknown binaries or scripts on the gateway.

Detection Engineering

YARA Rule

rule CVE_2023_7339_Softing_Overflow {
    meta:
        description = "Detects potential exploitation of CVE-2023-7339 in Softing gateways"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2023-7339"
    strings:
        $overflow_pattern = { 41 41 41 41 41 41 41 41 } // 8 consecutive 'A's
        $modbus_header = { 00 00 00 00 00 02 } // Modbus TCP header
    condition:
        $modbus_header at 0 and #overflow_pattern > 10
}

Sigma Rule

title: CVE-2023-7339 Softing Gateway Buffer Overflow Attempt
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects network traffic indicative of exploitation of CVE-2023-7339
author: Valters IT
date: 2025-04-10
logsource:
    category: network
    product: suricata
detection:
    selection:
        dest_port:
            - 502
            - 80
            - 443
        payload_length: > 256
    condition: selection
falsepositives:
    - Legitimate large firmware updates
level: high

Suricata Rule

alert tcp any any -> any 502 (msg:"CVE-2023-7339 Softing Gateway Buffer Overflow Attempt"; flow:to_server; content:"|00 00 00 00 00 02|"; depth:6; byte_test:2,>,256,6; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Network Segmentation: Place Softing gateways on isolated OT networks with strict firewall rules.
2. Access Control: Restrict access to gateway management interfaces to trusted IPs only.
3. Monitor Traffic: Deploy NIDS rules (e.g., Suricata) to detect oversized packets.
4. Disable Unused Services: Turn off unnecessary protocols and ports on the gateway.

Long-Term Fix:

• Vendor Patch: Contact Softing for a firmware update. If unavailable, consider replacing the gateway with a patched alternative.
• Firmware Hardening: Apply vendor-recommended security configurations.
• Regular Audits: Conduct periodic vulnerability scans of OT assets.

Workaround: If patching is not possible, use a network firewall to block untrusted traffic to the gateway and implement deep packet inspection (DPI) to filter anomalous payloads.

Valters IT

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