Live › vulnerability › CVE-2026-99041
Go to dashboardA tc tunnel_key action combined with mirred redirect to a native ip6erspan device makes the kernel dereference a NULL device pointer while handling path MTU updates. The reported result is a kernel panic (denial of service) triggered from an unprivileged user with self-created namespaces.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-23 21:57 UTC. All times on this page are UTC.
Only systems that load the IPv6 GRE/ERSPAN tunnel driver and use ERSPAN tunnel devices with tc tunnel_key and mirred redirection are exposed. Hosts that do not use ip6erspan devices can skip it, and the sources say the reproduction was on a development kernel v7.2 with KASAN.
No product ranges from the sources yet.
uname -r and compare against the kernel version that contains the upstream fix, which the sources do not namelsmod | grep ip6_gre to see whether the ip6_gre/ip6erspan module is loaded at allsysctl kernel.unprivileged_userns_clone or sysctl user.max_user_namespacesmodprobe -r ip6_greEach row is the first time that source carried this signal. The analyst’s rows are its own findings.
In the Linux kernel, the following vulnerability has been resolved:
ip6_gre: remove obsolete ERSPAN PMTU update
A tc tunnel_key action can attach a METADATA_IP_TUNNEL dst to an skb, and mirred can redirect it to a native ip6erspan device. The legacy PMTU update in ip6erspan_tunnel_xmit() treats that metadata dst as a route. Since it has no output device, dst_dev(dst)->mtu dereferences NULL.
On v7.2 with KASAN, an initial UID/GID 65534 process with CapEff 0 used self-created user and network namespaces to trigger:
KASAN: null-ptr-deref RIP: ip6erspan_tunnel_xmit+0x10fc/0x2cc0 Kernel panic - not syncing: Fatal exception in interrupt
The update is obsolete. Commit fe1a4ca0a2b7 ("ip6_gre: process toobig in a better way") changed IPv6 GRE Too Big handling to update the underlay route and removed the equivalent block from __gre6_xmit(). ip6_tnl_xmit() then propagates the underlay PMTU to the overlay route.
Remove the stale ERSPAN copy and its now-unused dst variable. This eliminates the metadata-dst dereference and keeps ERSPAN aligned with IPv6 GRE PMTU handling.
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