Siemens SIMATIC S7-1500 CPU 1518 MFP Improper Update of Reference Count (CVE-2025-38732)

medium Tenable OT Security Plugin ID 505655

Synopsis

The remote OT asset is affected by a vulnerability.

Description

In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_reject: don't leak dst refcount for loopback packets recent patches to add a WARN() when replacing skb dst entry found an old bug: WARNING: include/linux/skbuff.h:1165 skb_dst_check_unset include/linux/skbuff.h:1164 [inline] WARNING:
include/linux/skbuff.h:1165 skb_dst_set include/linux/skbuff.h:1210 [inline] WARNING: include/linux/skbuff.h:1165 nf_reject_fill_skb_dst+0x2a4/0x330 net/ipv4/netfilter/nf_reject_ipv4.c:234 [..] Call Trace:
nf_send_unreach+0x17b/0x6e0 net/ipv4/netfilter/nf_reject_ipv4.c:325 nft_reject_inet_eval+0x4bc/0x690 net/netfilter/nft_reject_inet.c:27 expr_call_ops_eval net/netfilter/nf_tables_core.c:237 [inline] ..
This is because blamed commit forgot about loopback packets. Such packets already have a dst_entry attached, even at PRE_ROUTING stage.
Instead of checking hook just check if the skb already has a route attached to it.

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: 505655

File Name: tenable_ot_siemens_CVE-2025-38732.nasl

Version: 1.1

Type: Remote

Family: Tenable.ot

Published: 7/27/2026

Updated: 7/27/2026

Supported Sensors: Tenable OT Security

Risk Information

VPR

Risk Factor: Low

Score: 3

Percentile: 23.37

CVSS v3

Risk Factor: Medium

Base Score: 5.8

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

Vulnerability Information

CPE: cpe:/o:siemens:simatic_s7-1500_cpu_firmware:3.1.6, cpe:/o:siemens:siplus_s7-1500_cpu_firmware

Required KB Items: Tenable.ot/Siemens

Exploit Ease: No known exploits are available

Patch Publication Date: 5/12/2026

Vulnerability Publication Date: 9/5/2025

Reference Information

CVE: CVE-2025-38732

CWE: 911

Detections

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