# CVE-2026-23403 — Linux

> As of 2026-05-11, CVE-2026-23403 is a MEDIUM-severity vulnerability in Linux, CVSS v3.1 5.5, EPSS 0.1% (6.6th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-23403, most recently “Linux Kernel LPE Surge: Copy Fail (CVE-2026-31431), Dirty Frag/Fragnesia (CVE-2026-43284/CVE-2026-43500/CVE-2026-46300), and CrackArmor AppArmor Flaws vs. Defense-in-Depth Mitigations”.

**Last updated:** 2026-05-11

## What is CVE-2026-23403?

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.

The record classifies CVE-2026-23403 under weakness class [CWE-401](https://intel.threadlinqs.com/cwe/CWE-401). Its CVSS v3 base vector states that the flaw requires local access to the host, needs low-privilege credentials, needs no user interaction, and has high impact on availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 207 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 5.5 — MEDIUM (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **EPSS (FIRST):** 0.1% probability of exploitation in the next 30 days, higher than 6.6% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 3/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-04-01, last modified 2026-05-11

## Is CVE-2026-23403 being exploited?

It currently carries a trending score of 7 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [Linux](https://intel.threadlinqs.com/vendors/linux): Linux

## How to fix CVE-2026-23403

The record marks a vendor fix as available for CVE-2026-23403. Patch reference: [https://git.kernel.org/stable/c/42fd831abfc15d0643c14688f0522556b347e7e6](https://git.kernel.org/stable/c/42fd831abfc15d0643c14688f0522556b347e7e6). Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.

## Threat activity tracking CVE-2026-23403

1 tracked threat in the Threadlinqs corpus references CVE-2026-23403, either in the campaign’s CVE list or as an indicator on the campaign record.

- [Linux Kernel LPE Surge: Copy Fail (CVE-2026-31431), Dirty Frag/Fragnesia (CVE-2026-43284/CVE-2026-43500/CVE-2026-46300), and CrackArmor AppArmor Flaws vs. Defense-in-Depth Mitigations](https://intel.threadlinqs.com/threat/TL-2026-2424) — HIGH · 2026-05-29

## Sources

Enriched from CVE.org, NVD, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-10-10. This product uses the NVD API but is not endorsed or certified by the NVD.

**Other references**

- [git.kernel.org](https://git.kernel.org/stable/c/9d678eb0fe55c9195d9a253e8c5b82a87b930737)
- [git.kernel.org (6b79abcb3c985e153fcf9d395e1d4336081aabc2)](https://git.kernel.org/stable/c/6b79abcb3c985e153fcf9d395e1d4336081aabc2)
- [git.kernel.org (bcf82c0c5a8b383fd2d5d8f3fd880cdcab2ac557)](https://git.kernel.org/stable/c/bcf82c0c5a8b383fd2d5d8f3fd880cdcab2ac557)
- [git.kernel.org (663ce34786e759ebcbeb3060685c20bcc886d51a)](https://git.kernel.org/stable/c/663ce34786e759ebcbeb3060685c20bcc886d51a)
- [git.kernel.org (786e2c2a87d9c505f33321d1fd23a176aa8ddeb1)](https://git.kernel.org/stable/c/786e2c2a87d9c505f33321d1fd23a176aa8ddeb1)

_Showing 5 of 8 recorded references._

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-23403
Full detection coverage and IOCs for threats exploiting CVE-2026-23403 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp