CVE-2017-3163 in Solr
Summary
by MITRE
When using the Index Replication feature, Apache Solr nodes can pull index files from a master/leader node using an HTTP API which accepts a file name. However, Solr before 5.5.4 and 6.x before 6.4.1 did not validate the file name, hence it was possible to craft a special request involving path traversal, leaving any file readable to the Solr server process exposed. Solr servers protected and restricted by firewall rules and/or authentication would not be at risk since only trusted clients and users would gain direct HTTP access.
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Analysis
by VulDB Data Team • 12/27/2022
Apache Solr's Index Replication feature presents a critical path traversal vulnerability in versions prior to 5.5.4 and 6.x before 6.4.1, where the HTTP API endpoint accepting file names lacks proper input validation. This flaw resides in the replication mechanism that allows follower nodes to fetch index files from leader nodes, creating a potential attack vector through malformed file path requests. The vulnerability manifests when an attacker crafts a malicious HTTP request containing directory traversal sequences such as ../ or ..\ that bypass the intended file access restrictions. This weakness falls under CWE-22 Path Traversal and aligns with ATT&CK technique T1071.004 Application Layer Protocol: DNS, as the attack exploits legitimate application protocols while leveraging improper input handling.
The technical implementation of this vulnerability stems from insufficient sanitization of file name parameters within the replication API endpoint. When Solr processes requests to pull index files, it directly uses the provided file path without validating or normalizing the input against a safe whitelist of allowed paths. Attackers can exploit this by submitting crafted requests that include path traversal sequences, enabling them to access arbitrary files on the server filesystem that the Solr process has read permissions for. The impact extends beyond simple information disclosure, as attackers may potentially read configuration files, database credentials, or other sensitive data stored within the server's file system. This vulnerability represents a classic privilege escalation scenario where an authenticated user with access to the replication API can leverage the path traversal to gain unauthorized access to sensitive system resources.
The operational impact of CVE-2017-3163 varies significantly based on the deployment environment and security controls in place. In environments where Solr instances are directly exposed to untrusted networks without proper firewall restrictions or authentication mechanisms, the vulnerability presents a severe risk that could lead to complete system compromise. Even in protected environments, the vulnerability remains concerning as it could be exploited by attackers who gain access to the replication API through other attack vectors or by compromising legitimate users with sufficient privileges. The attack surface expands when considering that Solr installations often run with elevated privileges to access index files, making any successful exploitation potentially devastating. Organizations with proper network segmentation and access controls may mitigate the immediate risk, but the vulnerability still represents a design flaw that could be leveraged in combination with other attacks or in less secure deployment scenarios.
Mitigation strategies for this vulnerability should focus on immediate patching of affected Solr versions to 5.5.4 or 6.4.1 and later releases where the path traversal validation has been implemented. Organizations should also implement network-level controls such as firewall rules that restrict access to Solr's replication API endpoints to only trusted sources, ensuring that these endpoints are not exposed to untrusted networks. Additional defensive measures include implementing strong authentication and authorization controls for the replication API, monitoring for suspicious file access patterns, and conducting regular security assessments of Solr configurations. The vulnerability highlights the importance of input validation and the principle of least privilege in application security design, where API endpoints should never directly trust user-provided input without proper sanitization and validation processes. Security teams should also consider implementing intrusion detection systems that can identify and alert on suspicious path traversal patterns in HTTP requests to the Solr replication endpoints.