# CVE-2026-99074: Linux kernel null pointer dereference in IPv4 PMTU update

Source: https://junglewise.ai/threats/cve-2026-99074-in-the-linux-kernel-the-following-vulnerability-has-been-resolved  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-23. Updated: 2026-10-23  
License: CC BY 4.0 with a link back

CVE-2026-99074 · Severity: info · Published 2026-10-23

The Linux kernel's IPv4 routing code can crash when handling Path Maximum Transmission Unit (PMTU) updates on systems using multipath nexthop groups. A local user with CAP_NET_ADMIN capability can trigger a null pointer dereference by manipulating network routing configuration, potentially causing a denial of service.

Technologies: [Linux kernel](https://junglewise.ai/threats/technologies/x-linux-kernel).

## Quick answers

**Is CVE-2026-99074 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-99074 being exploited in the wild.

**How severe is CVE-2026-99074?** Informational severity, published 23 October 2026.

**Which products and versions are affected?** Linux kernel Versions with commit 7d3f3b4367f3 and later, prior to fix commit 6619e01855e65ef35723685a557e3eb106f4ecf5.

**Is there a fix for CVE-2026-99074?** A patch was published on 2026-10-06: Fix committed upstream Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-99074 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-99074?** 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 race condition exists in __ip_rt_update_pmtu() where fib_info_num_path() and fib_info_nhc() independently load nexthop group data protected only by RCU. If a concurrent nexthop group replacement shrinks the group after the loop accepts an index, fib_info_nhc() returns NULL and update_or_create_fnhe() dereferences the NULL pointer. The fix adds a NULL check to break the loop when an indexed path becomes absent. This requires CAP_NET_ADMIN in a network namespace, which unprivileged users can obtain in their own user/network namespace.

## Affected products

- Linux kernel Versions with commit 7d3f3b4367f3 and later, prior to fix commit 6619e01855e65ef35723685a557e3eb106f4ecf5

## Timeline

- 2026-10-23: disclosed
- 2026-10-06: patched: Fix committed upstream
- 2026-10-02: other: Fix authored

## References

- [https://git.kernel.org/stable/c/6619e01855e65ef35723685a557e3eb106f4ecf5](https://git.kernel.org/stable/c/6619e01855e65ef35723685a557e3eb106f4ecf5)
- [https://git.kernel.org/stable/c/7fd60d3c9a1e1b11ef5f1643bbae78d91eae2f4a](https://git.kernel.org/stable/c/7fd60d3c9a1e1b11ef5f1643bbae78d91eae2f4a)

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