New Fragnesia Linux Kernel LPE Grants Root Access via Page Cache Corruption
A new Linux kernel local privilege escalation vulnerability tracked as CVE-2026-46300 and named Fragnesia allows unprivileged attackers to corrupt the page cache of read-only files to gain root access without requiring a race condition.
A new Linux kernel local privilege escalation vulnerability, tracked as CVE-2026-46300 (CVSS 7.8) and codenamed Fragnesia, has been disclosed. The bug resides in the XFRM ESP-in-TCP subsystem and allows unprivileged local attackers to corrupt the kernel page cache of read-only files, such as /usr/bin/su, to gain root access without requiring a race condition. A proof-of-concept exploit has been released, and patches are available from major Linux distributions including Red Hat, Debian, Ubuntu, and SUSE. No in-the-wild exploitation has been observed yet, but administrators are urged to apply mitigations similar to those for the related Dirty Frag vulnerability.
Fragnesia was discovered by researcher William Bowling of Zellic and the V12 security team. According to Google-owned Wiz, the vulnerability allows unprivileged local attackers to modify read-only file contents in the kernel page cache and achieve root privileges through a deterministic page-cache corruption primitive. This is the third such bug identified in the kernel within two weeks, following Copy Fail and Dirty Frag (aka Copy Fail 2).
The vulnerability is rooted in a logic bug in the Linux XFRM ESP-in-TCP subsystem. V12 explained V12. It achieves arbitrary byte writes into the kernel page cache of read-only files without requiring any race condition. This makes exploitation deterministic and reliable across major distributions. A proof-of-concept exploit has been released by V12.
Multiple Linux distributions have released advisories including AlmaLinux, Amazon Linux, CloudLinux, Debian, Gentoo, Red Hat Enterprise Linux, SUSE, and Ubuntu. CloudLinux maintainers noted that customers who have already applied the Dirty Frag mitigation need no further action until patched kernels are released. Red Hat said it is performing an assessment to confirm if existing mitigations extend to CVE-2026-46300.
Microsoft urged users to apply the patch as soon as possible by running update tools. If patching is not possible, administrators should consider applying the same mitigations as for Dirty Frag. This includes disabling esp4, esp6, and related xfrm/IPsec functionality, restricting unnecessary local shell access, hardening containerized workloads, and increasing monitoring for abnormal privilege escalation activity.
Wiz noted that AppArmor restrictions on unprivileged user namespaces may serve as a partial mitigation, requiring additional bypasses for successful exploitation. However, unlike Dirty Frag, no host-level privileges are required for Fragnesia. The development comes as a threat actor named berz0k has been observed advertising on cybercrime forums a zero-day Linux LPE exploit for $170,000, claiming it works on multiple major Linux distributions.
ThreatMon reported in a post on X that the threat actor claims the vulnerability is TOCTOU-based (Time-of-Check Time-of-Use), capable of stable local privilege escalation without causing system crashes, and leverages a shared object (.so) payload dropped into the /tmp directory. This highlights the ongoing interest in Linux kernel vulnerabilities among cybercriminals.