CVE-2026-23405 apparmor: fix: limit the number of levels of policy namespaces

What is CVE-2026-23405?

CVE-2026-23405 is a medium-severity denial of service vulnerability in Linux kernel, published on 1 Apr 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:

apparmor: fix: limit the number of levels of policy namespaces

Currently the number of policy namespaces is not bounded relying on the user namespace limit. However policy namespaces aren't strictly tied to user namespaces and it is possible to create them and nest them arbitrarily deep which can be used to exhaust system resource.

Hard cap policy namespaces to the same depth as user namespaces.

Which versions are affected by CVE-2026-23405?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-23405?

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-2026-23405 being exploited?

There is no known exploitation of CVE-2026-23405 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-82019, BELL-CVE-2026-23405, DEBIAN-CVE-2026-23405, GHSA-xwx5-hj9g-f35h, UBUNTU-CVE-2026-23405.