Siemens SIMATIC S7-1500 TM MFP Improper Input Validation (CVE-2026-46113)

high Tenable OT Security Plugin ID 506254

Synopsis

The remote OT asset is affected by a vulnerability.

Description

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

KVM: x86: Fix shadow paging use-after-free due to unexpected GFN

The shadow MMU computes GFNs for direct shadow pages using sp->gfn plus the SPTE index. This assumption breaks for shadow paging if the guest page tables are modified between VM entries (similar to commit aad885e77496, 'KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE', 2026-03-27). The flow is as follows:

- a PDE is installed for a 2MB mapping, and a page in that area is accessed. KVM creates a kvm_mmu_page consisting of 512 4KB pages;
the kvm_mmu_page is marked by FNAME(fetch) as direct-mapped because the guest's mapping is a huge page (and thus contiguous).

- the PDE mapping is changed from outside the guest.

- the guest accesses another page in the same 2MB area. KVM installs a new leaf SPTE and rmap entry; the SPTE uses the 'correct' GFN (i.e. based on the new mapping, as changed in the previous step) but that GFN is outside of the [sp->gfn, sp->gfn + 511] range; therefore the rmap entry cannot be found and removed when the kvm_mmu_page is zapped.

- the memslot that covers the first 2MB mapping is deleted, and the kvm_mmu_page for the now-invalid GPA is zapped. However, rmap_remove() only looks at the [sp->gfn, sp->gfn + 511] range established in step 1, and fails to find the rmap entry that was recorded by step 3.

- any operation that causes an rmap walk for the same page accessed by step 3 then walks a stale rmap and dereferences a freed kvm_mmu_page.
This includes dirty logging or MMU notifier invalidations (e.g., from MADV_DONTNEED).

The underlying issue is that KVM's walking of shadow PTEs assumes that if a SPTE is present when KVM wants to install a non-leaf SPTE, then the existing kvm_mmu_page must be for the correct gfn. Because the only way for the gfn to be wrong is if KVM messed up and failed to zap a SPTE...
which shouldn't happen, but *actually* only happens in response to a guest write.

That bug dates back literally forever, as even the first version of KVM assumes that the GFN matches and walks into the 'wrong' shadow page.
However, that was only an imprecision until 2032a93d66fa ('KVM: MMU:
Don't allocate gfns page for direct mmu pages') came along.

Fix it by checking for a target gfn mismatch and zapping the existing SPTE. That way the old SP and rmap entries are gone, KVM installs the rmap in the right location, and everyone is happy.

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: High

ID: 506254

File Name: tenable_ot_siemens_CVE-2026-46113.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: High

Score: 7.7

Percentile: 98.94

CVSS v3

Risk Factor: High

Base Score: 8.8

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/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-2026-46113

CWE: 20

Detections

Analytics