CVE-2021-47452 netfilter: nf_tables: skip netdev events generated on netns removal
A race condition in Linux kernel netfilter handling during network namespace removal can trigger a kernel warning, potentially leading to system instability or denial of service.
- 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
What is CVE-2021-47452?
CVE-2021-47452 is a medium-severity denial of service vulnerability in Linux kernel, published on 22 May 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: 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.
Which versions are affected by CVE-2021-47452?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2021-47452?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2021-47452 being exploited?
There is no known exploitation of CVE-2021-47452 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2021-47452, GHSA-hxw5-pvw5-67pp, ROOT-OS-DEBIAN-11-CVE-2021-47452, UBUNTU-CVE-2021-47452.