CVE-2018-0108 in WebEx Meetings Server
Summary
by MITRE
A vulnerability in Cisco WebEx Meetings Server could allow an unauthenticated, remote attacker to collect customer files via an out-of-band XML External Entity (XXE) injection. An attacker could exploit this vulnerability to gain information to conduct additional reconnaissance attacks. The vulnerability is due to the ability of an attacker to perform an out-of-band XXE injection on the system, which could allow an attacker to capture customer files and redirect them to another destination address. An exploit could allow the attacker to discover sensitive customer data. Cisco Bug IDs: CSCvg36996.
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Analysis
by VulDB Data Team • 02/01/2021
The vulnerability identified as CVE-2018-0108 affects Cisco WebEx Meetings Server, representing a critical security flaw that enables unauthenticated remote attackers to perform out-of-band XML External Entity injection attacks. This vulnerability resides within the server's processing of XML data, specifically in how it handles external entity references during data parsing operations. The flaw allows attackers to manipulate the XML parser to reference external resources, creating a pathway for unauthorized data exfiltration and reconnaissance activities. The vulnerability is particularly concerning because it does not require authentication credentials for exploitation, making it accessible to any remote attacker with network connectivity to the affected system. Cisco has documented this issue under bug ID CSCvg36996, which provides additional technical context for the specific implementation flaw within the WebEx Meetings Server software.
The technical implementation of this vulnerability stems from improper input validation and XML parsing mechanisms within the Cisco WebEx Meetings Server. When the system processes XML data containing external entity references, it fails to adequately sanitize or restrict these references, allowing attackers to craft malicious XML payloads that can trigger out-of-band XXE behavior. This particular variant of XXE injection operates through out-of-band channels, meaning that the attacker can direct the server to make external network requests to addresses controlled by the attacker, effectively enabling data exfiltration without direct interaction with the server's response. The vulnerability creates a scenario where sensitive customer data can be accessed and potentially redirected to attacker-controlled destinations, providing attackers with valuable reconnaissance information that could facilitate more sophisticated attacks. The flaw specifically impacts the server's ability to properly handle XML external entity declarations and references within incoming data streams, creating an attack surface that can be exploited through various network interfaces.
The operational impact of CVE-2018-0108 extends beyond simple data theft to encompass comprehensive reconnaissance capabilities that could enable attackers to gather intelligence about customer systems and infrastructure. Attackers can leverage this vulnerability to discover sensitive information including customer files, system configurations, and potentially user credentials that may be embedded within XML data structures. The out-of-band nature of the XXE injection allows attackers to exfiltrate data through DNS requests or HTTP connections to attacker-controlled servers, making detection more challenging as the malicious activity appears as legitimate network traffic. This vulnerability directly violates security principles established in the OWASP Top Ten and aligns with CWE-611 (Improper Restriction of XML External Entity Reference) and CWE-20 (Improper Input Validation) categories. Organizations using Cisco WebEx Meetings Server face significant risk of data breaches, regulatory compliance violations, and potential compromise of customer privacy when this vulnerability remains unpatched. The impact is particularly severe for enterprises that handle sensitive information and rely on WebEx for business-critical communications and meetings.
Organizations should implement immediate mitigations including applying the latest security patches from Cisco, which address the specific XXE injection vulnerabilities in the WebEx Meetings Server. Network segmentation and firewall rules should be implemented to restrict access to the WebEx server, particularly blocking external connections that could facilitate out-of-band XXE attacks. Input validation controls should be strengthened to prevent XML external entity references from being processed, and the principle of least privilege should be enforced to limit the system's ability to make external network requests. Security monitoring should be enhanced to detect unusual DNS queries or HTTP requests that may indicate XXE exploitation attempts, with particular attention to outbound connections from the WebEx server to unknown or suspicious destinations. This vulnerability demonstrates the importance of implementing the ATT&CK framework's techniques related to data exfiltration and reconnaissance, as attackers can use such flaws to gather intelligence before launching more targeted attacks. Organizations should also conduct comprehensive vulnerability assessments to identify other potential XXE vulnerabilities in their systems and ensure proper XML parsing configurations that prevent external entity resolution. The incident highlights the critical need for secure coding practices and regular security testing of web applications to prevent similar vulnerabilities from being introduced into production systems.