CVE-2025-39782 Cert Portal CVE debrief

Who should care

Asset owners, operators, and maintenance teams responsible for Siemens SIMATIC CN 4100 systems identified in the advisory, especially environments that can trigger ext4/jbd2 writeback activity. Because the impact is availability-only, availability-sensitive deployments should prioritize validation and patching.

Technical summary

The advisory says both jbd2_log_do_checkpoint() and jbd2_journal_shrink_checkpoint_list() periodically release j_list_lock during batch processing, but only the latter explicitly calls cond_resched() when need_resched() is true. jbd2_log_do_checkpoint() instead relies on potentially sleeping paths such as __flush_batch() or wait_on_buffer() to yield. If those paths do not sleep, the kernel can remain busy long enough to hit a watchdog soft lockup. The reported stack trace shows the issue during writeback and ext4 journal handling, and the CVSS vector is AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

Defensive priority

Medium to high for affected Siemens assets because the impact is a kernel soft lockup and service interruption, not code execution or data corruption. Treat as a priority availability fix where the affected product/version is present.

Recommended defensive actions

• Update affected Siemens SIMATIC CN 4100 systems to V5.0 or later, as directed in the vendor remediation.
• Confirm whether the deployed product and version match the advisory scope before and after patching.
• Review maintenance windows and test the update on a representative system before fleet-wide rollout.
• Monitor affected systems for watchdog or soft-lockup messages during writeback-heavy workloads while remediation is planned.

Evidence notes

The source advisory (ICSA-26-134-10 / SSA-032379) describes a Linux kernel jbd2 softlockup condition and lists remediation as updating to V5.0 or later. The advisory metadata records publication on 2026-05-12 and republication on 2026-05-14. The CVSS vector provided is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, which supports an availability-focused assessment. The vendor/product mapping in the supplied source is low confidence and marked needsReview, so the Siemens product scope should be validated against the official Siemens advisory.

Official resources