CVE-2026-90111 ip6mr: do not clone dst in ip6mr_cache_report()
A use-after-free in the Linux kernel IPv6 multicast routing allows attackers to trigger memory corruption and potential code execution via crafted packets.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90111?
CVE-2026-90111 is a high-severity use after free vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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().
Which versions are affected by CVE-2026-90111?
How do I fix CVE-2026-90111?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-90111 being exploited?
There is no known exploitation of CVE-2026-90111 in the wild and no public exploit code.
Sources
Also known as AZL-102087, BELL-CVE-2026-90111, DEBIAN-CVE-2026-90111, GHSA-4329-5qmc-m43g, UBUNTU-CVE-2026-90111.