# CVE-2026-74342: kernfs: link kn to its parent before the LSM init hook

> A null pointer dereference in the Linux kernel's kernfs subsystem allows local attackers to cause a system crash via cgroup operations on SELinux-enabled systems.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** AZL-96507, BELL-CVE-2026-74342, DEBIAN-CVE-2026-74342, GHSA-c5w7-7j2g-7v27, UBUNTU-CVE-2026-74342

## What is CVE-2026-74342?

CVE-2026-74342 is a 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:

kernfs: link kn to its parent before the LSM init hook

After commit 12e9e3cd03b5 ("simpe_xattr: use per-sb cache"),
kernfs_xattr_set() and kernfs_xattr_get() compute the cache via
kernfs_root(kn) before any other check.  kernfs_root(kn) walks
kn->__parent first and falls back to kn->dir.root, both of which are
NULL on a freshly kmem_cache_zalloc()'d kn. kn->__parent was being set
in kernfs_new_node() after __kernfs_new_node() returned, and kn->dir.root
is set even later by kernfs_create_dir_ns() / kernfs_create_empty_dir().

The LSM kernfs_init_security hook is invoked from inside
__kernfs_new_node(), before either field has been initialized.
selinux_kernfs_init_security() ends with kernfs_xattr_set(kn,
XATTR_NAME_SELINUX, ...).  kernfs_root(kn) then returns NULL, and
&((struct kernfs_root *)NULL)->xa_cache evaluates to
offsetof(struct kernfs_root, xa_cache) which faults:

  BUG: kernel NULL pointer dereference, address: 00000000000000e0
  RIP: 0010:simple_xattr_set+0x27/0x8b0
  Call Trace:
   kernfs_xattr_set+0x63/0xb0
   selinux_kernfs_init_security+0x13b/0x270
   security_kernfs_init_security+0x36/0xc0
   __kernfs_new_node+0x182/0x290
   kernfs_new_node+0x80/0xc0
   kernfs_create_dir_ns+0x2b/0xa0
   cgroup_create+0x116/0x380
   cgroup_mkdir+0x7c/0x1a0

Reproduces deterministically at PID 1 (systemd) on an SELinux-enabled
distro. The first cgroup mkdir under /sys/fs/cgroup with a labelled
parent panics the kernel.

The LSM hook's contract is that the kn_dir argument is the parent of
the new kn, so kn->__parent should already point at kn_dir when the
hook runs.  Move kernfs_get(parent) and rcu_assign_pointer of
kn->__parent from kernfs_new_node() into __kernfs_new_node() right
before the security hook, and unwind the parent reference on the
err_out4 path.  kernfs_root(kn) then takes its parent branch during
the hook and returns parent->dir.root, which is the correct root.

This also closes the same-shape latent bug in kernfs_xattr_get() (which
today is hidden only by kernfs_iattrs_noalloc() returning NULL on a
fresh kn).

## Which versions are affected by CVE-2026-74342?


## How do I fix CVE-2026-74342?

Apply the vendor's patch.

## Is CVE-2026-74342 being exploited?

There is no known exploitation of CVE-2026-74342 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74342 and fix it if it is affected.

What it is: CVE-2026-74342 is a 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-2026-74342 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-2026-74342/ (Markdown: https://insights.sbomify.com/CVE-2026-74342/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74342
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74342
- OSV: https://osv.dev/vulnerability/CVE-2026-74342

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74342/
Summaries are generated and may contain mistakes; the official description above is the record.