CVE-2013-1915 in ModSecurity
Summary
by MITRE
ModSecurity before 2.7.3 allows remote attackers to read arbitrary files, send HTTP requests to intranet servers, or cause a denial of service (CPU and memory consumption) via an XML external entity declaration in conjunction with an entity reference, aka an XML External Entity (XXE) vulnerability.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 05/06/2021
The CVE-2013-1915 vulnerability represents a critical XML External Entity processing flaw in ModSecurity versions prior to 2.7.3, which fundamentally undermines the security posture of web application firewalls designed to protect against XML-based attacks. This vulnerability stems from insufficient validation of XML content within the ModSecurity rule engine, creating a pathway for remote attackers to exploit the system through malformed XML data that contains external entity declarations. The flaw operates at the core of XML parsing mechanisms where the system fails to properly restrict access to external resources during XML document processing, enabling attackers to manipulate the parsing behavior in ways that were never intended by the security framework's designers.
The technical exploitation of this vulnerability occurs when ModSecurity encounters XML data containing external entity declarations that reference external resources, either through file system access or network connections. Attackers can construct malicious XML payloads that, when processed by the vulnerable ModSecurity instance, trigger unintended behavior where the system attempts to resolve external entities from local files or internal network resources. This creates three distinct attack vectors within a single vulnerability: unauthorized file access allowing attackers to read sensitive files on the server, the ability to send HTTP requests to internal network services bypassing normal network segmentation, and the potential to consume excessive CPU and memory resources through recursive entity references causing denial of service conditions. The vulnerability specifically leverages the XML parsing behavior where entity references are expanded during document processing without proper restrictions on external resource access.
The operational impact of CVE-2013-1915 extends beyond simple data exposure, as it fundamentally compromises the integrity and availability of the ModSecurity protection framework itself. When exploited, this vulnerability allows attackers to bypass the very security controls that ModSecurity is designed to enforce, potentially enabling further attacks against the underlying web applications or infrastructure. The ability to read arbitrary files creates opportunities for information disclosure attacks that could expose sensitive configuration data, authentication credentials, or application source code. The intranet server access capability represents a significant escalation, allowing attackers to probe internal network services that should normally be protected from external access, effectively breaking down network segmentation boundaries. The denial of service component creates additional operational concerns as attackers can consume system resources and potentially cause legitimate service interruptions that affect business operations.
Security mitigations for CVE-2013-1915 primarily focus on upgrading to ModSecurity version 2.7.3 or later, where the XML parsing validation has been enhanced to properly restrict external entity access. Organizations should implement comprehensive XML validation policies that explicitly disable external entity processing in all XML parsers within their security infrastructure. The remediation process requires careful consideration of existing security rules that may depend on XML processing capabilities, necessitating thorough testing to ensure that the security controls remain effective after implementing the patch. Additionally, organizations should consider implementing additional monitoring and logging around XML processing activities to detect potential exploitation attempts. From a broader security perspective, this vulnerability aligns with CWE-611, which specifically addresses improper restriction of XML external entity reference, and maps to ATT&CK technique T1213.002 for data from information repositories, demonstrating how XML processing flaws can enable information gathering and lateral movement within compromised environments. The vulnerability underscores the importance of maintaining up-to-date security software and implementing defense-in-depth strategies that do not rely solely on a single security control for protection against complex attack vectors.