Siemens SIMATIC S7-1500 Improper Authentication (CVE-2023-27535)

medium Tenable OT Security Plugin ID 504300

Synopsis

The remote OT asset is affected by a vulnerability.

Description

An authentication bypass vulnerability exists in libcurl <8.0.0 in the FTP connection reuse feature that can result in wrong credentials being used during subsequent transfers. Previously created connections are kept in a connection pool for reuse if they match the current setup. However, certain FTP settings such as CURLOPT_FTP_ACCOUNT, CURLOPT_FTP_ALTERNATIVE_TO_USER, CURLOPT_FTP_SSL_CCC, and CURLOPT_USE_SSL were not included in the configuration match checks, causing them to match too easily. This could lead to libcurl using the wrong credentials when performing a transfer, potentially allowing unauthorized access to sensitive information.

This plugin only works with Tenable.ot.
Please visit https://www.tenable.com/products/tenable-ot for more information.

Solution

The following text was originally created by the Cybersecurity and Infrastructure Security Agency (CISA). The original can be found at CISA.gov.

Siemens has identified the following specific workarounds and mitigations users can apply to reduce risk:

- SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0): Only build and run applications from trusted sources.
Currently no fix is available.
- SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0): Only build and run applications from trusted sources.
Currently no fix is available.
- SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0): Only build and run applications from trusted sources.
Currently no fix is available.
- SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0): Only build and run applications from trusted sources.
Currently no fix is available.
- SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0): Only build and run applications from trusted sources.
Currently no fix is available.

Note: This SSA advises vulnerabilities for firmware version V3.1 only; for versions prior to V3.1 refer to SiemensSecurity Bulletin SSB-439005.

As a general security measure, Siemens recommends protecting network access to devices with appropriate mechanisms. To operate the devices in a protected IT environment, Siemens recommends configuring the environment according to Siemens' operational guidelines for industrial security and following recommendations in the product manuals.

Additional information on industrial security by Siemens can be found on the Siemens industrial security webpage.

For more information see the associated Siemens security advisory SSA-398330 in HTML and CSAF.

Plugin Details

Severity: Medium

ID: 504300

File Name: tenable_ot_siemens_CVE-2023-27535.nasl

Version: 1.3

Type: remote

Family: Tenable.ot

Published: 11/13/2025

Updated: 3/5/2026

Supported Sensors: Tenable OT Security

Risk Information

VPR

Risk Factor: Medium

Score: 4.4

CVSS v3

Risk Factor: Medium

Base Score: 5.9

Temporal Score: 5.3

Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Temporal Vector: CVSS:3.0/E:P/RL:O/RC:C

Vulnerability Information

CPE: cpe:/o:siemens:scalance_xrm334_%2824_v_dc%2c_8xfo%29_firmware:2.4, cpe:/o:siemens:simatic_s7-1500_cpu_firmware:3.1.5, cpe:/o:siemens:scalance_xrm334_%28230_v_ac%2c_8xfo%29_firmware:2.4, cpe:/o:siemens:scalance_xrm334_%28230_v_ac%2c_12xfo%29_firmware:2.4, cpe:/o:siemens:scalance_xrh334_%2824_v_dc%2c_8xfo%2c_cc%29_firmware:2.4, cpe:/o:siemens:scalance_xcm332_firmware:2.4, cpe:/o:siemens:scalance_xrm334_%2824_v_dc%2c_12xfo%29_firmware:2.4, cpe:/o:siemens:scalance_xrm334_%282x230_v_ac%2c_12xfo%29_firmware:2.4, cpe:/o:siemens:scalance_xcm328_firmware:2.4, cpe:/o:siemens:scalance_xcm324_firmware:2.4, cpe:/o:siemens:scalance_xrm334_%282x230_v_ac%2c_8xfo%29_firmware:2.4, cpe:/o:siemens:scalance_xch328_firmware:2.4, cpe:/o:siemens:siplus_s7-1500_cpu_firmware:3.1.5

Required KB Items: Tenable.ot/Siemens

Exploit Ease: No known exploits are available

Patch Publication Date: 12/12/2023

Vulnerability Publication Date: 12/12/2023

Reference Information

CVE: CVE-2023-27535

CWE: 287

ICSA: 23-348-10

Detections

Analytics