---
id: "CVE-2026-99201"
kind: "vulnerability"
aliases: ["CVE-2026-99201"]
title: "Linux kernel: netlink hash leaks network namespace address to unprivileged readers"
severity: "low"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["linux-kernel", "multi-user-hosts", "runtime", "self-hosted"]
not_affected_if: ["patched-kernel"]
published_at: "2026-10-28T11:17:41+00:00"
first_seen_at: "2026-10-28T11:32:37+00:00"
updated_at: "2026-10-28T11:34:01+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99201", "first_seen_at": "2026-10-28T11:32:37+00:00"}]
---

# Linux kernel: netlink hash leaks network namespace address to unprivileged readers

The netlink hash table used a raw kernel pointer to the network namespace, so unprivileged local users could infer bucket order via /proc/net/netlink and socket diagnostics and recover the address of init_net. The fix keys the table on the namespace's non-address net_cookie instead.

_Summary, check and fix written by a model from the sources; labelled as such._

## Fix

- Update the Linux kernel to a release that includes the upstream netlink commit for CVE-2026-99201 (the sources do not list fixed kernel versions)
- Backports are noted for v5.15 and later stable kernels

## Timeline

- 2026-10-28T11:32:37+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99201

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

netlink: avoid hashing the network namespace pointer

The netlink rhashtable key includes a raw struct net pointer and a
user-controlled port ID. Both /proc/net/netlink and socket diagnostics
expose the table's bucket order. By binding and rebinding chosen
NETLINK_USERSOCK port IDs, an unprivileged reader can distinguish equal
buckets and recover the low bits of the Jenkins hash. Its 32-bit seed
and the limited set of kernel-image slides can then be searched offline
to recover the address of init_net.

Use the namespace's unique, non-address net_cookie in the comparison
key instead. It is assigned before the per-net initializers run and
remains unchanged for the namespace's lifetime. The lookup key and
object hash are still built by netlink_compare_arg_init(), keeping
lookup, insertion, removal and rehashing consistent while preserving
namespace separation. Neither public table walker needs to change.

Reading the socket's namespace cookie in netlink_compare() is safe
under RCU, including during namespace teardown. netlink_release()
removes the socket from the hash table and defers its final put with
call_rcu(). cleanup_net() runs the per-net exit methods and waits for
outstanding RCU callbacks with rcu_barrier() before freeing namespace
storage.

Unlike ns.ns_id, net_cookie is also available and initialized during
setup_net() in older stable kernels, making the change straightforward
to backport to v5.15 and later.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_