CVE-2026-57155 in OPNsense
Summary
by MITRE • 10/15/2026
OPNsense is a FreeBSD based firewall and routing platform. Prior to version 26.1.11, the Firewall Alias GeoIP importer's process_zip() and process_gzip() paths in src/opnsense/scripts/filter/lib/alias/geoip.py use an unvalidated CSV country_code value to construct output filenames below /usr/local/share/GeoIP/alias. A user with Firewall Alias Edit privilege can configure an attacker-controlled GeoIP source URL and supply an archive whose country code traverses into another existing directory, causing attacker-controlled content to be written as root with an -IPv4 or -IPv6 suffix. A crafted newsyslog fragment and oversized log file can use the default hourly root cron job to execute commands as root, resulting in complete firewall compromise. This issue is fixed in version 26.1.11.
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Analysis
by VulDB Data Team • 10/15/2026
OPNsense serves as a widely deployed FreeBSD-based firewall and routing platform that relies on robust security controls to protect network perimeters. A critical vulnerability was identified within the Firewall Alias GeoIP importer functionality, specifically affecting versions prior to 26.1.11. The core technical flaw resides in the process_zip() and process_gzip() methods located in the source file src/opnsense/scripts/filter/lib/alias/geoip.py. These functions are responsible for parsing archive files containing geographic IP data but fail to properly validate or sanitize the country_code value extracted from CSV entries within those archives. This lack of input validation allows an attacker to manipulate the filename construction logic by injecting directory traversal sequences into the country code field.
The operational impact of this flaw is severe due to the execution context and privilege levels involved. When a user possessing Firewall Alias Edit privileges configures a custom GeoIP source URL, they can point it toward an archive controlled by an adversary. By supplying an archive where the CSV entries contain crafted country codes with path traversal characters such as ../, the application constructs output filenames that escape the intended directory /usr/local/share/GeoIP/alias. Consequently, attacker-controlled content is written to arbitrary locations on the filesystem with root privileges, appending either -IPv4 or -IPv6 suffixes based on the IP version. This represents a classic path traversal vulnerability leading to unauthorized file write operations under elevated permissions, which aligns with CWE-22: Improper Limitation of a Pathname to a Restricted Directory and CWE-94: Improper Control of Generation of Code (Code Injection).
The severity escalates significantly when combined with log rotation mechanisms. An attacker can exploit the ability to write files as root by creating a crafted newsyslog configuration fragment alongside an oversized log file in a location accessible via the traversal vulnerability. The default hourly cron job running as root processes these logs, triggering the execution of commands specified within the malicious newsyslog fragment. This chain of exploitation allows for arbitrary command execution with root privileges on the firewall appliance itself. Such access results in complete compromise of the firewall infrastructure, enabling attackers to bypass network security controls, intercept traffic, or pivot into internal networks without detection.
This vulnerability maps directly to MITRE ATT&CK techniques involving Initial Access and Privilege Escalation. Specifically, it relates to T1059: Command and Scripting Interpreter through the execution of arbitrary commands via log rotation abuse, and T1078: Valid Accounts by leveraging legitimate user privileges for Firewall Alias editing to initiate the attack chain. The exploitation path demonstrates how a seemingly minor input validation error in a utility script can be chained with system configuration features like newsyslog to achieve full system compromise.
To mitigate this risk, organizations running OPNsense must immediately upgrade to version 26.1.11 or later where these code paths have been patched to enforce strict validation of country codes and restrict file output to the designated alias directory. Until upgrading is possible, administrators should review user privileges carefully, ensuring that only trusted personnel with Firewall Alias Edit rights can configure external GeoIP sources. Additionally, monitoring for unusual log rotation configurations or unexpected files appearing in system directories outside standard paths may help detect attempted exploitation of this vulnerability in real-time. Regular audits of cron jobs and newsyslog configurations are also recommended to ensure no unauthorized command execution vectors exist on the host system.