CVE-2018-3969
Description
An exploitable vulnerability exists in the verified boot protection of the CUJO Smart Firewall. It is possible to add arbitrary shell commands into the dhcpd.conf file, that persist across reboots and firmware updates, and thus allow for executing unverified commands. To trigger this vulnerability, a local attacker needs to be able to write into /config/dhcpd.conf.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
A local attacker with write access to /config/dhcpd.conf on the CUJO Smart Firewall can inject arbitrary shell commands that persist across reboots and firmware updates.
Vulnerability
The CUJO Smart Firewall (firmware version 7003) contains an exploitable vulnerability in its verified boot protection. A local attacker can add arbitrary shell commands into the /config/dhcpd.conf file. These commands persist across reboots and firmware updates, effectively bypassing verified boot security measures and allowing execution of unverified commands [1].
Exploitation
To exploit this vulnerability, an attacker needs local access to the device and the ability to write to the /config/dhcpd.conf file. This requires prior compromise of the filesystem (e.g., via another vulnerability or physical access). The attacker can then insert arbitrary shell commands into the DHCP configuration file; on subsequent reboots or firmware updates, those commands are executed without verification [1].
Impact
Successful exploitation allows an attacker to execute arbitrary shell commands with elevated privileges on the device. This can lead to full compromise of the firewall, including disclosure of sensitive data, modification of device behavior, and potential use as a pivot point to attack the home network [1].
Mitigation
No official fix or patched firmware version has been disclosed in the available references. Users should restrict local access to the device, monitor file integrity of /config/dhcpd.conf, and consider replacing the device if it remains unpatched [1].
AI Insight generated on May 26, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.
Affected products
1Patches
0No patches discovered yet.
Vulnerability mechanics
Root cause
"The DHCP configuration file `/config/dhcpd.conf` allows `execute()` statements in `on commit` event blocks, and the file persists across reboots and firmware updates without integrity verification."
Attack vector
A local attacker who can write to `/config/dhcpd.conf` can insert an `on commit` event block containing an `execute()` statement. When the DHCP server subsequently leases an IP address, the `on commit` event triggers, executing arbitrary shell commands with root privileges [ref_id=1]. The attacker can store a malicious script (e.g., `/config/root.sh`) in the same partition and have it called by the dhcpd daemon. To prevent the smartphone app from overwriting the modified configuration, the attacker can set the immutable attribute on the file using `chattr +i` [ref_id=1].
Affected code
The vulnerability lies in the DHCP server configuration file `/config/dhcpd.conf`. This file is used by ISC DHCP when the CUJO Smart Firewall operates in "dhcp" mode. The file is normally preserved across reboots and firmware updates because it resides on the `/config` partition, which is not formatted during standard updates [ref_id=1].
What the fix does
The advisory does not include a patch or specific remediation from the vendor. It notes that the vulnerability was disclosed on 2018-07-20 and publicly released on 2019-03-19 [ref_id=1]. The recommended mitigation implied by the advisory is to prevent unauthorized write access to `/config/dhcpd.conf` or to avoid allowing `execute()` statements in the DHCP configuration. No fix commit is published in the bundle.
Preconditions
- inputAttacker must have local access and be able to write to /config/dhcpd.conf
- configCUJO must be operating in 'dhcp' mode so that ISC DHCP reads the configuration file
Reproduction
Add the following lines to `/config/dhcpd.conf`:
``` on commit { execute("/bin/sh", "/config/root.sh"); } ```
Place the attacker's script at `/config/root.sh`. To prevent the smartphone app from overwriting the modified config, run `chattr +i /config/dhcpd.conf`. When a DHCP lease is issued, the `on commit` event executes the script with root privileges [ref_id=1].
Generated on May 25, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.
References
1- talosintelligence.com/vulnerability_reports/TALOS-2018-0634mitrex_refsource_MISC
News mentions
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