CVE-2019-9847 in LibreOffice
Summary
by MITRE
A vulnerability in LibreOffice hyperlink processing allows an attacker to construct documents containing hyperlinks pointing to the location of an executable on the target users file system. If the hyperlink is activated by the victim the executable target is unconditionally launched. Under Windows and macOS when processing a hyperlink target explicitly activated by the user there was no judgment made on whether the target was an executable file, so such executable targets were launched unconditionally. This issue affects: All LibreOffice Windows and macOS versions prior to 6.1.6; LibreOffice Windows and macOS versions in the 6.2 series prior to 6.2.3.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 06/08/2020
This vulnerability resides in the hyperlink processing functionality of LibreOffice, a widely used office suite that processes documents across multiple operating systems. The flaw represents a critical security oversight in how the software handles user-initiated hyperlinks, specifically failing to implement proper validation checks on executable file targets. The vulnerability is particularly concerning because it operates at the user interaction level where trust is implicitly placed in the document content, creating a scenario where legitimate document features become attack vectors.
The technical implementation flaw occurs when LibreOffice processes hyperlinks that point to local file system locations on Windows and macOS platforms. The software's hyperlink handler lacks the necessary security checks that would normally prevent execution of potentially malicious executable files. This absence of validation means that when a user clicks on a hyperlink within a document, the system automatically executes whatever file path is specified in the hyperlink without performing any analysis of the target file type or extension. The vulnerability affects all versions prior to 6.1.6 and 6.2.3, indicating this was a persistent issue across multiple release series.
The operational impact of this vulnerability is significant as it enables attackers to craft malicious documents that appear legitimate while containing hidden executable payloads. When victims open these documents and activate hyperlinks, either through direct clicking or by following the document's intended workflow, the system executes the specified executable without user confirmation or security warnings. This behavior aligns with attack patterns described in the attack tree framework where user interaction is leveraged to bypass traditional security controls. The vulnerability effectively removes the user's ability to make informed decisions about file execution, creating an automatic execution path that can be exploited for malware delivery.
From a cybersecurity perspective, this vulnerability demonstrates a failure in the principle of least privilege and proper input validation, which are fundamental concepts in secure coding practices. The issue can be mapped to CWE-78, which addresses improper neutralization of special elements used in OS commands, and also relates to CWE-79, concerning cross-site scripting vulnerabilities, though in a local file system context. The attack surface is particularly broad as it affects both Windows and macOS platforms, making it relevant to a wide range of users. Organizations should implement immediate mitigations including updating to affected LibreOffice versions, implementing application control policies, and educating users about the risks of opening documents from untrusted sources.
The vulnerability highlights the importance of secure hyperlink processing in office applications and demonstrates how seemingly benign features can become security risks when proper validation is omitted. This issue underscores the necessity of comprehensive security testing that includes user interaction scenarios and proper handling of file system operations. The affected versions represent a window of opportunity for attackers to exploit this vulnerability, making timely patching essential for maintaining system integrity. Security teams should monitor for indicators of compromise related to this vulnerability and ensure that their endpoint protection solutions are configured to detect and prevent unauthorized executable launches from document hyperlinks.