CVE-2019-9850 in LibreOffice
Summary
by MITRE
LibreOffice is typically bundled with LibreLogo, a programmable turtle vector graphics script, which can execute arbitrary python commands contained with the document it is launched from. LibreOffice also has a feature where documents can specify that pre-installed scripts can be executed on various document script events such as mouse-over, etc. Protection was added, to address CVE-2019-9848, to block calling LibreLogo from script event handers. However an insufficient url validation vulnerability in LibreOffice allowed malicious to bypass that protection and again trigger calling LibreLogo from script event handlers. This issue affects: Document Foundation LibreOffice versions prior to 6.2.6.
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Analysis
by VulDB Data Team • 11/21/2025
The vulnerability described in CVE-2019-9850 represents a critical security flaw in LibreOffice that stems from inadequate input validation mechanisms within the document scripting system. This issue specifically targets the LibreLogo component, which serves as a programmable turtle graphics scripting environment that can execute arbitrary Python commands directly from within document files. The vulnerability emerges from the complex interaction between LibreOffice's document event handling system and its security measures designed to prevent unauthorized script execution. When documents contain embedded scripts that are intended to execute automatically during various user interactions such as mouse-over events, the system's protection mechanisms become crucial for maintaining security boundaries. The flaw demonstrates how security controls can be circumvented through insufficient validation of input parameters, creating a pathway for malicious actors to bypass intended safeguards.
The technical exploitation of this vulnerability relies on a specific validation flaw in the URL handling mechanism within LibreOffice's scripting environment. This vulnerability allows attackers to craft malicious documents that can bypass the protection mechanisms implemented to address CVE-2019-9848, which was designed to prevent LibreLogo from being invoked through script event handlers. The insufficient URL validation means that when documents specify script execution triggers, the system fails to properly verify the legitimacy of the script invocation paths, enabling attackers to construct URLs or script references that appear benign but actually trigger the execution of LibreLogo functionality. This bypass mechanism operates at the core of LibreOffice's document security model, where the distinction between safe and unsafe script execution is determined by URL validation routines that are fundamentally flawed. The vulnerability specifically affects versions prior to 6.2.6, indicating that the fix required a complete reevaluation of how URL validation is performed within the document scripting subsystem.
The operational impact of CVE-2019-9850 extends beyond simple remote code execution capabilities, as it represents a complete breakdown in the document security model that could enable attackers to perform sophisticated attacks. When a user opens a malicious document, the system's attempt to execute pre-installed scripts in response to user interactions becomes a vector for arbitrary code execution, potentially allowing attackers to install malware, exfiltrate data, or compromise the entire system. The vulnerability's exploitation requires minimal user interaction beyond opening the malicious document, making it particularly dangerous in phishing campaigns or targeted attacks. From an attack perspective, this vulnerability aligns with ATT&CK technique T1059.006 for Python execution and T1204.002 for user execution, as it leverages document-based attack vectors that can be delivered through email attachments or web downloads. The flaw also relates to CWE-20, which addresses improper input validation, and CWE-78, which covers OS command injection vulnerabilities, as the system's failure to properly validate URLs creates opportunities for command injection attacks.
Organizations and users affected by this vulnerability face significant risk due to the prevalence of LibreOffice in enterprise environments and the ease with which malicious documents can be distributed. The vulnerability's impact is particularly severe because it operates within the context of trusted document opening operations, making it difficult for users to recognize the threat. Security mitigations should focus on immediate version updates to LibreOffice 6.2.6 or later, which contain the necessary URL validation fixes. Additionally, organizations should implement document scanning policies that can identify potentially malicious LibreOffice documents and restrict automatic script execution in enterprise environments. The vulnerability highlights the importance of proper input validation and the need for comprehensive security testing of document processing systems, particularly those that support scripting capabilities. From a defensive standpoint, this vulnerability underscores the necessity of maintaining up-to-date software versions and implementing layered security approaches that can detect and prevent exploitation attempts even when primary protections are bypassed. The fix for this vulnerability required substantial changes to the URL parsing and validation logic within LibreOffice's scripting engine, demonstrating the complexity of securing document processing applications against sophisticated attack vectors that exploit seemingly simple validation flaws.