Siemens SIMATIC S7-1500 TM MFP Improper Resource Locking (CVE-2026-23356)

medium Tenable OT Security Plugin ID 506399

Synopsis

The remote OT asset is affected by a vulnerability.

Description

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

drbd: fix 'LOGIC BUG' in drbd_al_begin_io_nonblock()

Even though we check that we 'should' be able to do lc_get_cumulative() while holding the device->al_lock spinlock, it may still fail, if some other code path decided to do lc_try_lock() with bad timing.

If that happened, we logged 'LOGIC BUG for enr=...', but still did not return an error.

The rest of the code now assumed that this request has references for the relevant activity log extents.

The implcations are that during an active resync, mutual exclusivity of resync versus application IO is not guaranteed. And a potential crash at this point may not realizs that these extents could have been target of in-flight IO and would need to be resynced just in case.

Also, once the request completes, it will give up activity log references it does not even hold, which will trigger a BUG_ON(refcnt == 0) in lc_put().

Fix:

Do not crash the kernel for a condition that is harmless during normal operation: also catch 'e->refcnt == 0', not only 'e == NULL' when being noisy about 'al_complete_io() called on inactive extent %u\\n'.

And do not try to be smart and 'guess' whether something will work, then be surprised when it does not.
Deal with the fact that it may or may not work. If it does not, remember a possible 'partially in activity log' state (only possible for requests that cross extent boundaries), and return an error code from drbd_al_begin_io_nonblock().

A latter call for the same request will then resume from where we left off.

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: Medium

ID: 506399

File Name: tenable_ot_siemens_CVE-2026-23356.nasl

Version: 1.2

Type: Remote

Family: Tenable.ot

Published: 10/20/2026

Updated: 10/21/2026

Supported Sensors: Tenable OT Security

Risk Information

VPR

Risk Factor: Low

Score: 3

Percentile: 23.67

CVSS v2

Risk Factor: Medium

Base Score: 4.6

Temporal Score: 3.4

Vector: CVSS2#AV:L/AC:L/Au:S/C:N/I:N/A:C

CVSS Score Source: CVE-2026-23356

CVSS v3

Risk Factor: Medium

Base Score: 5.5

Temporal Score: 4.8

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

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

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-2026-23356

CWE: 413

Detections

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