Fragnesia (CVE-2026-46300): Frequently asked questions about new Linux Kernel XFRM ESP-in-TCP privilege escalation

5-minute read May 14 2026 Fragnesia (CVE-2026-46300): Frequently asked questions about new Linux Kernel XFRM ESP-in-TCP privilege escalation By Satnam Narang Subscribe A new Linux kernel local privilege escalation exploit with a public proof-of-concept targets the same subsystem as Dirty Frag but requires a separate patch. Key Takeaways CVE-2026-46300 (Fragnesia) is the latest high severity local privilege escalation vulnerability in the Linux kernel, following the disclosure of both Dirty Frag and Copy Fail. A public proof-of-concept is available and the exploit has been confirmed working on Ubuntu systems, though no in-the-wild exploitation has been reported. A kernel patch was released on May 13; the existing Dirty Frag patches do not address this flaw, though the module blacklist mitigation protects against both. Background Tenable's Research Special Operations (RSO) team has compiled this blog to answer Frequently Asked Questions (FAQ) regarding Fragnesia, a new Linux kernel local privilege escalation vulnerability. FAQ When was Fragnesia first disclosed? On May 13, William Bowling of V12 Security publicly disclosed Fragnesia alongside a proof-of-concept exploit and a corresponding kernel patch. CVE-2026-46300 was assigned the same day. What is Fragnesia? Fragnesia is a local privilege escalation vulnerability in the Linux kernel's XFRM ESP-in-TCP subsystem. The name references how the socket buffer (skb) "forgets" that a frag is shared during coalescing. Specifically, when the kernel coalesces socket buffer fragments via skb_try_coalesce(), it fails to propagate the SKBFL_SHARED_FRAG flag that marks certain pages as shared with other subsystems. Without that flag, the kernel treats those file-cache-backed pages as safe to write. CVE Description CVSSv3 CVE-2026-46300 Linux Kernel XFRM ESP-in-TCP Local Privilege Escalation Vulnerability 7.8 (estimated) How does Fragnesia relate to Dirty Frag? Fragnesia belongs to the same vulnerability class as Dirty Frag (CVE-2026-43284/CVE-2026-43500) in that both achieve page-cache writes through the XFRM/ESP subsystem. However, they are distinct vulnerabilities: Dirty Frag Fragnesia Researcher Hyunwoo Kim William Bowling (V12 Security) Entry point xfrm-ESP page-cache write TCP coalescing in ESP-in-TCP (ULP mode transition) Write primitive 4-byte STORE 192-byte XOR via AES-GCM keystream Patch Existing Dirty Frag patches New patch (May 13) The existing kernel patches for Dirty Frag do not fix Fragnesia. A separate patch is required. How severe is Fragnesia? Any local user on a system running a vulnerable kernel can exploit Fragnesia to gain root access. The exploit does not rely on a race condition. The technique uses user and network namespaces (enabled by default on most distributions) to obtain CAP_NET_ADMIN without requiring elevated host privileges. The public PoC targets /usr/bin/su, modifying it in the page cache to grant root on execution. The on-disk binary is never changed, and a reboot or cache flush restores normal behavior. The technique is not limited to a single binary: any file readable by the attacker is a viable target, including [redacted]. Which Linux distributions are affected? Fragnesia affects the same kernel versions as Dirty Frag. Any distribution shipping a kernel without the May 13 patch is vulnerable. The vulnerability was confirmed working on Ubuntu 6.8.0-111-generic (April 11, 2026 build) running on a Linode VPS. Affected distributions include: Distribution Patch Status Ubuntu Vulnerable Red Hat Enterprise Linux Vulnerable openSUSE Vulnerable CentOS Stream Vulnerable AlmaLinux Patched CloudLinux Patching Debian Vulnerable Gentoo Vulnerable Fedora Patched Amazon Linux Not affected Amazon Linux is not affected as it does not ship the espintcp module. CloudLinux 7 is also unaffected. As of May 14, Ubuntu's patch status remains "needs evaluation" across all releases. CloudLinux has patches in testing for CL9/CL10 and a KernelCare livepatch in validation. Is there a proof-of-concept (PoC) available? Yes. A public PoC was released on GitHub alongside the disclosure. Are patches or mitigations available? A kernel patch was submitted to the netdev mailing list on May 13. The fix ensures skb_try_coalesce() propagates the SKBFL_SHARED_FRAG marker, preventing in-place decryption of shared page-cache fragments. AlmaLinux has released patched kernels for all supported releases: Distribution Fixed Kernel Version AlmaLinux 8 kernel-4.18.0-553.124.2.el8_10 AlmaLinux 9 kernel-5.14.0-611.54.4.el9_7 AlmaLinux 10 kernel-6.12.0-124.56.2.el10_1 For systems where an immediate kernel update is not feasible, the same module blacklist mitigation used for Dirty Frag is effective: rmmod esp4 esp6 rxrpc printf 'install esp4 /bin/false\ninstall esp6 /bin/false\ninstall rxrpc /bin/false\n' > /etc/modprobe.d/dirtyfrag.conf Organizations that applied this mitigation for Dirty Frag are already protected against Fragnesia. Organizations that applied only the kernel patches for Dirty Frag without the module blacklist are not protected and need the new patch. Historical exploitation of Linux kernel vulnerabilities The Linux kernel has been a recurring target for privilege escalation attacks. CISA's Known Exploited Vulnerabilities catalog contains entries for several Linux kernel flaws: CVE Description Date Added to KEV Known Ransomware Use CVE-2016-5195 Linux Kernel Race Condition (Dirty Cow) 2022-03-03 Unknown CVE-2022-0847 Linux Kernel Improper Initialization (Dirty Pipe) 2022-04-25 Unknown CVE-2024-1086 Linux Kernel nf_tables Use-After-Free 2024-05-30 Known CVE-2026-31431 Linux Kernel Incorrect Resource Transfer (Copy Fail) 2026-05-01 Unknown Copy Fail (CVE-2026-31431) was added to the KEV catalog on May 1. CVE-2026-46300 (Fragnesia) is not currently in the KEV catalog. Tenable published an FAQ blog on Dirty Frag and Copy Fail, both of which are Linux kernel privilege escalation vulnerabilities disclosed in 2026. Has Tenable released any product coverage for this vulnerability? A list of Tenable plugins for this vulnerability can be found on the CVE-2026-46300 page as they're released. This link will display all available plugins for this vulnerability, including upcoming plugins in our Plugins Pipeline. Join Tenable's Research Special Operations (RSO) Team on Tenable Connect for further discussions on the latest cyber threats. Learn more about Tenable One, the Exposure Management Platform for the modern attack surface. Author Learn more Satnam Narang SENIOR STAFF RESEARCH ENGINEER, SECURITY RESPONSE Satnam joined Tenable in 2018. He has over 15 years experience in the industry (M86 Security and Symantec). He contributed to the Anti-Phishing Working Group, helped develop a Social Networking Guide for the National Cyber Security Alliance, uncovered a huge spam botnet on Twitter and was the first ... 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