CVE-2025-39813 Cert Portal CVE debrief

Who should care

Administrators and operators responsible for the affected Siemens SIMATIC CN 4100 environment, as well as Linux kernel maintainers and system owners who rely on ftrace/trace_pipe functionality in impacted builds.

Technical summary

The supplied description says ftrace_dump_one() can race with concurrent trace_pipe readers. If ring buffer data is consumed between trace_empty() and trace_find_next_entry_inc(), the iterator may be reset so that iter.seq.len and iter.seq.size are both 0, while trace_find_next_entry_inc() returns NULL and leaves iter.seq unpopulated. A subsequent trace_printk_seq() call then meets WARN_ON_ONCE(s->seq.len >= s->seq.size), producing a warning. The fix is to move trace_printk_seq() into the block that only executes when trace_find_next_entry_inc() returns non-NULL.

Defensive priority

Medium. The issue is local, affects availability, and can produce kernel warnings rather than confidentiality or integrity compromise. It still deserves prompt patching in operational environments because repeated warnings can affect stability and noisy logs may complicate incident response.

Recommended defensive actions

• Update to V5.0 or later, as stated in the supplied remediation.
• Review the Siemens ProductCERT and CISA advisory references for the exact affected build scope.
• If you operate affected systems, validate whether trace_pipe/ftrace functionality is in use and prioritize maintenance windows for patching.
• Monitor kernel logs for repeated WARN_ON_ONCE activity around ftrace/trace_printk_seq while remediation is being planned.

Evidence notes

The source corpus describes a race in Linux kernel ftrace: concurrent ftrace_dump_one() and trace_pipe reading can cause trace_find_next_entry_inc() to return NULL after trace_iterator_reset() has zeroed the sequence length and size, which in turn can trip WARN_ON_ONCE() in trace_printk_seq(). The supplied remediation is to move trace_printk_seq() inside the non-NULL branch. The advisory metadata ties the issue to Siemens SIMATIC CN 4100 versions <5.0 and gives a Medium CVSS score of 5.5 (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H).

Official resources