# CVE-2026-72183: landlock: Fix LANDLOCK_SCOPE_SIGNAL bypass on the SIGIO path

> A sandboxed process can bypass Landlock signal restrictions to kill or signal non-sandboxed processes via the SIGIO path.

- **Severity:** High 8.4 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H`)
- **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:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-72183, DEBIAN-CVE-2026-72183, GHSA-5hcp-6cc5-jgx7, UBUNTU-CVE-2026-72183

## What is CVE-2026-72183?

CVE-2026-72183 is a high-severity vulnerability in Linux, published on 15 Aug 2026. 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:

landlock: Fix LANDLOCK_SCOPE_SIGNAL bypass on the SIGIO path

LANDLOCK_SCOPE_SIGNAL must prevent a sandboxed process from signaling
processes outside its Landlock domain.  It can be bypassed through the
asynchronous SIGIO delivery path.

A sandboxed process that owns any file or socket can arm it with
fcntl(fd, F_SETOWN, -pgid), fcntl(fd, F_SETSIG, SIGKILL) and O_ASYNC, so
that an I/O event makes the kernel deliver the chosen signal to the
whole process group.  As the head of its process group's task list (the
default position right after fork()) that group can also hold the
non-sandboxed process that launched it, e.g. a supervisor or a security
monitor.  The sandbox can thus kill or signal the processes
LANDLOCK_SCOPE_SIGNAL is meant to protect from it.

The scope is enforced in hook_file_send_sigiotask() against the Landlock
domain recorded at F_SETOWN time, not the live domain of the sender.
control_current_fowner() decides whether to record that domain and skips
recording it when the fowner target is in the caller's thread group,
which is safe only for a single-task target (PIDTYPE_PID, PIDTYPE_TGID).
For a process group (PIDTYPE_PGID) pid_task() returns only one member;
recording is skipped whenever that member shares the caller's thread
group, and hook_file_send_sigiotask() then lets the signal fan out to
the whole group unchecked.

Record the domain for every non single-process target so the scope is
enforced against each group member at delivery time.

That recording is necessary but not sufficient on its own: the kernel
signals a process group through its members' thread-group leaders, and
the leader of the registrant's own process can carry a different
Landlock domain than the sibling thread that armed the owner.
domain_is_scoped() would then deny that leader, even though commit
18eb75f3af40 ("landlock: Always allow signals between threads of the
same process") requires same-process delivery to be allowed.
hook_task_kill() avoids this by evaluating same_thread_group() live, per
recipient; the SIGIO path instead delegates the whole decision to a
single registration-time check, which a process-group fan-out cannot
honor.

So also record the registrant's thread group next to its domain and
exempt it at delivery: hook_file_send_sigiotask() allows the signal
whenever the recipient belongs to the registrant's own process,
restoring the same-process guarantee while keeping out-of-domain group
members blocked.  The direct kill() path (hook_task_kill) already
evaluates the live domain and is unaffected.

[mic: Check pid_type earlier and improve comment, fix commit message,
fix comment formatting]

## Which versions are affected by CVE-2026-72183?


## How do I fix CVE-2026-72183?

Apply the vendor's patch.

## Is CVE-2026-72183 being exploited?

There is no known exploitation of CVE-2026-72183 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72183 and fix it if it is affected.

What it is: CVE-2026-72183 is a high-severity vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-72183 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-72183/ (Markdown: https://insights.sbomify.com/CVE-2026-72183/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72183
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72183
- OSV: https://osv.dev/vulnerability/CVE-2026-72183

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72183/
Summaries are generated and may contain mistakes; the official description above is the record.