CVE-2026-98493: net: ipconfig: bound DHCP option construction

Published Oct 18, 2026

Updated

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

net: ipconfig: bound DHCP option construction

icdhcpinitoptions() appends the hostname (option 12), vendor-class (option 60) and client-ID (option 61) options into the fixed 312-byte bootppkt.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 CONFIGFORTIFYSOURCE this is reported as a field-spanning write and, when the kernel is booted with paniconwarn=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.

Affected Software

1 affected component

Linux Linux kernel

Event History

Oct 18, 2026

CVE Published

via MITRE·03:16 PM

Data Sourced

via MITRE·03:16 PM

Description

Data Sourced

via NVD·04:17 PM

Description

Frequently Asked Questions

What configuration is needed to trigger the overflow?

The kernel must be constructing DHCP options with optional hostname, vendor-class, or client-ID values. A 64-byte hostname combined with a 252-byte dhcpclass vendor-class identifier requires more than the 312-byte extension buffer before accounting for the END marker.

What is the operational impact on systems using FORTIFY_SOURCE?

CONFIG_FORTIFY_SOURCE reports the out-of-bounds vendor-class write as a field-spanning write. If the kernel is also booted with panic_on_warn=1, that warning causes a boot-time kernel panic.

What can be done before applying the fix?

Keep the configured DHCP hostname and vendor-class values short enough that all optional DHCP options, their two-byte headers, and the END marker fit in the 312-byte buffer. The described oversized combination should be avoided.

How can I recognize that this issue has occurred?

On kernels built with CONFIG_FORTIFY_SOURCE, the condition is reported as a field-spanning write during boot. Systems with panic_on_warn=1 may instead fail to boot because the warning triggers a panic.

CVE-2026-98493: net: ipconfig: bound DHCP option construction

Affected Software

Event History

Frequently Asked Questions

What configuration is needed to trigger the overflow?

What is the operational impact on systems using FORTIFY_SOURCE?

What can be done before applying the fix?

How can I recognize that this issue has occurred?

Company

Resources

Contact

Frequently Asked Questions

What configuration is needed to trigger the overflow?

What is the operational impact on systems using FORTIFY_SOURCE?

What can be done before applying the fix?

How can I recognize that this issue has occurred?