CVE-2026-89564
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk3th percentile - higher than 3% of all known CVEs
Summary
A use-after-free vulnerability exists in the Linux kernel's IPv4/IPv6 multicast forwarding path. When a multicast packet is not locally deliverable, the skb retains an skb->sk association set by bpf_sk_assign() or UDP early demux even though a socket reference is not guaranteed. After the prefetched socket is destroyed, a later skb free invokes sock_pfree() and dereferences the stale skb->sk.
Risk Assessment
This can lead to kernel crashes (panic) or potential code execution in kernel context, threatening system stability and security, especially on hosts handling multicast traffic.
Recommendation
Update the Linux kernel to a version containing the fix that orphans the skb before each non-local multicast forwarding path.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: ip: orphan prefetched skbs before multicast forwarding IPv4 and IPv6 input preserve an skb->sk association installed by bpf_sk_assign() so that local delivery can use the selected socket under RCU. Both address families can also prefetch a socket in UDP early demux. In both paths (BPF and UDP early demux) a reference is not guaranteed to be held on the socket. When a multicast packet is not locally deliverable, IPv6 hands the original skb to ip6_mr_input(). IPv4's ip_mr_input() similarly keeps the original skb when local delivery is not needed. Either path can put the skb on an unresolved multicast route queue or forward it after the receive-side RCU section ends. After the prefetched socket is destroyed, a later skb free invokes sock_pfree() and dereferences the stale skb->sk. Orphan the skb before each non-local multicast forwarding path. Local delivery retains the original skb; the existing skb_clone() calls provide multicast forwarding with a socket-free clone.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

