CVE-2025-21834 seccomp: passthrough uretprobe systemcall without filtering
The Linux kernel crashes processes using uretprobes under seccomp filters, causing denial of service for containerized applications.
- 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-2025-21834?
CVE-2025-21834 is a medium-severity denial of service vulnerability in Linux kernel, published on 6 Mar 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:
seccomp: passthrough uretprobe systemcall without filtering
When attaching uretprobes to processes running inside docker, the attached process is segfaulted when encountering the retprobe.
The reason is that now that uretprobe is a system call the default seccomp filters in docker block it as they only allow a specific set of known syscalls. This is true for other userspace applications which use seccomp to control their syscall surface.
Since uretprobe is a "kernel implementation detail" system call which is not used by userspace application code directly, it is impractical and there's very little point in forcing all userspace applications to explicitly allow it in order to avoid crashing tracked processes.
Pass this systemcall through seccomp without depending on configuration.
Note: uretprobe is currently only x86_64 and isn't expected to ever be supported in i386.
[kees: minimized changes for easier backporting, tweaked commit log]
Which versions are affected by CVE-2025-21834?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-21834?
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-2025-21834 being exploited?
There is no known exploitation of CVE-2025-21834 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-21834, DEBIAN-CVE-2025-21834, GHSA-3cmq-72j9-674j, UBUNTU-CVE-2025-21834.