Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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Executive Summary

CVE-2026-42511 is a critical vulnerability in the dhclient(8) component of FreeBSD. It occurs because the BOOTP file field in DHCP responses is written to the lease file without escaping embedded double-quotes. This flaw allows an attacker to inject arbitrary dhclient.conf directives into the lease file.

When the lease file is re-parsed, for example after a system restart, these injected directives are processed by dhclient-script(8), which executes them with root privileges. This means an attacker controlling a rogue DHCP server on the same broadcast domain can execute arbitrary code as root on the affected system.

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Impact Analysis

This vulnerability allows a rogue DHCP server to execute arbitrary code with root privileges on a vulnerable FreeBSD system running dhclient. An attacker can send malicious DHCP responses that inject harmful directives into the lease file, which are then executed upon lease file re-parsing.

The impact is severe as it grants full control over the affected system to an attacker on the same broadcast domain, potentially leading to system compromise, data theft, or further network attacks.

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Mitigation Strategies

To mitigate the vulnerability CVE-2026-42511, network administrators should implement DHCP snooping on switches to block rogue DHCP servers from sending malicious DHCP responses.

Additionally, users should upgrade their FreeBSD systems to the patched versions available for stable/15, stable/14, stable/13, and their respective release branches.

Upgrades can be performed using pkg(8), freebsd-update(8), or by applying the source code patches provided by the FreeBSD Project.

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Detection Guidance

This vulnerability involves a rogue DHCP server sending malicious DHCP responses with specially crafted BOOTP file fields to inject arbitrary directives into the dhclient lease file. Detection involves monitoring for unauthorized DHCP servers on the network and inspecting DHCP lease files for suspicious entries containing unescaped double-quotes or unexpected directives.

To detect rogue DHCP servers on your network, you can use network scanning tools or commands such as:

• Use the command `tcpdump -i <interface> port 67 or port 68` to capture DHCP traffic and look for unexpected DHCP offer or ACK packets.
• Use `dhclient -v` to run the DHCP client in verbose mode and observe the lease negotiation process for suspicious BOOTP file field values.
• Inspect the DHCP lease file (commonly located at `/var/db/dhclient.leases` or similar) for entries containing unescaped double-quotes or unusual directives that could indicate injection.

Additionally, implementing DHCP snooping on network switches can help block rogue DHCP servers and prevent exploitation.

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