CVE-2025-39829 trace/fgraph: Fix the warning caused by missing unregister notifier
A missing unregister notifier in the Linux kernel fgraph tracer can trigger a warning and potential instability when function profiling is toggled.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-39829?
CVE-2025-39829 is a medium-severity denial of service vulnerability in Linux kernel, published on 16 Sep 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
trace/fgraph: Fix the warning caused by missing unregister notifier
This warning was triggered during testing on v6.16:
notifier callback ftrace_suspend_notifier_call already registered WARNING: CPU: 2 PID: 86 at kernel/notifier.c:23 notifier_chain_register+0x44/0xb0 ... Call Trace: <TASK> blocking_notifier_chain_register+0x34/0x60 register_ftrace_graph+0x330/0x410 ftrace_profile_write+0x1e9/0x340 vfs_write+0xf8/0x420 ? filp_flush+0x8a/0xa0 ? filp_close+0x1f/0x30 ? do_dup2+0xaf/0x160 ksys_write+0x65/0xe0 do_syscall_64+0xa4/0x260 entry_SYSCALL_64_after_hwframe+0x77/0x7f
When writing to the function_profile_enabled interface, the notifier was not unregistered after start_graph_tracing failed, causing a warning the next time function_profile_enabled was written.
Fixed by adding unregister_pm_notifier in the exception path.
Which versions are affected by CVE-2025-39829?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-39829?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-39829 being exploited?
There is no known exploitation of CVE-2025-39829 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-71209, BELL-CVE-2025-39829, DEBIAN-CVE-2025-39829, GHSA-qgx7-pghq-36xv, ROOT-OS-DEBIAN-11-CVE-2025-39829, ROOT-OS-DEBIAN-12-CVE-2025-39829 and 3 more.