Siemens SIMATIC S7-1500 TM MFP Improper Input Validation (CVE-2026-31705)

critical Tenable OT Security Plugin ID 506347

Synopsis

The remote OT asset is affected by a vulnerability.

Description

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix out-of-bounds write in smb2_get_ea() EA alignment

smb2_get_ea() applies 4-byte alignment padding via memset() after writing each EA entry. The bounds check on buf_free_len is performed before the value memcpy, but the alignment memset fires unconditionally afterward with no check on remaining space.

When the EA value exactly fills the remaining buffer (buf_free_len == 0 after value subtraction), the alignment memset writes 1-3 NUL bytes past the buf_free_len boundary. In compound requests where the response buffer is shared across commands, the first command (e.g., READ) can consume most of the buffer, leaving a tight remainder for the QUERY_INFO EA response. The alignment memset then overwrites past the physical kvmalloc allocation into adjacent kernel heap memory.

Add a bounds check before the alignment memset to ensure buf_free_len can accommodate the padding bytes.

This is the same bug pattern fixed by commit beef2634f81f ('ksmbd: fix potencial OOB in get_file_all_info() for compound requests') and commit fda9522ed6af ('ksmbd: fix OOB write in QUERY_INFO for compound requests'), both of which added bounds checks before unconditional writes in QUERY_INFO response handlers.

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

Solution

Refer to the vendor advisory.

Plugin Details

Severity: Critical

ID: 506347

File Name: tenable_ot_siemens_CVE-2026-31705.nasl

Version: 1.1

Type: Remote

Family: Tenable.ot

Published: 10/20/2026

Updated: 10/20/2026

Supported Sensors: Tenable OT Security

Risk Information

VPR

Risk Factor: Medium

Score: 4.9

Percentile: 58.37

CVSS v3

Risk Factor: Critical

Base Score: 9.8

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

Vulnerability Information

CPE: cpe:/o:siemens:simatic_s7-1500_tm_mfp

Required KB Items: Tenable.ot/Siemens

Exploit Ease: No known exploits are available

Patch Publication Date: 10/13/2026

Vulnerability Publication Date: 10/13/2026

Reference Information

CVE: CVE-2026-31705

CWE: 20

Detections

Analytics