CVE-2018-18737 in Douchat
Summary
by MITRE
An XXE issue was discovered in Douchat 4.0.4 because Data\notify.php calls simplexml_load_string. This can also be used for SSRF.
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Analysis
by VulDB Data Team • 04/07/2020
The vulnerability identified as CVE-2018-18737 represents a critical security flaw in the Douchat 4.0.4 web application that stems from improper handling of external XML entities within the Dataotify.php component. This issue manifests through the use of simplexml_load_string function which processes XML data without adequate validation or sanitization, creating a pathway for malicious actors to exploit the system through XML External Entity injection attacks. The vulnerability specifically affects the Dataotify.php file where user-supplied XML input is directly processed without proper security controls, allowing attackers to manipulate the XML parsing behavior and potentially access internal system resources.
The technical implementation of this vulnerability leverages the inherent weaknesses in how PHP's simplexml_load_string function handles external entity references, enabling attackers to craft malicious XML payloads that can trigger various security exploits. When the application processes XML data containing external entity declarations, the parser attempts to resolve these entities which can lead to unauthorized data access, server-side request forgery, or even remote code execution depending on the underlying system configuration. The vulnerability is particularly dangerous because it can be exploited to perform server-side request forgery attacks, where the application makes unintended requests to internal services or external systems, potentially exposing sensitive network infrastructure and data.
From an operational impact perspective, this vulnerability creates significant risks for organizations using Douchat 4.0.4 as it allows attackers to potentially gain unauthorized access to internal network resources, extract sensitive data from the server, or perform reconnaissance activities against internal systems. The SSRF capability amplifies the threat model by enabling attackers to bypass network segmentation controls and access services that should normally be restricted. According to CWE classification, this vulnerability maps to CWE-611 Improper Restriction of XML External Entity Reference, which is a well-documented weakness in XML processing implementations that has been consistently exploited in various web applications. The attack surface is further expanded when considering that the vulnerability can be chained with other exploits to create more sophisticated attack vectors.
Security mitigations for this vulnerability should focus on implementing proper XML input validation and sanitization techniques, specifically by disabling external entity resolution in XML parsers and employing secure coding practices that prevent untrusted XML data from being processed without adequate security controls. Organizations should implement input validation mechanisms that filter or reject XML content containing external entity declarations, and consider using alternative XML processing libraries that provide better security controls out-of-the-box. Additionally, network segmentation and access controls should be implemented to limit the potential impact of successful SSRF attacks, while regular security testing and code reviews should be conducted to identify similar vulnerabilities in other components of the application. The ATT&CK framework categorizes this type of vulnerability under T1213 Data from Information Repositories and T1071.004 Application Layer Protocol: DNS, as attackers may use the vulnerability to extract data or perform reconnaissance activities against internal systems.