CVE-2026-56096 in Apache Solr Extension
Summary
by MITRE • 08/25/2026
The extension passes the user-supplied search query parameter to Apache Solr without restricting advanced Solr query syntax such as wildcards, field selectors and range queries. A remote, unauthenticated attacker can use this syntax to enumerate indexed field names and extract their stored values through boolean- and range-based blind extraction techniques, independent of any site-specific configuration.
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Analysis
by VulDB Data Team • 08/25/2026
The vulnerability described constitutes a critical information disclosure flaw within an extension that interfaces with Apache Solr, allowing remote unauthenticated attackers to perform data exfiltration without requiring valid credentials or specific site configurations. This issue stems from the failure to sanitize and restrict advanced query syntax provided by users in search parameters. By passing user-supplied input directly to the underlying search engine without adequate validation against complex operators such as wildcards, field selectors, and range queries, the application exposes its internal indexing structure to exploitation. The core technical flaw lies in the lack of input filtering mechanisms that would normally prevent clients from leveraging Solr's powerful query capabilities for unauthorized reconnaissance or data extraction purposes.
From a technical perspective, this vulnerability enables attackers to enumerate indexed field names through boolean-based blind extraction techniques. By crafting specific queries that return different responses based on whether certain fields exist or contain specific values, an attacker can systematically deduce the schema of the database behind Solr. This process does not rely on error messages or direct output but rather on analyzing response times or status codes to infer structural information about the indexed data. Once field names are identified, range-based blind extraction techniques allow for the retrieval of stored values within those fields. Attackers can iteratively narrow down character sets and positions in string values by querying ranges such as greater than or less than specific ASCII values, effectively reconstructing sensitive data piece by piece without triggering traditional intrusion detection systems that look for obvious injection patterns.
The operational impact of this vulnerability is severe, particularly for applications handling sensitive personal information, financial records, or proprietary business data stored within Solr indexes. Since the attack requires no authentication and operates independently of site-specific configurations such as access control lists or permission settings, it represents a significant risk to any deployment using this extension in an internet-facing environment. The ability to extract arbitrary field values means that attackers can potentially compromise user privacy by leaking passwords, email addresses, identification numbers, or other personally identifiable information. Furthermore, the enumeration of schema details provides valuable intelligence for subsequent attacks, such as targeted SQL injection if Solr is connected to a relational database backend, or privilege escalation attempts based on discovered administrative fields.
This vulnerability aligns with CWE-209, which covers the generation of error messages containing sensitive information, although in this case it extends further into CWE-1058, involving the exposure of data through improper query construction. In terms of offensive security frameworks, this behavior maps to ATT&CK technique T1608, specifically Stage 1: Drive-by Compromise or Data Staging via Search Engine Queries, and more broadly falls under reconnaissance activities where attackers gather information about target systems before launching further exploits. The use of boolean-based blind extraction is a sophisticated method often associated with advanced persistent threats seeking to avoid detection while extracting high-value data from hardened environments.
Mitigation strategies must focus on strict input validation and the principle of least privilege regarding query capabilities. Developers should implement allow-listing for search parameters, ensuring that only expected characters and simple operators are permitted in user-supplied queries. Advanced Solr features such as wildcards (*), field selectors (field:value), and range queries ([start TO end]) should be disabled or heavily restricted unless explicitly required by the application's core functionality and protected by additional authentication layers. Implementing rate limiting on search endpoints can also help mitigate brute-force style extraction attempts by slowing down the iterative process of blind data retrieval. Additionally, deploying a Web Application Firewall with rules tuned to detect anomalous query patterns involving complex Solr syntax can provide an external layer of defense against exploitation attempts that bypass application-level controls.