Bug 2481989 (CVE-2026-46086) - CVE-2026-46086 kernel: net: bridge: use a stable FDB dst snapshot in RCU readers
Summary: CVE-2026-46086 kernel: net: bridge: use a stable FDB dst snapshot in RCU readers
Keywords:
Status: NEW
Alias: CVE-2026-46086
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Product Security
QA Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2026-05-27 15:05 UTC by OSIDB Bzimport
Modified: 2026-11-03 09:03 UTC (History)
2 users (show)

Fixed In Version:
Clone Of:
Environment:
Last Closed:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2026:38491 0 None None None 2026-07-13 12:16:10 UTC
Red Hat Product Errata RHSA-2026:39179 0 None None None 2026-07-14 11:46:35 UTC
Red Hat Product Errata RHSA-2026:39180 0 None None None 2026-07-14 11:20:07 UTC
Red Hat Product Errata RHSA-2026:47017 0 None None None 2026-07-28 06:29:36 UTC
Red Hat Product Errata RHSA-2026:91493 0 None None None 2026-10-28 00:48:46 UTC
Red Hat Product Errata RHSA-2026:92997 0 None None None 2026-10-30 07:34:46 UTC
Red Hat Product Errata RHSA-2026:94109 0 None None None 2026-11-02 23:13:01 UTC
Red Hat Product Errata RHSA-2026:94438 0 None None None 2026-11-03 09:03:23 UTC

Description OSIDB Bzimport 2026-05-27 15:05:52 UTC 
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.
Comment 1 Keith Grant 2026-05-27 17:13:35 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026052701-CVE-2026-46086-d3c8@gregkh/T
Comment 5 errata-xmlrpc 2026-07-13 12:16:09 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9

Via RHSA-2026:38491 https://access.redhat.com/errata/RHSA-2026:38491
Comment 6 errata-xmlrpc 2026-07-14 11:20:06 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2026:39180 https://access.redhat.com/errata/RHSA-2026:39180
Comment 7 errata-xmlrpc 2026-07-14 11:46:34 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2026:39179 https://access.redhat.com/errata/RHSA-2026:39179
Comment 9 errata-xmlrpc 2026-07-28 06:29:35 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 10

Via RHSA-2026:47017 https://access.redhat.com/errata/RHSA-2026:47017
Comment 11 Jon Orris 2026-10-28 00:48:45 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support
  Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On

Via RHSA-2026:91493 https://access.redhat.com/errata/RHSA-2026:91493
Comment 12 Jon Orris 2026-10-30 07:34:45 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions
  Red Hat Enterprise Linux 8.8 Telecommunications Update Service

Via RHSA-2026:92997 https://access.redhat.com/errata/RHSA-2026:92997
Comment 13 Jon Orris 2026-11-02 23:13:00 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions

Via RHSA-2026:94109 https://access.redhat.com/errata/RHSA-2026:94109
Comment 15 Jon Orris 2026-11-03 09:03:22 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9.6 Extended Update Support

Via RHSA-2026:94438 https://access.redhat.com/errata/RHSA-2026:94438
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