CVE-2025-21766Network attack vector

Kernel crash via unprotected PMTU namespace access

Published Feb 27, 2025 · Updated Aug 5, 2026

Use-after-free in Linux IPv4 route handling allows remote attackers to crash or corrupt the kernel with crafted ICMP PMTU traffic. __ip_rt_update_pmtu() reads dst->dev's network namespace before entering an RCU read-side critical section, allowing teardown to free it before fib_lookup() uses it. Exploitation requires a race with network-namespace teardown; successful triggering can panic the system or corrupt kernel routing state.

CVSS severity8.1
High
EPSS probability0.53%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in Linux IPv4 route handling allows remote attackers to crash or corrupt the kernel with crafted ICMP PMTU traffic. __ip_rt_update_pmtu() reads dst->dev's network namespace before entering an RCU read-side critical section, allowing teardown to free it before fib_lookup() uses it. Exploitation requires a race with network-namespace teardown; successful triggering can panic the system or corrupt kernel routing state.

The record

CVE
CVE-2025-21766
Published
Feb 27, 2025
Updated
Aug 5, 2026
Vendor
Siemens
Product
SIPLUS S7-1500 CPU 1518-4 PN/DP MFP
Classifications
CWE-20, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 27, 2025CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 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=V3.1.5 <*

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Siemens · SIPLUS S7-1500 CPU 1518-4 PN/DP MFPversion=V3.1.5 <*
The Linux Kernel Organization · Linuxversion=2b1be6c925cdf4638811765a9160796291494b89; version=2fbc6e89b2f1403189e624cabaf73e189c5e50c6 <139512191bd06f1b496117c76372b2ce372c9a41; version=2fbc6e89b2f1403189e624cabaf73e189c5e50c6 <4583748b65dee4d61bd50a2214715b4237bc152a; version=2fbc6e89b2f1403189e624cabaf73e189c5e50c6 <9b1766d1ff5fe496aabe9fc5f4e34e53f35c11c4; version=2fbc6e89b2f1403189e624cabaf73e189c5e50c6 <a39f61d212d822b3062d7f70fa0588e50e55664e; version=2fbc6e89b2f1403189e624cabaf73e189c5e50c6 <ce3c6165fce0f06305c806696882a3ad4b90e33f; version=2fbc6e89b2f1403189e624cabaf73e189c5e50c6 <ea07480b23225942208f1b754fea1e7ec486d37e; version=4.14.200 <4.15; version=4.19.148 <4.20; version=5.4.68 <5.5; version=5.8.12 <5.9; version=5.9; version=860e2cc78c697c95bc749abb20047239fa1722ea; version=98776a365da509ad923083ae54b38ee521c52742; version=f415c264176e6095e9dee823e09c5bdd0ee0d337
Siemens · SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPversion=V3.1.5 <*
Siemens · SIMATIC S7-1500 CPU 1518-4 PN/DP MFPversion=V3.1.5 <*

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5Siemens ProductCERTCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
8.1LinuxCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
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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