CVE-2026-99041 ip6_gre: remove obsolete ERSPAN PMTU update
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-99041?
CVE-2026-99041 is a vulnerability in Linux, published on 23 Oct 2026.
Official description
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The update is obsolete.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.
Which versions are affected by CVE-2026-99041?
How do I fix CVE-2026-99041?
Upgrade to a fixed version.
Is CVE-2026-99041 being exploited?
There is no known exploitation of CVE-2026-99041 in the wild and no public exploit code.
Sources
Also known as AZL-110918, BELL-CVE-2026-99041, DEBIAN-CVE-2026-99041, GHSA-p22x-mpcm-2h5h, UBUNTU-CVE-2026-99041.