---
id: "CVE-2026-99211"
kind: "vulnerability"
aliases: ["CVE-2026-99211"]
title: "Linux kernel: netlink socket filters can read uninitialized skb headroom"
severity: "low"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["linux-kernel", "netlink", "rdma", "runtime"]
not_affected_if: []
published_at: "2026-10-28T11:17:42+00:00"
first_seen_at: "2026-10-28T11:32:37+00:00"
updated_at: "2026-10-28T11:33:49+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99211", "first_seen_at": "2026-10-28T11:32:37+00:00"}]
---

# Linux kernel: netlink socket filters can read uninitialized skb headroom

In the Linux kernel, netlink messages can be delivered with their socket filter reading from reserved headroom before the message data. An unprivileged NETLINK_RDMA user attaching a classic socket filter can infer this headroom from the length of a delivered reply.

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

## Timeline

- 2026-10-28T11:32:37+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99211

## From the sources

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

netlink: reset skb headers before unicast and multicast filtering

Socket filters can use SKF_NET_OFF and SKF_LL_OFF to read relative to
an skb's network and MAC headers. Netlink producers may reserve
headroom without resetting those headers, allowing a receiving socket's
filter to read data before the initialized message.

For example, IWPM HELLO replies are allocated with dev_alloc_skb(),
which reserves NET_SKB_PAD bytes. An unprivileged NETLINK_RDMA user can
attach a classic socket filter and disclose this headroom through the
length of the delivered reply. The resets in netlink_dump() do not help
because IWPM sends a separately allocated skb through netlink_unicast().

Reset both headers before running the receiver's filter in unicast and
broadcast delivery, as is already done for dump skbs. This also covers
other netlink producers that reserve headroom without changing their
allocation or message-building code.

---

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