CVE-2026-75168 in X-Serie Gateway
Summary
by MITRE • 09/04/2026
An issue in the ugw-editfile method of /cgi-bin/wwwugw.cgi in MBS-Solutions X-Serie Gateway firmware V6_00_05 allows a remote authenticated user with the low-privileged Standard role to write arbitrary content to files within /uxx/config/ and /ugw/config/.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability identified involves an insecure file writing mechanism within the MBS-Solutions X-Series Gateway firmware, specifically affecting version V6_00_05. The flaw resides in the ugw-editfile method exposed through the web interface at the path /cgi-bin/wwwugw.cgi. This component is designed to allow administrators or users with appropriate privileges to modify configuration files via a graphical user interface. However, the implementation fails to enforce strict access controls and input validation when handling file write operations. Consequently, an attacker who has successfully authenticated with a low-privileged Standard role can exploit this weakness to overwrite critical system configuration files located in the /uxx/config/ and /ugw/config/ directories. This represents a significant deviation from the principle of least privilege, as standard users are granted capabilities that should be reserved for high-level administrators or root accounts.
From a technical perspective, the core issue is classified under CWE-434, which describes the unrestricted upload of file with dangerous type, although in this specific context it manifests more accurately as CWE-276: Incorrect Default Permissions and CWE-285: Improper Authorization. The vulnerability allows for arbitrary file write operations because the backend script does not adequately verify whether the authenticated user possesses the necessary administrative rights to modify files outside their designated scope. Furthermore, there appears to be a lack of robust path traversal prevention or content validation mechanisms that would restrict writes to only specific, whitelisted configuration parameters rather than allowing raw content injection into arbitrary system paths. This oversight enables an attacker to manipulate internal settings by directly editing the underlying configuration files stored on the device's filesystem.
The operational impact of this vulnerability is severe and multifaceted. By gaining write access to critical configuration directories such as /ugw/config/, a low-privileged user can alter network routing tables, firewall rules, DNS settings, or authentication mechanisms. This capability effectively allows an attacker to escalate their privileges indirectly by modifying system parameters that control security policies. For instance, they could disable intrusion detection systems, open unauthorized ports for reverse shells, or redirect traffic through malicious intermediaries. Additionally, if the configuration files contain sensitive data such as API keys, passwords, or cryptographic certificates, these assets are compromised. The ability to persist changes in these directories means the impact is not limited to a single session but can survive device reboots, leading to long-term compromise of the network infrastructure protected by this gateway.
This vulnerability aligns with several tactics and techniques within the MITRE ATT&CK framework for enterprise networks. It directly relates to T1078: Valid Accounts, as it relies on legitimate credentials obtained through phishing or credential stuffing attacks against low-privileged users. The exploitation method falls under T1222: File and Directory Permissions Modification, where an attacker alters permissions or contents of files to facilitate further malicious activity. Furthermore, the ability to modify configuration settings maps to T1562: Impair Defenses, as it allows for the disabling or bypassing of security controls embedded in the gateway's firmware. The persistence achieved through writing to /uxx/config/ also touches upon T1034: Internal Spearphishing if used to spread malware via modified system scripts, though primarily it serves as a mechanism for maintaining control over the compromised device.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary solution is to apply the firmware update provided by MBS-Solutions that patches this specific authorization flaw in the ugw-editfile method. Until an official patch is available, administrators should restrict network access to the management interface of these gateways using strict firewall rules, ensuring only trusted IP addresses can reach /cgi-bin/wwwugw.cgi. Additionally, implementing role-based access control (RBAC) with rigorous separation of duties is essential; standard users should never be granted write permissions to system configuration directories. Input validation must also be strengthened on the server side to ensure that file paths are canonicalized and restricted to a predefined whitelist of allowable files. Regular auditing of user privileges and monitoring for unauthorized modifications to critical config files can help detect exploitation attempts early.