CVE-2026-23403 apparmor: fix memory leak in verify_header

What is CVE-2026-23403?

CVE-2026-23403 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 memory leak in verify_header

The function sets `*ns = NULL` on every call, leaking the namespace string allocated in previous iterations when multiple profiles are unpacked. This also breaks namespace consistency checking since *ns is always NULL when the comparison is made.

Remove the incorrect assignment. The caller (aa_unpack) initializes *ns to NULL once before the loop, which is sufficient.

Weakness: CWE-401

Which versions are affected by CVE-2026-23403?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-23403?

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-2026-23403 being exploited?

There is no known exploitation of CVE-2026-23403 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-82013, BELL-CVE-2026-23403, DEBIAN-CVE-2026-23403, GHSA-rr4h-g2x9-f96p, UBUNTU-CVE-2026-23403.