CVE-2026-63268 in LibreOffice
Summary
by MITRE • 10/05/2026
LibreOffice Calc can link a cell range to an external data source, and the link is saved in the document. A link of the sql type could name a folder of local text files as a database, so opening a document could read a local text file into the sheet. In fixed versions only the csv, html and xml data providers are restored when a document is loaded.
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Analysis
by VulDB Data Team • 10/05/2026
The vulnerability in LibreOffice Calc represents a significant security flaw related to how external data links are processed during document loading operations. Specifically, the application allows users to link cell ranges within a spreadsheet to an external data source, with these links being persisted directly inside the saved document file. This functionality is designed to facilitate dynamic updates of spreadsheet content based on changes in external datasets. However, the implementation contains a critical oversight regarding the validation and restriction of supported database types when such documents are opened by other users or processed automatically.
The core technical flaw lies in the handling of SQL-type links that reference local file systems rather than traditional remote databases. An attacker can craft a malicious document containing a link configured to treat a specific folder on the victim's local machine as an external database source. When this document is opened, LibreOffice Calc attempts to resolve the link by reading data from the specified location. Because the application does not sufficiently restrict which file formats or sources are accessible through these SQL-type links during the loading phase, it can inadvertently read arbitrary local text files and inject their contents into the spreadsheet cells. This behavior effectively bypasses standard security boundaries that typically prevent applications from silently accessing sensitive local resources without explicit user interaction for each data source.
The operational impact of this vulnerability is substantial, primarily centering on unauthorized information disclosure. By forcing LibreOffice to load a document with a maliciously configured SQL link pointing to sensitive directories such as home folders or system configuration paths, an attacker can cause the application to exfiltrate local text files into the visible spreadsheet area. This mechanism allows for the passive extraction of data from the victim's environment without requiring further interaction after the initial opening of the file. The risk is exacerbated in automated environments where documents are processed by scripts or viewed on shared systems, as the malicious content becomes part of the document structure itself, potentially affecting multiple users who open the same compromised file.
To mitigate this risk, developers have implemented a strict whitelist approach for data providers during document loading operations. In fixed versions of LibreOffice Calc, only CSV, HTML, and XML data providers are restored when a document is loaded. This restriction effectively neutralizes the attack vector by preventing the application from interpreting arbitrary SQL-type links that point to local file system folders as valid database sources. By limiting the supported external data formats to those that do not pose an immediate risk of unintended local file access during the loading process, the vulnerability is addressed at its root cause. Users are advised to update their LibreOffice installation immediately to ensure these security controls are active and to remain cautious when opening documents from untrusted sources, even if they appear benign.
This issue aligns with CWE-20 Improper Input Validation, as the application failed to adequately validate the nature of external data links before processing them. Furthermore, it relates to ATT&CK technique T1567 Exfiltration Over Web Services or potentially local exfiltration methods where sensitive information is moved from a restricted environment to an attacker-controlled location via document manipulation. The fix demonstrates the importance of enforcing strict allow-lists for file handlers and data sources in office productivity software to prevent unintended side effects during routine operations like opening files.