# CVE-2021-47106: netfilter: nf_tables: fix use-after-free in nft_set_catchall_destroy()

> A use-after-free vulnerability in the Linux kernel's netfilter subsystem allows local attackers to potentially execute arbitrary code or escalate privileges.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Mar 2024
- **Updated:** 5 Aug 2026
- **Also known as:** DEBIAN-CVE-2021-47106, GHSA-gmwj-428v-53wv, UBUNTU-CVE-2021-47106

## What is CVE-2021-47106?

CVE-2021-47106 is a high-severity use after free vulnerability in Linux kernel, published on 4 Mar 2024. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

netfilter: nf_tables: fix use-after-free in nft_set_catchall_destroy()

We need to use list_for_each_entry_safe() iterator
because we can not access @catchall after kfree_rcu() call.

syzbot reported:

BUG: KASAN: use-after-free in nft_set_catchall_destroy net/netfilter/nf_tables_api.c:4486 [inline]
BUG: KASAN: use-after-free in nft_set_destroy net/netfilter/nf_tables_api.c:4504 [inline]
BUG: KASAN: use-after-free in nft_set_destroy+0x3fd/0x4f0 net/netfilter/nf_tables_api.c:4493
Read of size 8 at addr ffff8880716e5b80 by task syz-executor.3/8871

CPU: 1 PID: 8871 Comm: syz-executor.3 Not tainted 5.16.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_address_description.constprop.0.cold+0x8d/0x2ed mm/kasan/report.c:247
 __kasan_report mm/kasan/report.c:433 [inline]
 kasan_report.cold+0x83/0xdf mm/kasan/report.c:450
 nft_set_catchall_destroy net/netfilter/nf_tables_api.c:4486 [inline]
 nft_set_destroy net/netfilter/nf_tables_api.c:4504 [inline]
 nft_set_destroy+0x3fd/0x4f0 net/netfilter/nf_tables_api.c:4493
 __nft_release_table+0x79f/0xcd0 net/netfilter/nf_tables_api.c:9626
 nft_rcv_nl_event+0x4f8/0x670 net/netfilter/nf_tables_api.c:9688
 notifier_call_chain+0xb5/0x200 kernel/notifier.c:83
 blocking_notifier_call_chain kernel/notifier.c:318 [inline]
 blocking_notifier_call_chain+0x67/0x90 kernel/notifier.c:306
 netlink_release+0xcb6/0x1dd0 net/netlink/af_netlink.c:788
 __sock_release+0xcd/0x280 net/socket.c:649
 sock_close+0x18/0x20 net/socket.c:1314
 __fput+0x286/0x9f0 fs/file_table.c:280
 task_work_run+0xdd/0x1a0 kernel/task_work.c:164
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:175 [inline]
 exit_to_user_mode_prepare+0x27e/0x290 kernel/entry/common.c:207
 __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
 syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:300
 do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f75fbf28adb
Code: 0f 05 48 3d 00 f0 ff ff 77 45 c3 0f 1f 40 00 48 83 ec 18 89 7c 24 0c e8 63 fc ff ff 8b 7c 24 0c 41 89 c0 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 44 89 c7 89 44 24 0c e8 a1 fc ff ff 8b 44
RSP: 002b:00007ffd8da7ec10 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 00007f75fbf28adb
RDX: 00007f75fc08e828 RSI: ffffffffffffffff RDI: 0000000000000003
RBP: 00007f75fc08a960 R08: 0000000000000000 R09: 00007f75fc08e830
R10: 00007ffd8da7ed10 R11: 0000000000000293 R12: 00000000002067c3
R13: 00007ffd8da7ed10 R14: 00007f75fc088f60 R15: 0000000000000032
 </TASK>

Allocated by task 8886:
 kasan_save_stack+0x1e/0x50 mm/kasan/common.c:38
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc mm/kasan/common.c:513 [inline]
 ____kasan_kmalloc mm/kasan/common.c:472 [inline]
 __kasan_kmalloc+0xa6/0xd0 mm/kasan/common.c:522
 kasan_kmalloc include/linux/kasan.h:269 [inline]
 kmem_cache_alloc_trace+0x1ea/0x4a0 mm/slab.c:3575
 kmalloc include/linux/slab.h:590 [inline]
 nft_setelem_catchall_insert net/netfilter/nf_tables_api.c:5544 [inline]
 nft_setelem_insert net/netfilter/nf_tables_api.c:5562 [inline]
 nft_add_set_elem+0x232e/0x2f40 net/netfilter/nf_tables_api.c:5936
 nf_tables_newsetelem+0x6ff/0xbb0 net/netfilter/nf_tables_api.c:6032
 nfnetlink_rcv_batch+0x1710/0x25f0 net/netfilter/nfnetlink.c:513
 nfnetlink_rcv_skb_batch net/netfilter/nfnetlink.c:634 [inline]
 nfnetlink_rcv+0x3af/0x420 net/netfilter/nfnetlink.c:652
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x904/0xdf0 net/netlink/af_netlink.c:1921
 sock_sendmsg_nosec net/
---truncated---

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-47106?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47106?

Apply the vendor's patch.

## Is CVE-2021-47106 being exploited?

There is no known exploitation of CVE-2021-47106 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-47106 and fix it if it is affected.

What it is: CVE-2021-47106 is a high-severity use after free vulnerability in Linux kernel, published on 4 Mar 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-47106 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-47106/ (Markdown: https://insights.sbomify.com/CVE-2021-47106/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47106
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47106
- OSV: https://osv.dev/vulnerability/CVE-2021-47106

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47106/
Summaries are generated and may contain mistakes; the official description above is the record.