Bug 2568425 (CVE-2026-100081)

Summary: CVE-2026-100081 kernel: kernel: xen-netback: Denial of Service via race condition during interface disconnect
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's Xen network backend (xen-netback) driver. A race condition occurs during network interface disconnection when multicast address memory is freed before active network packet processing has completely stopped. A malicious guest virtual machine can exploit this vulnerability to cause a Denial of Service (DoS) via a host system crash or potentially execute arbitrary code on the host.
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Description OSIDB Bzimport 2026-11-06 18:31:37 UTC 
In the Linux kernel, the following vulnerability has been resolved:

xen-netback: defer xenvif_mcast_addr_list_free()

In order for the function to legitimately avoid locking/RCU, it needs to
run after all TX/RX processing has finished/stopped: Lookups happen from
xenvif_start_xmit(), while adds/removes happen from xenvif_tx_action()
(called out of xenvif_poll()).

Move the call out of xenvif_disconnect_data() (the call to the function
from connect()'s error path doesn't require any cleaning up there), and
put it past the synchronization point in backend_disconnect().

This is XSA-527 / CVE-2026-100081.