CVE-2026-80521
Summary
A use-after-free in the Linux kernel's AF_UNIX socket garbage collector lets an attacker inside a container escape namespace isolation, cgroup limits and seccomp filtering to gain root on the host. NVD records it at CVSS 3.1 7.8 (High); the severity of the score understates the consequence, because the flaw converts a container boundary — normally the primary isolation control for multi-tenant and CI workloads — into no boundary at all.
Details
The fault is in the kernel's handling of SCM_RIGHTS file-descriptor passing between processes over AF_UNIX sockets. A race condition lets the garbage collector observe new references before the data carrying them has been queued by skb_queue_tail(); if collection runs inside that window it frees part of a group of linked sockets while a pointer to them survives in a persistent internal list, and the next collection pass follows that pointer into freed memory. NVD's record describes the resolution as af_unix: Unlink scc_entry in unix_del_edge(), fixing a case where GC could free a dead strongly-connected component partially.
The reach is the operationally important part: AF_UNIX sockets are permitted by default in Docker and Kubernetes seccomp profiles, so the exploit reaches the kernel through ordinary system calls a container is already entitled to make and bypasses the isolation controls defenders rely on for untrusted workloads.
| Attribute | Detail |
|---|---|
| CVE | CVE-2026-80521 |
| CVSS | 7.8 (NVD, CVSS 3.1) — High |
| Vendor / product | Linux kernel (AF_UNIX); Ubuntu LTS kernels and their AWS, Azure and GCP variants |
| Reported | 22 September 2026 (public exploit); upstream fix 6 August 2026 |
Patch status
The upstream fix landed on 6 August 2026 in mainline kernel 7.2 and stable branch 7.1.10; the vulnerable code was introduced in kernel 6.10 and backported to stable branches 6.1 and 6.6, which widens the affected base considerably. As at 22 September, Ubuntu has not shipped the fix for 26.04, 24.04 or 22.04 LTS — its security tracker lists the package as "vulnerable, work in progress" with no published date — and the AWS, Azure and GCP kernel packages on those releases inherit it. DepthFirst released exploit code targeting Ubuntu 26.04. Neither DepthFirst nor Ubuntu has published a workaround; the advisory guidance is to avoid running untrusted workloads on affected kernels. The flaw is not in CISA's KEV catalog and there are no confirmed reports of exploitation in the wild.
Australian Significance
Ubuntu LTS is the default base image and host distribution across a large share of Australian enterprise, government and cloud workloads, and the affected kernel packages include the AWS, Azure and GCP variants Australian organisations run in the major clouds. Any environment scheduling untrusted or third-party containers — CI runners, multi-tenant hosting, sandboxed analysis — should assume the container boundary is currently absent on affected kernels, since neither namespace isolation nor seccomp blocks this path.