CVE-2018-8010 in Solr
Summary
by MITRE
This vulnerability in Apache Solr 6.0.0 to 6.6.3, 7.0.0 to 7.3.0 relates to an XML external entity expansion (XXE) in Solr config files (solrconfig.xml, schema.xml, managed-schema). In addition, Xinclude functionality provided in these config files is also affected in a similar way. The vulnerability can be used as XXE using file/ftp/http protocols in order to read arbitrary local files from the Solr server or the internal network. Users are advised to upgrade to either Solr 6.6.4 or Solr 7.3.1 releases both of which address the vulnerability. Once upgrade is complete, no other steps are required. Those releases only allow external entities and Xincludes that refer to local files / zookeeper resources below the Solr instance directory (using Solr's ResourceLoader); usage of absolute URLs is denied. Keep in mind, that external entities and XInclude are explicitly supported to better structure config files in large installations. Before Solr 6 this was no problem, as config files were not accessible through the APIs.
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Analysis
by VulDB Data Team • 02/07/2020
Apache Solr versions 6.0.0 through 6.6.3 and 7.0.0 through 7.3.0 contain a critical XML external entity expansion vulnerability that allows remote attackers to read arbitrary local files from the server through malformed configuration files. This vulnerability specifically affects solrconfig.xml, schema.xml, and managed-schema files where XML external entity processing is enabled. The flaw stems from insufficient validation of external entity references and XInclude functionality within these configuration files, creating a pathway for attackers to exploit the system using file, ftp, and http protocols to access sensitive data stored on the Solr server or within the internal network. The vulnerability represents a direct violation of the principle of least privilege as it allows unauthorized access to local resources that should remain protected within the server environment. This issue aligns with CWE-611, which describes improper restriction of XML external entity reference, and can be leveraged as part of broader attack vectors documented in the MITRE ATT&CK framework under initial access and privilege escalation techniques. The security implications extend beyond simple information disclosure as attackers can potentially map internal network structures, access configuration files containing sensitive information, and gather intelligence about the server environment. The vulnerability was addressed in Solr releases 6.6.4 and 7.3.1 through strict enforcement of resource access controls that limit external entity and XInclude references to only those within the Solr instance directory. These patched versions utilize Solr's ResourceLoader to validate and restrict access paths, explicitly denying absolute URLs and preventing access to arbitrary file locations. The mitigation strategy requires immediate upgrade to the patched versions as no additional configuration changes are necessary once the upgrade is complete. Before these versions, configuration files were not exposed through APIs, making this vulnerability particularly concerning as it introduced a new attack surface where previously protected configuration files became accessible to remote attackers. Organizations should ensure that all Solr instances are updated to prevent potential exploitation of this XXE vulnerability that could lead to data breaches and further compromise of internal systems. The fix implements a security-by-design approach that maintains the legitimate functionality of external entities and XInclude while preventing unauthorized access to local resources through proper path validation and access control mechanisms.