CVE-2025-39813: Debian Linux

Medium severity, CVSS 4.7. EPSS: 0.1% chance of exploitation in the next 30 days.

In the Linux kernel, the following vulnerability has been resolved: ftrace: Fix potential warning in trace_printk_seq during ftrace_dump When calling ftrace_dump_one() concurrently with reading trace_pipe, a WARN_ON_ONCE() in trace_printk_seq() can be triggered due to a race condition. The issue occurs because: CPU0 (ftrace_dump) CPU1 (reader) echo z > /proc/sysrq-trigger !trace_empty(&iter) trace_iterator_reset(&iter) <- len = size = 0 cat /sys/kernel/tracing/trace_pipe trace_find_next_entry_inc(&iter) __find_next_entry ring_buffer_empty_cpu <- all empty return NULL trace_printk_seq(&iter.seq) WARN_ON_ONCE(s->seq.len >= s->seq.size) In the context between trace_empty() and trace_find_next_entry_inc() during ftrace_dump, the ring buffer data was consumed by other readers. This caused trace_find_next_entry_inc to return NULL, failing to populate `iter.seq`. At this point, due to the prior trace_iterator_reset, both `iter.seq.len` and `iter.seq.size` were set to 0. Since they are equal, the WARN_ON_ONCE condition is triggered. Move the trace_printk_seq() into the if block that checks to make sure the return value of trace_find_next_entry_inc() is non-NULL in ftrace_dump_one(), ensuring the 'iter.seq' is properly populated before subsequent operations.

Affected products

• Debian Debian Linux: version 11.0 only
• Linux Linux Kernel: from 2.6.28, before 5.4.298 (fixed in 5.4.298); from 5.5, before 5.10.242 (fixed in 5.10.242); from 5.11, before 5.15.191 (fixed in 5.15.191); from 5.16, before 6.1.150 (fixed in 6.1.150); from 6.2, before 6.6.104 (fixed in 6.6.104); from 6.7, before 6.12.45 (fixed in 6.12.45); …

Published 2025-09-16. Last modified 2026-06-17.