A flaw in the Linux kernel’s XFRM ESP-in-TCP subsystem, named Fragnesia, permits a local attacker to perform arbitrary byte writes to the kernel page cache of read‑only files. This constitutes a local privilege escalation, allowing an attacker to overwrite kernel structures or code sections, potentially leading to full root access. The weakness is a classic type of write‑through vulnerability in kernel memory handling.

All Linux systems running kernel versions that have not yet incorporated the Fragnesia fix are affected. The issue originates in the core XFRM framework and therefore applies across distributions that ship the upstream kernel unchanged, unless a vendor has applied a backport or patch.

The CVSS score of 7.8 classifies this as a high‑severity vulnerability. EPSS is not available, and the advisory does not list it in the CISA KEV catalog, suggesting limited public exploitation evidence to date. However, because the attack requires local access, any user with file system write permissions or any service running as root could potentially exploit the flaw. The likely attack vector is a local attacker gaining write access to the kernel page cache through privileged operations or kernel module loading.