CVE-2025-21938Network attack vector

Remote service interruption via MPTCP endpoint race

Published Apr 1, 2025 · Updated Sep 8, 2026

Race condition in the Linux kernel MPTCP subsystem allows remote attackers to interrupt service via parallel connection requests. mptcp_pm_nl_append_new_local_addr deletes a concurrently inserted implicit address and calls synchronize_rcu while packet reception has preemption disabled. Concurrent MPTCP subflow SYNs trigger the scheduling-while-atomic fault, especially when advertised and internal endpoint addresses differ.

CVSS severity5.9
Medium
EPSS probability0.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Race condition in the Linux kernel MPTCP subsystem allows remote attackers to interrupt service via parallel connection requests. mptcp_pm_nl_append_new_local_addr deletes a concurrently inserted implicit address and calls synchronize_rcu while packet reception has preemption disabled. Concurrent MPTCP subflow SYNs trigger the scheduling-while-atomic fault, especially when advertised and internal endpoint addresses differ.

The record

CVE
CVE-2025-21938
Published
Apr 1, 2025
Updated
Sep 8, 2026
Vendor
Siemens
Product
SIPLUS S7-1500 CPU 1518-4 PN/DP MFP
Classifications
CWE-362, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 1, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

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 vectornetwork
Required privilegesunauthenticated

What is affected?

Siemens · SIPLUS S7-1500 CPU 1518-4 PN/DP MFPversion=V3.1.6 <*
The Linux Kernel Organization · Linuxversion=5.18; version=d045b9eb95a9b611c483897a69e7285aefdc66d7 <022bfe24aad8937705704ff2e414b100cf0f2e1a; version=d045b9eb95a9b611c483897a69e7285aefdc66d7 <125ccafe6dd062901b5a0c31ee9038740fc8859e; version=d045b9eb95a9b611c483897a69e7285aefdc66d7 <4b228dae3d2cc6d9dce167449cd8fa9f028e9376; version=d045b9eb95a9b611c483897a69e7285aefdc66d7 <f1404f368c40fc6a068dad72e4ee0824ee6a78ee; version=d045b9eb95a9b611c483897a69e7285aefdc66d7 <f3fcdb2de9fdbed9d8c6a8eb2c5fbd7d6f54a4d8
Siemens · SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPversion=V3.1.6 <*
Siemens · SIMATIC S7-1500 CPU 1518-4 PN/DP MFPversion=V3.1.6 <*

Published CVSS scores

5.9Siemens ProductCERTCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

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

Weakness, pattern, technique

CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo