CVE-2026-89564: Linux Vulnerability (CVSS 7.8)

Description

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.

Metrics

CVSS 3.1

7.8/10

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

0.14%

3.4th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449, < e62aef7d6a5b27569bf540bbe11a9482117ff588; >= cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449, < a8af6fbac895f057c4b8ff8a2e3fb4c5827fe4ce; >= cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449, < f1281d4b99089fbaf0d3579bba62a814ebb4de4d; >= cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449, < e36ce6e78fe3fc3c071a26750783b7ba081ce10d
Linux	Linux	5.7

References

Timeline

Published: Sep 11, 2026
Last Modified: Sep 21, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-89564?

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.

How severe is CVE-2026-89564?

CVE-2026-89564 has a CVSS score of 7.8/10 (HIGH severity). The EPSS model estimates a 0.14% probability of exploitation in the next 30 days.

How do I fix CVE-2026-89564?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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