# CVE-2026-23011: ipv4: ip_gre: make ipgre_header() robust

> A flaw in the Linux kernel's IPv4 GRE header handling allows local attackers to crash the system via a race condition involving network device headroom changes.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **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:** Yes
- **Published:** 25 Jan 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-77121, BELL-CVE-2026-23011, DEBIAN-CVE-2026-23011, GHSA-5ww3-m3hh-c9fg, ROOT-OS-DEBIAN-11-CVE-2026-23011, ROOT-OS-DEBIAN-12-CVE-2026-23011, ROOT-OS-DEBIAN-13-CVE-2026-23011, ROOT-OS-UBUNTU-2204-CVE-2026-23011, ROOT-OS-UBUNTU-2404-CVE-2026-23011, UBUNTU-CVE-2026-23011

## What is CVE-2026-23011?

CVE-2026-23011 is a medium-severity denial of service vulnerability in Linux kernel, published on 25 Jan 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:

ipv4: ip_gre: make ipgre_header() robust

Analog to commit db5b4e39c4e6 ("ip6_gre: make ip6gre_header() robust")

Over the years, syzbot found many ways to crash the kernel
in ipgre_header() [1].

This involves team or bonding drivers ability to dynamically
change their dev->needed_headroom and/or dev->hard_header_len

In this particular crash mld_newpack() allocated an skb
with a too small reserve/headroom, and by the time mld_sendpack()
was called, syzbot managed to attach an ipgre device.

[1]
skbuff: skb_under_panic: text:ffffffff89ea3cb7 len:2030915468 put:2030915372 head:ffff888058b43000 data:ffff887fdfa6e194 tail:0x120 end:0x6c0 dev:team0
 kernel BUG at net/core/skbuff.c:213 !
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 1 UID: 0 PID: 1322 Comm: kworker/1:9 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: mld mld_ifc_work
 RIP: 0010:skb_panic+0x157/0x160 net/core/skbuff.c:213
Call Trace:
 <TASK>
  skb_under_panic net/core/skbuff.c:223 [inline]
  skb_push+0xc3/0xe0 net/core/skbuff.c:2641
  ipgre_header+0x67/0x290 net/ipv4/ip_gre.c:897
  dev_hard_header include/linux/netdevice.h:3436 [inline]
  neigh_connected_output+0x286/0x460 net/core/neighbour.c:1618
  NF_HOOK_COND include/linux/netfilter.h:307 [inline]
  ip6_output+0x340/0x550 net/ipv6/ip6_output.c:247
  NF_HOOK+0x9e/0x380 include/linux/netfilter.h:318
  mld_sendpack+0x8d4/0xe60 net/ipv6/mcast.c:1855
  mld_send_cr net/ipv6/mcast.c:2154 [inline]
  mld_ifc_work+0x83e/0xd60 net/ipv6/mcast.c:2693
  process_one_work kernel/workqueue.c:3257 [inline]
  process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340
  worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421
  kthread+0x711/0x8a0 kernel/kthread.c:463
  ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158
  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

Weakness: CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer)

## Which versions are affected by CVE-2026-23011?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-23011?

Apply the vendor's patch.

## Is CVE-2026-23011 being exploited?

There is no known exploitation of CVE-2026-23011 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23011 and fix it if it is affected.

What it is: CVE-2026-23011 is a medium-severity denial of service vulnerability in Linux kernel, published on 25 Jan 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-23011 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-23011/ (Markdown: https://insights.sbomify.com/CVE-2026-23011/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23011
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23011
- OSV: https://osv.dev/vulnerability/CVE-2026-23011

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23011/
Summaries are generated and may contain mistakes; the official description above is the record.