CVE-2022-45440 in AX7501-B0
Summary
by MITRE • 01/17/2023
A vulnerability exists in the FTP server of the Zyxel AX7501-B0 firmware prior to V5.17(ABPC.3)C0, which processes symbolic links on external storage media. A local authenticated attacker with administrator privileges could abuse this vulnerability to access the root file system by creating a symbolic link on external storage media, such as a USB flash drive, and then logging into the FTP server on a vulnerable device.
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Analysis
by VulDB Data Team • 12/17/2025
This vulnerability in the Zyxel AX7501-B0 firmware represents a critical path traversal flaw that exploits improper handling of symbolic links within external storage media. The issue stems from insufficient validation of file system objects when processing FTP requests, allowing malicious actors with administrative credentials to manipulate the system's file access mechanisms. The vulnerability specifically affects firmware versions prior to V5.17(ABPC.3)C0 and demonstrates a fundamental failure in the device's security model when dealing with external storage inputs. The flaw enables an attacker to escalate privileges and gain unauthorized access to the root file system through a carefully crafted symbolic link attack.
The technical implementation of this vulnerability involves the FTP server's processing of symbolic links that are created on external storage devices such as USB flash drives. When an authenticated administrator creates a symbolic link pointing to system directories on external media, the FTP server fails to properly validate the target path, allowing the attacker to traverse the file system hierarchy. This represents a classic case of inadequate input sanitization and path validation, where the system does not properly resolve symbolic links before granting access permissions. The vulnerability operates at the intersection of file system access controls and network service security, creating an attack vector that bypasses normal authentication mechanisms.
The operational impact of this vulnerability is severe as it provides a direct path to system compromise for any attacker with administrative credentials. Once exploited, the attacker gains access to the root file system, which typically contains sensitive system configuration files, user credentials, and potentially other critical data. This level of access enables the attacker to modify system files, install malicious software, and potentially escalate privileges further. The vulnerability is particularly concerning because it requires only local administrative access to be exploited, making it accessible to insiders or attackers who have already compromised administrative credentials. The attack can be executed through simple file creation operations on external storage media, making it both accessible and difficult to detect.
Mitigation strategies for this vulnerability should focus on firmware updates to version V5.17(ABPC.3)C0 or later, which contain the necessary patches to properly validate symbolic links and prevent path traversal attacks. Organizations should also implement strict access controls and monitoring of external storage devices connected to the network, particularly those used with FTP services. Network segmentation and privilege separation can help limit the impact if the vulnerability is exploited, while regular security audits should verify that no malicious symbolic links have been created on external media. The vulnerability aligns with CWE-22 Path Traversal and CWE-73 Improper Neutralization of Special Elements in Output Used by a Downstream Component, and represents a technique that could be categorized under ATT&CK tactic TA0006 Credential Access and TA0003 Persistence, as it enables unauthorized access to system resources and potential long-term compromise of the affected device.