CVE-2018-20000 in bw-webdav
Summary
by MITRE
Apereo Bedework bw-webdav before 4.0.3 allows XXE attacks, as demonstrated by an invite-reply document that reads a local file, related to webdav/servlet/common/MethodBase.java and webdav/servlet/common/PostRequestPars.java.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 06/13/2023
The vulnerability identified as CVE-2018-20000 affects Apereo Bedework bw-webdav versions prior to 4.0.3 and represents a critical XML External Entity processing flaw that enables unauthorized file access through carefully crafted webdav requests. This vulnerability resides within the webdav/servlet/common/MethodBase.java and webdav/servlet/common/PostRequestPars.java components of the affected software, where insufficient input validation allows malicious actors to inject external entity references that can traverse the file system and retrieve sensitive local files. The flaw specifically manifests when processing invite-reply documents, which are commonly used in calendar and scheduling applications to respond to meeting invitations, making this attack vector particularly dangerous in collaborative environments where such documents are frequently exchanged.
The technical implementation of this vulnerability stems from improper handling of XML parsing within the webdav servlet components, where the application fails to disable external entity resolution during XML document processing. This weakness allows attackers to craft malicious XML payloads that reference external entities pointing to local files, enabling them to read arbitrary files from the server's file system. The vulnerability is classified under CWE-611, which specifically addresses Improper Restriction of XML External Entity Reference, and aligns with ATT&CK technique T1213.002 for Data from Information Repositories, as it facilitates unauthorized data access through information repository exploitation. The attack requires minimal privileges and can be executed through standard webdav protocols, making it particularly dangerous as it can be exploited by unauthenticated users against vulnerable systems.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can potentially lead to complete system compromise when combined with other attack vectors. An attacker who successfully exploits this vulnerability can access sensitive configuration files, database credentials, application source code, and other confidential data stored locally on the server. The vulnerability is especially concerning in enterprise environments where Bedework is deployed for calendar and scheduling services, as it could expose organizational calendars, meeting details, and user information. The affected components are part of the webdav servlet infrastructure that handles calendar invitations and responses, making this vulnerability particularly relevant for organizations relying on calendar synchronization and collaboration features. Additionally, the vulnerability may enable attackers to perform further reconnaissance, identify system configurations, and potentially escalate privileges through the exposure of sensitive system information.
Organizations should immediately upgrade to Apereo Bedework bw-webdav version 4.0.3 or later, which includes proper XML external entity handling and disables external entity resolution during XML processing. System administrators should also implement network-level controls to restrict access to webdav endpoints and monitor for suspicious XML traffic patterns. The mitigation strategy should include disabling external entity resolution in all XML parsers and implementing proper input validation for all XML processing components. Additional defensive measures include deploying web application firewalls to detect and block malicious XML payloads, implementing strict access controls for webdav endpoints, and conducting regular security assessments of calendar and collaboration systems. Organizations should also consider implementing file access controls and privilege separation to limit the potential impact of successful exploitation, as well as establishing monitoring procedures to detect unauthorized file access attempts that could indicate exploitation of this vulnerability.