CVE-2025-38732

Service interruption via loopback route reference leak

Published Sep 5, 2025 · Updated Sep 8, 2026

A netfilter reference-count leak in Linux and affected Siemens firmware allows local users to exhaust kernel resources with loopback rejects. nf_reject_fill_skb_dst replaces an attached dst_entry on loopback packets without releasing the prior reference because it tests the hook instead of route presence. Low-privileged local access and a netfilter reject path handling loopback traffic are required; repeated triggers exhaust route references and interrupt service.

CVSS severity5.5
Medium
EPSS probability0.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A netfilter reference-count leak in Linux and affected Siemens firmware allows local users to exhaust kernel resources with loopback rejects. nf_reject_fill_skb_dst replaces an attached dst_entry on loopback packets without releasing the prior reference because it tests the hook instead of route presence. Low-privileged local access and a netfilter reject path handling loopback traffic are required; repeated triggers exhaust route references and interrupt service.

The record

CVE
CVE-2025-38732
Published
Sep 5, 2025
Updated
Sep 8, 2026
Vendor
Siemens
Product
SIPLUS S7-1500 CPU 1518-4 PN/DP MFP
Classifications
CWE-911, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 5, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=V3.1.6 <*

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Siemens · SIPLUS S7-1500 CPU 1518-4 PN/DP MFPversion=V3.1.6 <*
The Linux Kernel Organization · Linuxversion=5.9; version=f53b9b0bdc59c0823679f2e3214e0d538f5951b9 <51e8531371f90bee742c63775c9a568e5d6bf3c5; version=f53b9b0bdc59c0823679f2e3214e0d538f5951b9 <7b8b503c06274ef3c6c1a107743f1ec0d0a53ef8; version=f53b9b0bdc59c0823679f2e3214e0d538f5951b9 <82ef97abf22790182f7d433c74960dfd61b99c33; version=f53b9b0bdc59c0823679f2e3214e0d538f5951b9 <91a79b792204313153e1bdbbe5acbfc28903b3a5; version=f53b9b0bdc59c0823679f2e3214e0d538f5951b9 <a0a3ace2a57887dac1e7c9a724846040c3e31868; version=f53b9b0bdc59c0823679f2e3214e0d538f5951b9 <b32e1590a8d22cf7d7f965e46d5576051acf8e42; version=f53b9b0bdc59c0823679f2e3214e0d538f5951b9 <b7a885ba25960c91db237c3f83b4285156789bce
Siemens · SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPversion=V3.1.6 <*
Siemens · SIMATIC CN 4100version=0 <V5.0
Siemens · SIMATIC S7-1500 CPU 1518-4 PN/DP MFPversion=V3.1.6 <*

Published CVSS scores

5.5NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.8Siemens ProductCERTCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-911Improper Update of Reference Count
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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