Linux distros are rolling out patches for a new high-severity kernel privilege escalation vulnerability that allows attackers to run malicious code as root.

Known as Fragnasia and tracked as CVE-2026–46300, this security flaw stems from a logic bug in the Linux XFRM ESP-in-TCP subsystem that can enable unprivileged local attackers to gain root privileges by writing arbitrary bytes to the kernel page cache of read-only files.

Zellic’s head of assurance, William Bowling, who discovered this new universal local privilege escalation flaw, also shared a proof-of-concept (PoC) exploit that achieves a memory-write primitive in the kernel that is used to corrupt the page cache memory of the /usr/bin/su binary to get a shell with root privileges on vulnerable systems.