# CVE-2026-89564

## Summary

- **CVE ID:** CVE-2026-89564
- **Severity:** HIGH
- **CVSS Score:** 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 13, 2026

## 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.

## Affected Products

- Linux — Linux (cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449)
- Linux — Linux (5.7)
- Linux — Linux (0)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)

## References

- [CNA](https://git.kernel.org/stable/c/a8af6fbac895f057c4b8ff8a2e3fb4c5827fe4ce)
- [CNA](https://git.kernel.org/stable/c/f1281d4b99089fbaf0d3579bba62a814ebb4de4d)
- [CNA](https://git.kernel.org/stable/c/e36ce6e78fe3fc3c071a26750783b7ba081ce10d)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.14%
- **EPSS Percentile:** 3.4

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._