CVE-2017-15805 in Small Business SA520
Summary
by MITRE
Cisco Small Business SA520 and SA540 devices with firmware 2.1.71 and 2.2.0.7 allow ../ directory traversal in scgi-bin/platform.cgi via the thispage parameter, for reading arbitrary files.
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Analysis
by VulDB Data Team • 11/30/2019
The vulnerability identified as CVE-2017-15805 affects Cisco Small Business SA520 and SA540 network security appliances running specific firmware versions. This directory traversal flaw exists within the scgi-bin/platform.cgi component of these devices, representing a critical security weakness that allows unauthorized access to sensitive system information. The vulnerability stems from inadequate input validation mechanisms that fail to properly sanitize user-supplied parameters, creating an opportunity for attackers to manipulate file access requests through maliciously crafted URLs.
The technical implementation of this vulnerability involves the exploitation of the thispage parameter within the platform.cgi script, which processes user requests without sufficient validation of directory path inputs. When an attacker submits a request containing directory traversal sequences such as "../", the system fails to properly filter these inputs, allowing the attacker to navigate beyond the intended directory boundaries and access arbitrary files on the device filesystem. This flaw directly maps to CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with the ability to read sensitive configuration files, system logs, and potentially authentication credentials stored on the device. Network administrators and security personnel must recognize that this vulnerability can be exploited to gain unauthorized access to the device's internal structure, potentially leading to complete compromise of the network security appliance. The affected firmware versions 2.1.71 and 2.2.0.7 indicate that this vulnerability has persisted across multiple iterations, suggesting a fundamental flaw in the device's input handling mechanisms.
From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1083, which covers discovering file and directory permissions. Attackers can leverage this weakness to enumerate system files and potentially identify additional attack vectors. The vulnerability affects network infrastructure devices that are often overlooked in security assessments, making it particularly dangerous as these appliances typically operate in privileged network segments. The exploitation requires minimal technical skill, as the attack vector is accessible through standard web browser interactions, making it a prime target for automated exploitation tools.
Organizations should implement immediate mitigations including firmware updates to versions that address the directory traversal vulnerability, network segmentation to limit access to these devices, and monitoring for suspicious directory traversal attempts in web server logs. The vulnerability demonstrates the importance of proper input validation and the principle of least privilege in network security appliance design. Security teams must also consider implementing web application firewalls to detect and block malicious directory traversal attempts, as well as conducting regular vulnerability assessments of network infrastructure devices to identify similar flaws that may exist in other components of the network security stack.