---
id: "CVE-2026-98493"
kind: "vulnerability"
aliases: ["CVE-2026-98493"]
title: "Linux kernel: DHCP option overflow in ipconfig can crash boot"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["infrastructure", "linux-kernel", "network-boot", "self-hosted"]
not_affected_if: ["default-config", "no-kernel-ip-autoconfig"]
published_at: "2026-10-18T16:17:00+00:00"
first_seen_at: "2026-10-23T21:57:15+00:00"
updated_at: "2026-10-25T05:25:41+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98493", "first_seen_at": "2026-10-23T21:57:15+00:00"}]
---

# Linux kernel: DHCP option overflow in ipconfig can crash boot

The Linux kernel's ipconfig code writes the hostname and vendor-class DHCP options into a fixed 312-byte buffer without checking bounds. With a long hostname and a long dhcpclass= boot parameter, the write runs past the buffer, which the kernel reports as a fortified write and, with panic_on_warn=1, aborts boot.

_Summary, check and fix written by a model from the sources; labelled as such._

## Timeline

- 2026-10-23T21:57:15+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98493

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

net: ipconfig: bound DHCP option construction

ic_dhcp_init_options() appends the hostname (option 12), vendor-class
(option 60) and client-ID (option 61) options into the fixed 312-byte
bootp_pkt.exten[] buffer.  Only the client-ID branch checked the
remaining space; the hostname and vendor-class writes were unbounded.

A 64-byte hostname together with the maximum 252-byte dhcpclass=
identifier needs 18 + (2 + 64) + (2 + 252) = 338 of the 312 available
bytes even before the terminating END marker, so the vendor-class memcpy
runs past the end of exten[].  With CONFIG_FORTIFY_SOURCE this is
reported as a field-spanning write and, when the kernel is booted with
panic_on_warn=1, aborts boot with a panic.

Route the optional options through a common helper that makes sure the
option, its 2-byte header and the END marker all fit and drops an option
that would not.  Configurations with short options keep sending exactly
the same bytes as before.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_