CVE-2025-38468 Siemens CVE debrief

Who should care

Operators and maintainers of the affected Siemens SIMATIC S7-1500 CPU models, especially environments that expose or use the additional GNU/Linux subsystem, interactive shell access, or third-party applications. OT teams should also care because the impact is service disruption rather than data theft, and the vendor advisory states no fix is currently available.

Technical summary

The source advisory describes a Linux kernel path in which HTB dequeue processing interacts with netem and a blackhole child qdisc. When packet backlog is reduced to zero, the selected HTB class can be removed from the red-black tree. If a later dequeue path returns NULL and htb_lookup_leaf is called again on the same empty tree, the existing BUG_ON is reached. The reported fix is to return NULL instead of asserting when the tree is empty.

Defensive priority

High for affected Siemens deployments. The issue is local and requires some level of access, but the consequence is a crash/denial of service in a product family used in industrial control contexts. Because the advisory lists no fix, exposure reduction and access control are the main immediate controls.

Recommended defensive actions

• Confirm whether any listed SIMATIC S7-1500 CPU 1518/1518F MFP variants are in scope in your environment.
• Restrict access to the additional GNU/Linux subsystem shell to trusted personnel only.
• Limit execution of applications and packages to trusted, vetted sources only.
• Review whether traffic-control/qdisc features are needed on affected systems and remove unnecessary local access paths where possible.
• Monitor vendor and CISA advisories for updates, since the source advisory states that no fix is currently available.

Evidence notes

CISA’s CSAF source item and Siemens ProductCERT advisory both identify CVE-2025-38468 and list five affected SIMATIC S7-1500 CPU variants. The advisory text says the Linux kernel bug occurs in htb_lookup_leaf when an empty rbtree is encountered after HTB/netem/blackhole queue handling, leading to a BUG_ON and a denial of service. The remediation section explicitly states that no fix is currently available and recommends restricting shell access and only running trusted applications. The supplied CVSS vector is AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, which aligns with a local availability-impact issue.

Official resources