Linux admins hoping Dirty Frag was a one-off horror from the kernel networking stack are about to have a considerably worse week. Researchers at Wiz have published an analysis of "Fragnesia," a Linux kernel local privilege escalation flaw discovered by William Bowling of the V12 security team that allows unprivileged users to gain root by corrupting page cache memory. The bug, tracked as CVE-2026-46300, has public proof-of-concept exploit code documented by V12 on GitHub that demonstrates the vulnerability being used against /usr/bin/su to spawn a root shell. According to Google-owned Wiz, the flaw sits in the Linux kernel's XFRM subsystem, specifically ESP-in-TCP processing tied to IPsec support. By carefully triggering the bug, attackers can modify protected file data in memory without changing the original files stored on disk. Wiz describes Fragnesia as part of the broader "Dirty Frag" bug family rather than a completely separate class of issue. Dirty Frag itself only surfaced days ago and was already attracting attention thanks to public exploit code, incomplete patch coverage, and unusually reliable privilege escalation. According to researcher Hyunwoo Kim, who uncovered Dirty Frag, "Fragnesia" emerged as an unintended side effect of patches shipped to fix the original Dirty Frag vulnerabilities, adding yet another entry to the long tradition of security fixes accidentally creating new security problems. As The Register previously reported, Dirty Frag followed hot on the heels of Copy Fail, another Linux kernel privilege escalation flaw that abused page cache handling to overwrite supposedly read-only files. Historically, local Linux privilege escalation bugs had a reputation for being unreliable, crash-prone, or fiddly enough that attackers needed good timing and a fair bit of luck to pull them off cleanly. Fragnesia looks different, as Wiz and V12 both say the exploit avoids race conditions entirely, making it far more predictable than older Linux root exploits like Dirty COW. That makes the bug much more useful after an initial compromise. An attacker who gains access to a system through phishing, stolen credentials, or a vulnerable cloud workload suddenly has a cleaner path to full root access. The V12 proof-of-concept repository is already public, while Linux vendors have started pushing out advisories and mitigation guidance. AlmaLinux warned that all supported releases are affected and urged administrators to patch quickly or disable unused ESP-related functionality where possible. Similar advisories have also been issued by Amazon Linux, CloudLinux, Debian, Gentoo, Red Hat Enterprise Linux, SUSE, and Ubuntu as distributors scramble to assess exposure across supported kernel versions. Microsoft also urged organizations to patch quickly, noting that though it had not observed in-the-wild exploitation so far, Fragnesia "can modify any file readable by the user, including [/]etc[/]passwd." The Linux networking stack is starting to look less like infrastructure and more like a root exploit vending machine. ®
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