CVE-2023-26435 in OX App Suite
Summary
by MITRE • 06/20/2023
It was possible to call filesystem and network references using the local LibreOffice instance using manipulated ODT documents. Attackers could discover restricted network topology and services as well as including local files with read permissions of the open-xchange system user. This was limited to specific file-types, like images. We have improved existing content filters and validators to avoid including any local resources. No publicly available exploits are known.
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Analysis
by VulDB Data Team • 07/16/2023
The vulnerability CVE-2023-26435 represents a significant information disclosure and privilege escalation risk within the LibreOffice document processing framework. This flaw emerged from insufficient validation of file references within manipulated ODT documents, allowing attackers to leverage the local LibreOffice instance to access system resources that should otherwise remain restricted. The vulnerability specifically targeted the handling of local file system references and network endpoints during document rendering processes, creating a pathway for unauthorized reconnaissance and data exfiltration. The security implications extend beyond simple information disclosure as they encompass potential privilege escalation scenarios where attackers could access files readable by the open-xchange system user account, thereby compromising the integrity of the underlying system infrastructure.
The technical exploitation of this vulnerability stems from inadequate content filtering mechanisms within LibreOffice's document parser. When processing maliciously crafted ODT documents, the application failed to properly validate external resource references, particularly those pointing to local file system paths or network endpoints. This validation failure allowed attackers to embed references to local image files or other resource types that would then be loaded by the LibreOffice instance during document rendering. The vulnerability's scope was limited to specific file types such as images, which suggests the flaw existed within the image handling subsystem rather than affecting all document elements. This limitation indicates a targeted validation gap that could be exploited through carefully crafted document structures to access local resources while maintaining a degree of operational stealth.
The operational impact of CVE-2023-26435 presents a multifaceted threat landscape for affected systems. Attackers could potentially discover network topology information by leveraging the local LibreOffice instance to probe available network services, effectively bypassing standard network security controls. Additionally, the ability to include local files with read permissions of the open-xchange system user creates a direct pathway for data exfiltration and system reconnaissance. This vulnerability particularly affects environments where LibreOffice processes are executed with elevated privileges or where document processing occurs in contexts that expose sensitive system resources. The lack of publicly available exploits suggests that while the vulnerability exists, its exploitation requires specific technical knowledge and targeting, though the potential impact remains significant for organizations relying on document processing systems.
Security mitigations for CVE-2023-26435 primarily involve implementing enhanced content filters and validators as mentioned in the advisory. The fix addresses the core validation issue by strengthening the document parser's ability to identify and reject suspicious local resource references before they can be processed. Organizations should ensure that all LibreOffice installations are updated to versions containing the patched validation mechanisms, while also implementing additional security controls such as network segmentation and privilege reduction for document processing services. The vulnerability aligns with CWE-20: Improper Input Validation, which specifically addresses inadequate validation of input data leading to security vulnerabilities. From an ATT&CK perspective, this vulnerability maps to techniques involving privilege escalation and reconnaissance through local system access, potentially enabling adversaries to move laterally within affected environments. The remediation approach emphasizes the importance of input validation and content filtering as core defensive measures against similar classes of vulnerabilities that could enable unauthorized system access through document processing workflows.