---
id: "CVE-2026-98487"
kind: "vulnerability"
aliases: ["CVE-2026-98487"]
title: "Linux kernel: bridge multicast group deletion leaves a dangling pointer"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["bridge", "kubernetes", "linux-kernel", "networking", "package", "self-hosted"]
not_affected_if: ["multicast-snooping-disabled", "no-linux-bridge"]
published_at: "2026-10-18T16:16:59+00:00"
first_seen_at: "2026-10-23T21:57:15+00:00"
updated_at: "2026-10-25T05:25:46+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98487", "first_seen_at": "2026-10-23T21:57:15+00:00"}]
---

# Linux kernel: bridge multicast group deletion leaves a dangling pointer

A Linux kernel bridge multicast (MDB) bug frees port group entries while a cursor still points at them, so a later netlink MDB dump reads freed memory. The sources do not describe a confirmed attacker-controlled path, so the impact beyond a kernel memory read and crash is unknown.

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

## How to check

- `uname -r` and compare the running kernel against the fixed kernel versions in the upstream stable advisory (unknown from these sources)
- `bridge mdb show` on hosts that use Linux bridges with multicast snooping, to confirm the bridge feature is in use

## Fix

- Update to a Linux kernel release that includes the upstream commit 'net: bridge: mdb: restart port group walk after deletion' (exact fixed version unknown from these sources)
- Reboot after the kernel update so the fixed code is running

## Timeline

- 2026-10-23T21:57:15+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98487

## From the sources

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

net: bridge: mdb: restart port group walk after deletion

br_mdb_flush_pgs() keeps a pointer-to-pointer cursor while walking
mp->ports. br_multicast_del_pg() can re-enter the same MDB entry through
br_multicast_sg_del_exclude_ports() and unlink other port groups. If the
cursor points into one of those groups, the next iteration dereferences a
stale cursor and can leave mp->ports pointing at freed memory.

A following RTM_GETMDB exposes the dangling pointer:

  BUG: KASAN: slab-use-after-free in br_mdb_dump
  Read of size 8
    br_mdb_dump
    rtnl_mdb_dump
    rtnl_dumpit
    netlink_dump

Reset the cursor to mp->ports after every deletion. The deletion removes at
least the selected group, so the restarted walk always makes progress.

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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_