Full Report
Affected products incorrectly validate TCP sequence numbers. This could allow an unauthenticated remote attacker to create a denial of service condition by injecting spoofed TCP RST packets. Siemens recommends countermeasures for products where fixes are not, or not yet available.
Analysis Summary
# Vulnerability: TCP Sequence Number Validation Vulnerability in Siemens CP343-1
## CVE Details
- **CVE ID:** CVE-2023-51440
- **CVSS Score:** 7.5 (High) via CVSS v3.1 / 8.7 (High) via CVSS v4.0
- **CWE:** CWE-940: Improper Verification of Source of a Communication Channel
## Affected Systems
- **Products:**
- SIMATIC CP 343-1 (6GK7343-1EX30-0XE0)
- SIMATIC CP 343-1 Lean (6GK7343-1CX10-0XE0)
- SIPLUS NET CP 343-1 (6AG1343-1EX30-7XE0)
- SIPLUS NET CP 343-1 Lean (6AG1343-1CX10-2XE0)
- **Versions:** All versions are currently affected.
- **Configurations:** Devices utilizing the TCP/IP stack for Ethernet communication on SIMATIC S7-300 platforms.
## Vulnerability Description
The TCP/IP stack implementation in the affected communication processors fails to correctly validate TCP sequence numbers. This flaw allows a remote, unauthenticated attacker to predict or bypass sequence number checks to inject spoofed TCP RST (Reset) packets into existing sessions.
## Exploitation
- **Status:** PoC available (indicated by CVSS "Exploit Code Maturity: Proof-of-Concept" - E:P)
- **Complexity:** Low
- **Attack Vector:** Network
## Impact
- **Confidentiality:** None
- **Integrity:** None
- **Availability:** High (Denial of Service via terminated TCP connections)
## Remediation
### Patches
- **No patches currently available:** Siemens has stated that no fixes are currently planned for these specific legacy communication processors.
### Workarounds
- **Network Segmentation:** Implement strict network segmentation to ensure only trusted devices can communicate with the CP 343-1 modules.
- **Defense-in-Depth:** Follow Siemens' Industrial Security operational guidelines to reduce the exposure of vulnerable devices to the open network.
- **Access Control:** Restrict network access to the devices to the minimum necessary for operation.
## Detection
- **Indicators of Compromise:** Unusual or frequent TCP connection resets occurring without legitimate network errors or administrative action.
- **Detection methods and tools:**
- Network Intrusion Detection Systems (NIDS) can be configured to monitor for anomalous TCP RST packets or sequence number mismatches.
- Deep Packet Inspection (DPI) of industrial traffic to identify spoofed traffic patterns.
## References
- **Vendor Advisory:** hxxps[://]cert-portal[.]siemens[.]com/productcert/html/ssa-516818[.]html
- **Siemens Industrial Security Guidelines:** hxxps[://]www[.]siemens[.]com/cert/operational-guidelines-industrial-security
- **Siemens ProductCERT:** hxxps[://]www[.]siemens[.]com/cert/advisories