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Linux KernelOperating system · Linux

CVE-2021-47408

MEDIUM · 5.5 CVSS v3.1 Published 2024-05-21
Fix available
A fix is available. Upgrade to 5.10.71 / 5.14.10 or later.
See remediation →
57/100
Remediation priority · Elevated
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: serialize hash resizes and cleanups Syzbot was able to trigger the following warning [1] No repro found by syzbot yet but I was able to trigger similar issue by having 2 scripts running in parallel, changing conntrack hash sizes, and: for j in `seq 1 1000` ; do unshare -n /bin/true >/dev/null ; done It would take more than 5 minutes for net_namespace structures to be cleaned up. This is because nf_ct_iterate_cleanup() has to restart everytime a resize happened. By adding a mutex, we can serialize hash resizes and cleanups and also make get_next_corpse() faster by skipping over empty buckets. Even without resizes in the picture, this patch considerably speeds up network namespace dismantles. [1] INFO: task syz-executor.0:8312 can't die for more than 144 seconds. task:syz-executor.0 state:R running task stack:25672 pid: 8312 ppid: 6573 flags:0x00004006 Call Trace: context_switch kernel/sched/core.c:4955 [inline] __schedule+0x940/0x26f0 kernel/sched/core.c:6236 preempt_schedule_common+0x45/0xc0 kernel/sched/core.c:6408 preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:35 __local_bh_enable_ip+0x109/0x120 kernel/softirq.c:390 local_bh_enable include/linux/bottom_half.h:32 [inline] get_next_corpse net/netfilter/nf_conntrack_core.c:2252 [inline] nf_ct_iterate_cleanup+0x15a/0x450 net/netfilter/nf_conntrack_core.c:2275 nf_conntrack_cleanup_net_list+0x14c/0x4f0 net/netfilter/nf_conntrack_core.c:2469 ops_exit_list+0x10d/0x160 net/core/net_namespace.c:171 setup_net+0x639/0xa30 net/core/net_namespace.c:349 copy_net_ns+0x319/0x760 net/core/net_namespace.c:470 create_new_namespaces+0x3f6/0xb20 kernel/nsproxy.c:110 unshare_nsproxy_namespaces+0xc1/0x1f0 kernel/nsproxy.c:226 ksys_unshare+0x445/0x920 kernel/fork.c:3128 __do_sys_unshare kernel/fork.c:3202 [inline] __se_sys_unshare kernel/fork.c:3200 [inline] __x64_sys_unshare+0x2d/0x40 kernel/fork.c:3200 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7f63da68e739 RSP: 002b:00007f63d7c05188 EFLAGS: 00000246 ORIG_RAX: 0000000000000110 RAX: ffffffffffffffda RBX: 00007f63da792f80 RCX: 00007f63da68e739 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000040000000 RBP: 00007f63da6e8cc4 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f63da792f80 R13: 00007fff50b75d3f R14: 00007f63d7c05300 R15: 0000000000022000 Showing all locks held in the system: 1 lock held by khungtaskd/27: #0: ffffffff8b980020 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6446 2 locks held by kworker/u4:2/153: #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: arch_atomic_long_set include/linux/atomic/atomic-long.h:41 [inline] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: atomic_long_set include/linux/atomic/atomic-instrumented.h:1198 [inline] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:634 [inline] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:661 [inline] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x896/0x1690 kernel/workqueue.c:2268 #1: ffffc9000140fdb0 ((kfence_timer).work){+.+.}-{0:0}, at: process_one_work+0x8ca/0x1690 kernel/workqueue.c:2272 1 lock held by systemd-udevd/2970: 1 lock held by in:imklog/6258: #0: ffff88807f970ff0 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:990 3 locks held by kworker/1:6/8158: 1 lock held by syz-executor.0/8312: 2 locks held by kworker/u4:13/9320: 1 lock held by ---truncated---

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis

A detailed technical summary for this CVE is being prepared.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:< 5.10.71>= 5.11, < 5.14.10= 5.15

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.10.71 / 5.14.10 or later
Fixed in 5.10.715.14.10
Vendor patch git.kernel.org →
Recommended fix High confidence

Linux kernel >= 5.10.71, >= 5.14.10, or > 5.15 (e.g., 5.15.1 or later)

  1. Identify the current running kernel version using `uname -r`
  2. If running a version < 5.10.71, upgrade to kernel 5.10.71 or later
  3. If running version 5.11.x through 5.14.9, upgrade to kernel 5.14.10 or later
  4. If running version 5.15.0, upgrade to kernel 5.15.1 or later
  5. Apply the upgrade via the distribution's package manager (e.g., `apt-get update && apt-get upgrade`, `yum update`, or `dnf upgrade`)
  6. Reboot the system to load the fixed kernel
  7. Verify the kernel version after reboot using `uname -r` to confirm the fix is applied
Caveat Kernel upgrades may require rebooting services and could have driver compatibility considerations; test in a staging environment before deploying to production

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-47408 in production — separate from our analysis above.

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