2026-05-15 · view entry permalink →
CVE-2026-46300, Linux kernel: local privilege escalation via xfrm ESP-in-TCP ("Fragnesia"), PoC public
CVE-2026-46300 (codename "Fragnesia") is a local privilege escalation vulnerability in the Linux kernel's xfrm IPsec subsystem, specifically in the ESP-over-TCP code path that provides NAT traversal fallback for IPsec connections (Wiz Research, 2026-05-13 · Help Net Security, 2026-05-14). The vulnerability was discovered by William Bowling of Zellic.io using Zellic's AI-agentic source code auditing tool; Wiz Research (whose researcher Hyunwoo Kim had previously discovered the related Dirty Frag vulnerability family) published the technical writeup. A working proof-of-concept demonstrating escalation from an unprivileged local user to root on unpatched kernels has been released (hosted at github.com/v12-security/pocs). Exploitation requires local code execution on the target; there is no known remote exploitation path absent a prior foothold or a co-chained remote vulnerability (e.g., an RCE that drops a low-privilege shell). Fragnesia is therefore primarily relevant as a post-compromise privilege-escalation primitive and as a jailbreak-class risk in shared compute environments: VPS and bare-metal hosting providers, university Linux clusters, multi-tenant cloud workloads running on shared kernels, and container environments where the kernel namespace boundary can be crossed. MITRE ATT&CK: T1068 (Exploitation for Privilege Escalation). No in-the-wild exploitation reported as of 2026-05-15. Affected: Linux kernels shipping the xfrm ESP-in-TCP implementation across the 5.x and 6.x LTS series, consult your distribution's security bulletin for the exact affected package version range. Distributions shipping patches as of 2026-05-15 include upstream Linux and major vendors (Ubuntu, Debian, RHEL, SUSE); apply the available kernel update and reboot. Interim workaround: disable the xfrm_espintcp kernel module where IPsec ESP-over-TCP is not operationally required (modprobe -r esp6_offload esp4_offload where applicable); also consider restricting CAP_NET_ADMIN capability to reduce the xfrm attack surface in multi-tenant environments.
CVE Summary Table
| CVE | Product | CVSS | EPSS | KEV | Exploited | Patch | Source |
|---|---|---|---|---|---|---|---|
| CVE-2026-20182 | Cisco Catalyst SD-WAN Controller / Manager | 10.0 (v3.1) | n/a | Yes (2026-05-14) | Yes, UAT-8616 + 10+ clusters | 20.9.9.1 / 20.12.7.1 / 20.15.5.2 | Cisco PSIRT |
| CVE-2026-42945 | NGINX Open Source 0.6.27–1.30.0; NGINX Plus R32–R36; NGINX Ingress Controller, Gateway Fabric, F5 WAF/App Protect | 9.2 (v4.0) / 8.1 (v3.1) | n/a | No | No (PoC public) | NGINX OS 1.30.1 / Plus R36 P4 | depthfirst / NCSC-CH |
| CVE-2026-46300 | Linux kernel xfrm ESP-in-TCP subsystem ("Fragnesia"), LPE, local only | 7.8 (v3.1) | n/a | No | No confirmed ITW (Kubernetes PoC public) | Distro kernel updates (2026-05-13+) | Wiz Research |
| CVE-2026-45793 | PHP Composer (1.x, 2.x), GitHub Actions token disclosure in error output | n/a | n/a | No | No | Composer 2.9.8 / 2.2.28 / 1.10.28 | Packagist blog |
net: skbuff: preserve shared-frag marker during coalescing
Three vulnerabilities, collectively known as "Dirty Frag", have been identified in networking subsystems of the Linux kernel, two of which affect Red Hat products.
Red Hat says CVE-2026-43500 doesn't affect its products, while CVE-2026-43284 and CVE-2026-46300 do affect supported Red Hat Enterprise Linux kernels and anything built on them.
Researchers have already published working proof-of-concept exploits for Kubernetes, and Ubuntu spells out the risk of a container escape.
CVE-2026-46300 now carries a published score, CVSS 7.8 (MITRE CVE Program, 2026-09-01), and Red Hat's own security bulletin groups it under the collective "Dirty Frag" name alongside CVE-2026-43284 and CVE-2026-43500, labelling it specifically "Fragnesia (skb coalescing via ESP-in-TCP)": "three vulnerabilities, collectively known as 'Dirty Frag', have been identified in networking subsystems of the Linux kernel, two of which affect Red Hat products" (Red Hat RHSB-2026-003). Applicability splits per CVE: "Red Hat says CVE-2026-43500 doesn't affect its products, while CVE-2026-43284 and CVE-2026-46300 do affect supported Red Hat Enterprise Linux kernels and anything built on them" (Aikido Security, 2026-09-04), any RHEL, OpenShift or RHEL CoreOS estate must confirm the CVE-2026-46300 fix specifically, not only the earlier two. Exploitation now extends to a container-relevant proof-of-concept: "researchers have already published working proof-of-concept exploits for Kubernetes, and Ubuntu spells out the risk of a container escape" (Aikido Security, 2026-09-04), because containers share the host kernel, a compromised workload that can reach the vulnerable code path (governed by seccomp, pod security policy and user-namespace settings) can escalate to root on the node. No source states confirmed in-the-wild exploitation of this specific CVE; Microsoft's previously reported limited in-the-wild activity ("privilege escalation involving 'su'") was itself stated as ambiguous between the "Dirty Frag" family and the separate, earlier "Copy Fail" vulnerability (CVE-2026-31431) from process logs alone (Microsoft Security Blog, 2026-05-08), not a distinction between the two Dirty Frag CVEs themselves, and not specific evidence of exploitation for CVE-2026-46300.