Bug 2536368 (CVE-2026-90111)

Summary: CVE-2026-90111 kernel: ip6mr: do not clone dst in ip6mr_cache_report()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
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 IPv6 multicast routing (ip6mr) component. This use-after-free vulnerability occurs when a non-refcounted destination entry is improperly handled after being freed. A remote attacker could potentially exploit this by sending specially crafted IPv6 multicast packets, leading to system instability, denial of service, or potentially arbitrary code execution.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Description OSIDB Bzimport 2026-09-17 17:34:12 UTC 
In the Linux kernel, the following vulnerability has been resolved:

ip6mr: do not clone dst in ip6mr_cache_report()

IPv6 input attaches a non-refcounted (NOREF) dst to skbs under RCU.
When an ingress multicast packet misses MFC lookup,
ip6mr_cache_unresolved() places the skb onto the unresolved queue,
escaping the receive-side RCU grace period.

If the underlying route is deleted and freed, and the MFC queue is later
resolved with a wrong parent interface, ip6_mr_forward() invokes
ip6mr_cache_report(..., MRT6MSG_WRONGMIF), which executes
dst_clone(skb_dst(pkt)) on the freed dst entry, triggering a slab
use-after-free.

Report packets queued to mroute6_sk (a raw socket) and netlink
notifications do not require an attached dst entry.

Fix this by:
1. Removing dst_clone() in ip6mr_cache_report() and ensuring report skbs
   do not hold a dst.
2. Dropping skb_dst before queuing unresolved skbs in
   ip6mr_cache_unresolved(), matching the fact that multicast
   forwarding resolves outgoing routes anew via ip6_route_output().
Comment 1 Keith Grant 2026-09-22 22:49:14 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-90111.mbox