# CVE-2026-64538: Linux Kernel null pointer dereference in fib6_nh_mtu_change

Source: https://junglewise.ai/threats/cve-2026-64538-linux-kernel-null-pointer-dereference-in-fib6-nh-mtu-change  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-27. Updated: 2026-07-27  
License: CC BY 4.0 with a link back

CVE-2026-64538 · Severity: info · CVSS 6.2 · Published 2026-07-27

A vulnerability was identified in the Linux kernel's IPv6 networking component. The issue occurs when the system processes specific network configuration changes, potentially leading to a system crash (kernel oops). This could result in a denial-of-service, impacting the availability of the affected server or device.

Technologies: [Linux Kernel](https://junglewise.ai/threats/technologies/kernel). Vendors: [Linux](https://junglewise.ai/threats/vendors/linux).

## Quick answers

**Is CVE-2026-64538 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-64538 being exploited in the wild.

**How severe is CVE-2026-64538?** Informational severity, with a CVSS score of 6.2, published 27 July 2026.

**Which products and versions are affected?** Linux Kernel c0b220cf7d80 to 46c3b8191aad (mainline).

**Is there a fix for CVE-2026-64538?** A patch was published on 2026-06-22: Patch merged into mainline kernel Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-64538 attacked?** It is attacked over the network, in an operating system.

**Am I affected by CVE-2026-64538?** Check whether you run Linux Kernel at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A null pointer dereference exists in the fib6_nh_mtu_change() function within net/ipv6/route.c. The vulnerability is caused by an unguarded re-fetch of the 'idev' pointer via __in6_dev_get(arg->dev). During an interface shutdown (addrconf_ifdown), the dev->ip6_ptr can be cleared while a Router Advertisement (RA)-driven MTU update walk is still in progress. Because nexthop-backed routes can survive the initial flush, the walk may attempt to dereference a NULL idev pointer, resulting in a general protection fault. The fix introduces a NULL check to safely return 0 if the device pointer has been cleared.

## Affected products

- Linux Linux Kernel c0b220cf7d80 to 46c3b8191aad (mainline)

## Timeline

- 2026-06-18: disclosed: Initial patch authored
- 2026-06-22: patched: Patch merged into mainline kernel
- 2026-07-27: advisory: CVE published to NVD

## References

- [https://git.kernel.org/stable/c/1451deca9896957159f0666520a792c1b861af4f](https://git.kernel.org/stable/c/1451deca9896957159f0666520a792c1b861af4f)
- [https://git.kernel.org/stable/c/302d57ed7872838b40e56a868fb4c7da7da606e9](https://git.kernel.org/stable/c/302d57ed7872838b40e56a868fb4c7da7da606e9)
- [https://git.kernel.org/stable/c/46c3b8191aad3d032776bf3bebf03efdf5f4b905](https://git.kernel.org/stable/c/46c3b8191aad3d032776bf3bebf03efdf5f4b905)
- [https://git.kernel.org/stable/c/6428634f7a0b7878144b4925c37856bef3224967](https://git.kernel.org/stable/c/6428634f7a0b7878144b4925c37856bef3224967)
- [https://git.kernel.org/stable/c/80600b5d0f3ecb9324120dc95b5e915130f516c5](https://git.kernel.org/stable/c/80600b5d0f3ecb9324120dc95b5e915130f516c5)
- [https://git.kernel.org/stable/c/b0d0eb13a0441a8ebf4f227843deaf494f1e2c33](https://git.kernel.org/stable/c/b0d0eb13a0441a8ebf4f227843deaf494f1e2c33)
- [https://git.kernel.org/stable/c/b2c70dd3326809429b709a9c7e9220d29923051a](https://git.kernel.org/stable/c/b2c70dd3326809429b709a9c7e9220d29923051a)

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