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PatchSiren cyber security CVE debrief

CVE-2025-21718 Linux CVE debrief

A use-after-free vulnerability exists in the Linux kernel's ROSE (Radio Amateur) network protocol implementation. The vulnerability occurs when a ROSE timer expires and accesses a socket that has already been freed. This can lead to a denial-of-service (DoS) or potentially allow an attacker to execute arbitrary code. The issue arises from the ROSE timers only acquiring the socket spinlock without checking if the socket is owned by one user thread. To address this, a check has been added to ensure the socket is owned by one user thread and rearm the timers if needed. Evidence is limited to CVE and NVD records, so verification of affected versions and remediation is necessary. System

Vendor
Linux
Product
SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0)
CVSS
HIGH 7
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-14
Original CVE updated
2026-07-28
Advisory published
2026-07-14
Advisory updated
2026-07-28

Who should care

System administrators and security teams responsible for Linux-based systems, especially those using the ROSE protocol, should assess their exposure and verify that their systems are updated with the patched kernel version.

Why it matters

CVE-2025-21718 is a high-severity vulnerability in the Linux kernel's ROSE protocol implementation. Defenders should prioritize patching or mitigating this vulnerability to prevent potential DoS and code execution risks. System administrators and security teams responsible for Linux-based systems, especially those using the ROSE protocol, should assess their exposure and verify that their systems are updated with the patched kernel version. Evidence is limited to CVE and NVD records, so verification of affected versions and remediation is necessary.

  • Denial-of-service (DoS) due to system crashes or freezes
  • Potential arbitrary code execution with elevated privileges
  • Increased risk of lateral movement within networks
  • Need for verification of GNU/Linux subsystem configuration and security

Technical summary

The Linux kernel's ROSE protocol implementation is vulnerable to a use-after-free error. When a ROSE timer expires, it accesses a socket that has already been freed, potentially leading to a denial-of-service (DoS) or arbitrary code execution. The vulnerability has been resolved by adding a check to ensure the socket is owned by one user thread and rearming the timers if needed. This issue highlights the importance of verifying GNU/Linux subsystem configuration and security. Defenders should prioritize patching or mitigating this vulnerability to prevent potential DoS and code execution risks.

Defensive priority

High

Recommended defensive actions

  • Limit access to the interactive shell of the additional GNU/Linux subsystem to trusted personnel only.
  • Only build and run applications from trusted sources.
  • Verify that GNU/Linux subsystem is properly configured and secured
  • Monitor system logs for suspicious activity related to ROSE protocol
  • Review compensating controls for exposed systems while remediation is scheduled and verified.
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented.
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The vulnerability was discovered in the Linux kernel's ROSE protocol implementation. A use-after-free error occurs when a ROSE timer expires and accesses a socket that has already been freed. This issue has been resolved by adding a check to ensure the socket is owned by one user thread and rearming the timers if needed.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-21718 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-21718

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2025-21718 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-21718

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • CVE-2025-21718

    Unverified legacy reference

    URL: https://raw.githubusercontent.com/cisagov/CSAF/develop/csaf_files/OT/white/2026/icsa-26-209-04.json

    cisa_csaf

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/csaf/ssa-019113.json

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/html/ssa-019113.html

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/news-events/ics-advisories/icsa-26-209-04

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/news-events/ics-alerts/ics-alert-10-301-01

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/resources-tools/resources/ics-recommended-practices

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/topics/industrial-control-systems

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/sites/default/files/recommended_practices/NCCIC_ICS-CERT_Defense_in_Depth_2016_S508C.pdf

    Supplemental source

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.