CVE-2025-21759

Summary

CVE-2025-21759 is a vulnerability affecting the Linux kernel's ipv6 subsystem. The issue lies in the function igmp6_send(), which can be called without the necessary RTNL or RCU (Read-Copy-Update) locks held. This lack of protection can lead to a use-after-free (UAF) vulnerability. To mitigate the risk, RCU protection has been extended in igmp6_send(), and the function now uses alloc_skb() instead of sock_alloc_send_skb() to allocate send sockets under RCU protection. The change eliminates the need for the potentially sleep-prone GFP_KERNEL allocations used by ipv6.igmp_sk.

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