CVE-2021-27635 in NetWeaver AS for JAVA
Summary
by MITRE • 06/09/2021
SAP NetWeaver AS for JAVA, versions - 7.20, 7.30, 7.31, 7.40, 7.50, allows an attacker authenticated as an administrator to connect over a network and submit a specially crafted XML file in the application because of missing XML Validation, this vulnerability enables attacker to fully compromise confidentiality by allowing them to read any file on the filesystem or fully compromise availability by causing the system to crash. The attack cannot be used to change any data so that there is no compromise as to integrity.
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Analysis
by VulDB Data Team • 06/11/2021
SAP NetWeaver AS for JAVA versions 7.20, 7.30, 7.31, 7.40, and 7.50 contain a critical vulnerability that stems from insufficient XML validation mechanisms within the application's file processing capabilities. This vulnerability falls under the CWE-611 weakness category, which specifically addresses improper restriction of XML external entity processing, making it susceptible to various forms of XML-based attacks including but not limited to XML External Entity (XXE) attacks. The vulnerability exists in the application's handling of XML files submitted through network connections, particularly when authenticated as an administrator, creating a significant security risk that can be exploited by malicious actors with administrative privileges.
The technical flaw manifests when the application processes specially crafted XML files without proper validation of external entity references or document type definitions. This lack of input validation allows attackers to manipulate XML parsing behavior and potentially access local file system resources through XML external entity expansion. The vulnerability operates at the application layer where XML documents are parsed and processed, creating a direct pathway for information disclosure and denial of service attacks. The absence of proper XML schema validation and entity expansion restrictions means that crafted XML payloads can trigger unintended system behavior, including file read operations that bypass normal access controls and system resource exhaustion that leads to service disruption.
The operational impact of this vulnerability is severe as it enables full compromise of confidentiality and availability while maintaining the integrity of the system. Attackers with administrative credentials can leverage this vulnerability to read arbitrary files from the application server's file system, potentially accessing sensitive configuration files, database credentials, application code, or other confidential data. The availability compromise occurs through system crashes or resource exhaustion attacks that can render the application or entire system unusable. This vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under T1059 for command and scripting interpreter and T1068 for exploit for privilege escalation, as it allows attackers to escalate their privileges within the application environment to gain access to system resources beyond normal administrative boundaries.
The attack vector requires an authenticated administrative user to submit malicious XML files, which means that the vulnerability cannot be exploited by unauthenticated users. However, this requirement does not mitigate the severity as administrative accounts are typically more privileged and often have broader access rights within the system. The vulnerability is particularly dangerous because it operates at the application processing level where XML files are parsed and interpreted, making it difficult to detect through traditional network-based security controls. Organizations should implement comprehensive input validation controls, disable external entity processing in XML parsers, and regularly update their SAP NetWeaver installations to address this vulnerability. The security controls should include monitoring for unusual XML processing activities and implementing proper access controls to limit administrative privileges to only necessary personnel. Additionally, the vulnerability demonstrates the importance of proper XML security configurations and highlights the need for organizations to conduct regular security assessments of their application frameworks to identify similar input validation weaknesses.