CVE-2025-21864

/// Technical 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 a

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References