# CVE-2021-47452: linux: In the Linux kernel, the following vulnerability has been resolved:  netfilter: nf_tables: skip netdev events generat...

CVE-2021-47452 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47452, released May 22, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47452
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0020
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 22, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  netfilter: nf_tables: skip netdev events generated on netns removal  syzbot reported following (harmless) WARN:   WARNING: CPU: 1 PID: 2648 at net/netfilter/core.c:468   nft_netdev_unregister_hooks net/netfilter/nf_tables_api.c:230 [inline]   nf_tables_unregister_hook include/net/netfilter/nf_tables.h:1090 [inline]   __nft_release_basechain+0x138/0x640 net/netfilter/nf_tables_api.c:9524   nft_netdev_event net/netfilter/nft_chain_filter.c:351 [inline]   nf_tables_netdev_event+0x521/0x8a0 net/netfilter/nft_chain_filter.c:382  reproducer: unshare -n bash -c 'ip link add br0 type bridge; nft add table netdev t ; \  nft add chain netdev t ingress \{ type filter hook ingress device "br0" \  priority 0\; policy drop\; \}'  Problem is that when netns device exit hooks create the UNREGISTER event, the .pre_exit hook for nf_tables core has already removed the base hook.  Notifier attempts to do this again.  The need to do base hook unregister unconditionally was needed in the past, because notifier was last stage where reg->dev dereference was safe.  Now that nf_tables does the hook removal in .pre_exit, this isn't needed anymore.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.14.16-1 | [DEBIAN-CVE-2021-47452](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47452.md) | May 22, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.14.16-1 | [DEBIAN-CVE-2021-47452](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47452.md) | May 22, 2024 |
| Linux | linux Debian 14 | 5.14.16-1 | [DEBIAN-CVE-2021-47452](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47452.md) | May 22, 2024 |

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