CVE-2013-6408 in Solr
Summary
by MITRE
The DocumentAnalysisRequestHandler in Apache Solr before 4.3.1 does not properly use the EmptyEntityResolver, which allows remote attackers to have an unspecified impact via XML data containing an external entity declaration in conjunction with an entity reference, related to an XML External Entity (XXE) issue. NOTE: this vulnerability exists because of an incomplete fix for CVE-2013-6407.
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Analysis
by VulDB Data Team • 12/23/2024
The vulnerability identified as CVE-2013-6408 represents a critical XML External Entity (XXE) flaw in Apache Solr versions prior to 4.3.1, specifically within the DocumentAnalysisRequestHandler component. This issue stems from an inadequate implementation of the EmptyEntityResolver mechanism, which should have prevented unauthorized access to external resources during XML processing. The vulnerability manifests when Solr processes XML data containing external entity declarations combined with entity references, creating a pathway for malicious actors to exploit the system through improperly validated input handling.
The technical exploitation of this XXE vulnerability occurs through the manipulation of XML documents submitted to Solr's DocumentAnalysisRequestHandler, where the system fails to properly sanitize external entity references. When an attacker crafts XML data containing external entity declarations that reference remote resources, the incomplete EmptyEntityResolver implementation allows these references to be resolved, potentially enabling information disclosure, denial of service attacks, or even remote code execution depending on the underlying system configuration and network access. This flaw specifically impacts the XML parsing and processing capabilities of Solr's analysis functionality, where external entity resolution should be strictly controlled or disabled entirely.
The operational impact of CVE-2013-6408 extends beyond simple data exposure, as it can enable attackers to perform server-side request forgery attacks, access internal network resources, or extract sensitive data from the Solr server environment. The vulnerability's relationship to the incomplete fix for CVE-2013-6407 demonstrates a pattern of security regressions where attempts to address one XXE vulnerability inadvertently create new attack vectors. This particular flaw affects organizations using affected Solr versions in production environments, potentially exposing their search infrastructure to unauthorized access and data exfiltration attempts. The vulnerability's classification aligns with CWE-611 (Improper Restriction of XML External Entity Reference) and maps to ATT&CK technique T1213.002 (Data from Information Repositories) and T1071.004 (Application Layer Protocol: DNS).
Organizations should immediately upgrade to Apache Solr version 4.3.1 or later to address this vulnerability, as the patch implements proper XML entity resolution controls and strengthens the EmptyEntityResolver functionality. Additional mitigations include implementing proper input validation for all XML data entering the system, disabling external entity resolution entirely in XML parsers, and configuring network-level restrictions to prevent access to internal resources from the Solr server. Security teams should also conduct comprehensive assessments of their Solr deployments to ensure no other XXE vulnerabilities exist within their search infrastructure, particularly examining configurations that might allow external entity references or implement weak XML parsing controls that could enable similar attack vectors.