Stale rcu_barrier() stalls RTNL lock in Linux kernel bridge
Key facts
- Attack vector
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- Privileges required
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- User interaction
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- Attack complexity
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- Impact type
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- Confidentiality · integrity · availability
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- Fix status
- Partial Red Hat: 5 without a fix
No CVSS vector from any source. Fix status from CNA and Red Hat.
Summary
The Linux kernel net bridge multicast code is affected. A stale rcu_barrier() call in br_multicast_dev_del() waits for RCU callbacks during bridge device removal, which holds the RTNL lock for long periods. Under heavy network namespace cleanup, this blocks other tasks on the RTNL mutex, as seen in syzbot reports.
Written with Claude Haiku 5.5 from the sources below · 2026-10-28
Description from the CNA
In the Linux kernel, the following vulnerability has been resolved: net: bridge: remove stale rcu_barrier() in br_multicast_dev_del() This rcu_barrier() came from a time call_rcu() calls were used in net/bridge/br_multicast.c. Now kfree_rcu() is there, we can remove this problematic rcu_barrier() which causes extreme RTNL pressure in many syzbot reports. INFO: task syz-executor:77945 is blocked on a mutex likely owned by task kworker/u1024:5:36537. task:kworker/u1024:5 state:D stack:24616 pid:36537 tgid:36537 ppid:2 task_flags:0x4208060 flags:0x00080000 last_sleep:612797637337 Workqueue: netns cleanup_net Call Trace: <TASK> [<ffffffff81914eaa>] context_switch+0xf2a/0x1730 kernel/sched/core.c:6483 [<ffffffff81201143>] __schedule+0x1133/0x43a0 kernel/sched/core.c:8411 [<ffffffff8120446b>] __schedule_loop kernel/sched/core.c:8514 [inline] [<ffffffff8120446b>] schedule+0xab/0x260 kernel/sched/core.c:8529 [<ffffffff8121a093>] schedule_timeout+0xc3/0x2b0 kernel/time/sleep_timeout.c:75 [<ffffffff81205347>] do_wait_for_common kernel/sched/completion.c:100 [inline] [<ffffffff81205347>] __wait_for_common kernel/sched/completion.c:121 [inline] [<ffffffff81205347>] wait_for_common kernel/sched/completion.c:132 [inline] [<ffffffff81205347>] wait_for_completion+0x2c7/0x5d0 kernel/sched/completion.c:153 [<ffffffff81b8f27f>] rcu_barrier+0x49f/0x620 kernel/rcu/tree.c:3888 [<ffffffff860091b3>] br_multicast_dev_del+0x303/0x350 net/bridge/br_multicast.c:4459 [<ffffffff85fb5dbc>] br_dev_uninit+0x1c/0x40 net/bridge/br_device.c:157 [<ffffffff8568058c>] unregister_netdevice_many_notify+0x1c1c/0x2300 net/core/dev.c:12599 [<ffffffff8562be43>] ops_exit_rtnl_list net/core/net_namespace.c:187 [inline] [<ffffffff8562be43>] ops_undo_list+0x3d3/0x940 net/core/net_namespace.c:248
Why it matters now
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
Remediation
Update the Linux kernel to 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111, 6.18.53 or 7.2, or a later release that includes the fixing commits. Red Hat Enterprise Linux 6 has no fix planned, and Red Hat Enterprise Linux 8, 9, 10 and OpenShift Container Platform 4 have no fix available yet.
Written with Claude Haiku 5.5 from the sources below · 2026-10-28
- Fix · CNA Linux (Linux) Fixed in 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111, 6.18.53, 7.2
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 10 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 8 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 9 | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift Container Platform 4 | Affected | No fix yet: Fix deferred |
Not affected: 1 product
- Red Hat Enterprise Linux 7
Timeline
- 2026-10-23 Threatist record created from CVE-2026-98881
- 2026-10-23 Alias added: GHSA-52xp-vqwj-rp88
- 2026-10-26 Fix available: Linux/Linux@0 · CNA
- 2026-10-26 Affected versions changed · Red Hat
- 2026-10-26 CVSS score added · Red Hat
References
Other 7
- https://git.kernel.org/stable/c/35f9f11740515a10b084adfb1ce691351f2452ab
- https://git.kernel.org/stable/c/0443f6aac6bf6a91e406273fdda11497cef6ad07
- https://git.kernel.org/stable/c/ac0e823a228f94ad9d7a3d876cc07e59a7afb806
- https://git.kernel.org/stable/c/f0018acf0b66f93a292667c9a9c2a26c570cf270
- https://git.kernel.org/stable/c/372ee8fbe0f796031c60f676ec90f0788c26523d
- https://git.kernel.org/stable/c/39679927fa7aaf4601119f7234342d1b5d4f6f84
- https://git.kernel.org/stable/c/25ae123db10ba9ab890b56bcdb0a4363aee8529a
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Sources
- CVE-2026-98881 · CVE Program
- CVE-2026-98881 · NVD
- FIRST EPSS
- GHSA-52xp-vqwj-rp88 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-98881 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences