OPNsense up to 26.1.10/26.4.1p0 Dnsmasq dnsmasq.conf filename/servername/address/value/mail password os command injection

Summaryinfo

A vulnerability was found in OPNsense up to 26.1.10/26.4.1p0. It has been declared as problematic. This affects an unknown part of the file /usr/local/etc/dnsmasq.conf of the component Dnsmasq/Monit/OpenVPN/DHCPv6/Unbound/IPsec/NTP/PPP/MPD/WebGUI. Such manipulation of the argument filename/servername/address/value/mail password leads to os command injection. This vulnerability is referenced as CVE-2026-57154. It is possible to launch the attack remotely. No exploit is available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in OPNsense up to 26.1.10/26.4.1p0 and classified as problematic. Affected by this issue is some unknown processing of the file /usr/local/etc/dnsmasq.conf of the component Dnsmasq/Monit/OpenVPN/DHCPv6/Unbound/IPsec/NTP/PPP/MPD/WebGUI. The manipulation of the argument filename/servername/address/value/mail password with an unknown input leads to a os command injection vulnerability. Using CWE to declare the problem leads to CWE-78. The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component. Impacted is integrity, and availability. CVE summarizes:

OPNsense is a FreeBSD based firewall and routing platform. Prior to 26.1.11 and 26.4.1p1, authenticated Web UI or API users with delegated access to affected settings can submit CR or LF characters in fields expected to contain one line, causing generated privileged service configuration files to contain additional attacker-controlled directives or policy lines. The confirmed Dnsmasq path includes dhcp_boot.filename, dhcp_boot.servername, dhcp_boot.address, and dhcp_options.value, which are rendered into /usr/local/etc/dnsmasq.conf; access through page-services-dnsforwarder covers api/dnsmasq/*. Related affected fields span OpenVPN, DHCPv6, Unbound, IPsec, NTP, PPP or MPD, Monit, firewall, sudo, WebGUI, and System General configuration. Applying or restarting the affected service can alter behavior beyond the delegated setting, create service-side files, cross RBAC boundaries, or cause denial of service. Line injection through Monit mail password and adjacent Monit text fields into /usr/local/etc/monitrc demonstrated root command execution. Arbitrary shell command execution was not confirmed for the Dnsmasq path. This issue is fixed in versions 26.1.11 and 26.4.1p1.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-57154 since 06/24/2026. The exploitation is known to be easy. The attack may be launched remotely. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1202.

Upgrading to version 26.1.11 or 26.4.1p1 eliminates this vulnerability.

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Productinfo

Name

• OPNsense

Version

• 26.1.0
• 26.1.1
• 26.1.2
• 26.1.3
• 26.1.4
• 26.1.5
• 26.1.6
• 26.1.7
• 26.1.8
• 26.1.9
• 26.1.10
• 26.4.1p0

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