CVE-2026-46086

Analyzed Analyzed - Analysis Complete

Use-after-free in Linux Kernel Bridge FDB

Publication date: 2026-05-27

Last updated on: 2026-06-24

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: net: bridge: use a stable FDB dst snapshot in RCU readers Local FDB entries can be rewritten in place by `fdb_delete_local()`, which updates `f->dst` to another port or to `NULL` while keeping the entry alive. Several bridge RCU readers inspect `f->dst`, including `br_fdb_fillbuf()` through the `brforward_read()` sysfs path. These readers currently load `f->dst` multiple times and can therefore observe inconsistent values across the check and later dereference. In `br_fdb_fillbuf()`, this means a concurrent local-FDB update can change `f->dst` after the NULL check and before the `port_no` dereference, leading to a NULL-ptr-deref. Fix this by taking a single `READ_ONCE()` snapshot of `f->dst` in each affected RCU reader and using that snapshot for the rest of the access sequence. Also publish the in-place `f->dst` updates in `fdb_delete_local()` with `WRITE_ONCE()` so the readers and writer use matching access patterns.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-05-27

Last Modified

2026-06-24

Generated

2026-07-07

AI Q&A

2026-05-27

EPSS Evaluated

2026-07-05

NVD

CVE-2026-46086

EUVD

EUVD-2026-32469

Affected Vendors & Products

Vendor	Product	Version / Range
linux	linux_kernel	3.14
linux	linux_kernel	3.14
linux	linux_kernel	3.14
linux	linux_kernel	3.14
linux	linux_kernel	3.14
linux	linux_kernel	3.14
linux	linux_kernel	3.14
linux	linux_kernel	From 6.7 (inc) to 6.12.86 (exc)
linux	linux_kernel	From 6.2 (inc) to 6.6.140 (exc)
linux	linux_kernel	From 6.13 (inc) to 6.18.27 (exc)
linux	linux_kernel	From 6.19 (inc) to 7.0.4 (exc)
linux	linux_kernel	From 5.16 (inc) to 6.1.176 (exc)
linux	linux_kernel	From 5.11 (inc) to 5.15.210 (exc)
linux	linux_kernel	From 3.14.1 (inc) to 5.10.259 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-476	The product dereferences a pointer that it expects to be valid but is NULL.

Attack-Flow Graph

Executive Summary

This vulnerability exists in the Linux kernel's network bridge code, specifically in how local Forwarding Database (FDB) entries are handled. Local FDB entries can be updated in place by the function fdb_delete_local(), which changes a pointer (f->dst) to another port or to NULL while keeping the entry alive.

Several bridge RCU readers inspect this pointer (f->dst) multiple times without taking a stable snapshot, which can lead to inconsistent values being observed during concurrent updates. In particular, the function br_fdb_fillbuf() can see f->dst change after a NULL check but before dereferencing, causing a NULL pointer dereference.

The fix involves taking a single stable snapshot of f->dst using READ_ONCE() in each affected reader and using WRITE_ONCE() in the updater to ensure consistent access patterns, preventing the inconsistent observations and the resulting NULL pointer dereference.

Impact Analysis

This vulnerability can cause a NULL pointer dereference in the Linux kernel's network bridge code, which may lead to a kernel crash or denial of service (DoS) condition.

Since the issue arises from concurrent access to local FDB entries, an attacker with local access might be able to trigger this condition, potentially disrupting network functionality on the affected system.

Mitigation Strategies

The vulnerability has been resolved by updating the Linux kernel to fix the handling of local FDB entries in bridge RCU readers. To mitigate this vulnerability, you should update your Linux kernel to a version that includes the fix for this issue.

Apply the kernel patch that uses READ_ONCE() and WRITE_ONCE() for stable access to f->dst in bridge RCU readers.
Restart the system after updating the kernel to ensure the fix is active.

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