Bug 2541027 (CVE-2026-98026)

Summary: CVE-2026-98026 kernel: net: bridge: mcast: properly convert mglist to rcu
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's network bridge subsystem. An attacker could exploit this vulnerability to cause a Denial of Service (DoS) or system crash through a use-after-free condition. This issue occurs during multicast port group removal, where the kernel immediately frees data structures without waiting for concurrent list readers to finish processing.
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Embargoed:

Description OSIDB Bzimport 2026-09-25 10:44:31 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net: bridge: mcast: properly convert mglist to rcu

Sashiko reported a bug [1] that br_multicast_del_port_group unlists the
port group not using proper rcu helper that preserves the next pointer and
after that immediately frees the port group without waiting for rcu grace
period. The only rcu walker of mglist is br_multicast_list_adjacent() and
it turns out that function has always been buggy because mglist was never
properly converted to RCU. Fix it by converting it to rcu and moving its
initialization after eth_addr's. Initializing p->next can use
RCU_INIT_POINTER because we have a barrier from the hlist_add_head_rcu call
later, besides we're initializing an unpublished structure anyway.

[1] https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260826014200.362304-1-littleddfu%40gmail.com
Comment 1 Keith Grant 2026-09-28 21:28:15 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98026.mbox