CVE-2026-68296 net: gre: fix lltx regression for GRE tunnels with SEQ/CSUM
A regression in Linux kernel GRE tunnel handling causes lockless TX loss, leading to potential ABBA deadlocks and denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-68296?
CVE-2026-68296 is a denial of service vulnerability in Linux, published on 10 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
net: gre: fix lltx regression for GRE tunnels with SEQ/CSUM
Before commit 00d066a4d4ed ("netdev_features: convert NETIF_F_LLTX to dev->lltx"), NETIF_F_LLTX was set unconditionally in both __gre_tunnel_init() and ip6gre_tnl_init_features() alongside GRE_FEATURES:
dev->features |= GRE_FEATURES | NETIF_F_LLTX;
When that commit converted NETIF_F_LLTX to the dev->lltx flag, it placed 'dev->lltx = true' after the SEQ/CSUM early returns instead of before them. This causes GRE/GRETAP/ip6gre tunnels with SEQ or CSUM+encap to lose lockless TX, reintroducing _xmit_lock acquisition around their ndo_start_xmit. Since GRE xmit re-enters the stack via ip_tunnel_xmit(), holding _xmit_lock risks ABBA deadlock with the underlay device.
CPU0 CPU1 ---- ---- lock(&qdisc_xmit_lock_key#6); lock(&qdisc_xmit_lock_key#3); lock(&qdisc_xmit_lock_key#6); lock(&qdisc_xmit_lock_key#3);
Fix by moving dev->lltx = true before the early returns in both functions, restoring the original unconditional behavior.
Which versions are affected by CVE-2026-68296?
How do I fix CVE-2026-68296?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-68296 being exploited?
There is no known exploitation of CVE-2026-68296 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-68296, DEBIAN-CVE-2026-68296, GHSA-2mgg-c98j-9pmm, UBUNTU-CVE-2026-68296.