# 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.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-68296, DEBIAN-CVE-2026-68296, GHSA-2mgg-c98j-9pmm, UBUNTU-CVE-2026-68296

## 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.

## Is CVE-2026-68296 being exploited?

There is no known exploitation of CVE-2026-68296 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68296 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-68296 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-68296/ (Markdown: https://insights.sbomify.com/CVE-2026-68296/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68296
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68296
- OSV: https://osv.dev/vulnerability/CVE-2026-68296

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68296/
Summaries are generated and may contain mistakes; the official description above is the record.