CVE-2025-21864 tcp: drop secpath at the same time as we currently drop dst
A null pointer dereference in the Linux kernel TCP stack can cause a system crash when network namespaces are deleted while IPsec is active.
- 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-2025-21864?
CVE-2025-21864 is a high-severity vulnerability in Linux kernel, published on 12 Mar 2025. 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:
tcp: drop secpath at the same time as we currently drop dst
Xiumei reported hitting the WARN in xfrm6_tunnel_net_exit while running tests that boil down to: - create a pair of netns - run a basic TCP test over ipcomp6 - delete the pair of netns
The xfrm_state found on spi_byaddr was not deleted at the time we delete the netns, because we still have a reference on it. This lingering reference comes from a secpath (which holds a ref on the xfrm_state), which is still attached to an skb. This skb is not leaked, it ends up on sk_receive_queue and then gets defer-free'd by skb_attempt_defer_free.
The problem happens when we defer freeing an skb (push it on one CPU's defer_list), and don't flush that list before the netns is deleted. In that case, we still have a reference on the xfrm_state that we don't expect at this point.
We already drop the skb's dst in the TCP receive path when it's no longer needed, so let's also drop the secpath. At this point, tcp_filter has already called into the LSM hooks that may require the secpath, so it should not be needed anymore. However, in some of those places, the MPTCP extension has just been attached to the skb, so we cannot simply drop all extensions.
Weakness: CWE-476
Which versions are affected by CVE-2025-21864?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-21864?
Apply the vendor's patch.
Is CVE-2025-21864 being exploited?
There is no known exploitation of CVE-2025-21864 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-58524, BELL-CVE-2025-21864, DEBIAN-CVE-2025-21864, GHSA-qpwf-m697-v547, ROOT-OS-UBUNTU-2404-CVE-2025-21864, UBUNTU-CVE-2025-21864.