CVE-2026-76181 in LibreOffice
Summary
by MITRE • 11/05/2026
LibreOffice includes a dBASE database driver, which reads dBASE tables and their .ndx index files when a folder of dBASE files is used as a data source. A heap buffer overflow existed when an index page was read. The number of entries recorded in a page was not checked against the number of entries the page could hold, which comes from a different field of the index header. A crafted index could also make a page refer back to itself, so that reading it recursed without end. In fixed versions the index header and the entry count of each page are limited to what an index page can hold, and a page that refers back to one of its parent pages is not followed.
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Analysis
by VulDB Data Team • 11/05/2026
The vulnerability identified in LibreOffice involves a critical heap buffer overflow within the dBASE database driver component, specifically affecting the processing of .ndx index files associated with dBASE tables. This security flaw arises from insufficient validation during the parsing and reading of index page structures. When a folder containing dBASE files is utilized as a data source, the application attempts to read both the table data and its corresponding index files to facilitate efficient record retrieval. The core technical deficiency lies in the lack of boundary checks when interpreting the metadata within these index pages. Specifically, the number of entries recorded within an individual page was not validated against the maximum capacity defined by the index header structure. This discrepancy allows a maliciously crafted .ndx file to specify entry counts that exceed the allocated memory buffer size for that specific page.
The exploitation of this heap buffer overflow can lead to arbitrary code execution or application crashes, depending on how the overwritten memory is utilized and what data resides in adjacent memory regions. By supplying an index header with manipulated values, an attacker can force the application to write beyond the bounds of the allocated heap memory. This type of vulnerability falls under CWE-122, which describes a heap-based buffer overflow where input validation failures allow for out-of-bounds writes that compromise memory integrity and confidentiality. The impact is severe because it affects the stability and security of the office suite whenever such files are opened or processed as data sources, potentially allowing remote code execution if an attacker can trick a user into opening a specially crafted document linked to these malicious index files.
Furthermore, the vulnerability description highlights a secondary logic flaw involving infinite recursion through self-referential page pointers within the index structure. A crafted index file could be designed so that a specific page entry points back to itself or one of its parent pages in the tree hierarchy. When the driver attempts to traverse this structure to resolve record locations, it enters an endless loop without end. This recursive behavior leads to stack exhaustion and subsequent denial of service conditions. While primarily causing instability, such deep recursion can also be leveraged in conjunction with memory corruption techniques to escalate privileges or crash the application more reliably. This aspect aligns with CWE-674 regarding uncontrolled recursion, which contributes to resource consumption and system unavailability.
The remediation strategy implemented in fixed versions of LibreOffice addresses both the buffer overflow and the recursive traversal issues through strict input validation and structural constraints. The developers introduced limits on the index header fields and enforced checks that ensure the number of entries per page does not exceed what an index page can physically hold. This prevents the heap buffer overflow by ensuring memory allocations match actual data requirements. Additionally, the fix implements logic to detect when a page refers back to one of its parent pages in the hierarchy. By refusing to follow such self-referential or cyclic pointers, the application avoids infinite recursion and stabilizes the parsing process against malformed index structures.
From an operational perspective, this vulnerability underscores the risks associated with integrating legacy database formats into modern office applications without rigorous security auditing. The dBASE format is relatively old, and its file structures may not account for modern memory safety practices unless explicitly handled by developers. Users should ensure they are running updated versions of LibreOffice to mitigate these risks. Administrators deploying this software in enterprise environments should verify patch levels across all endpoints. Furthermore, defense-in-depth measures such as sandboxing office applications can limit the impact if a user inadvertently opens a malicious file containing crafted dBASE index files.
In terms of threat intelligence and attack classification, this vulnerability is relevant to ATT&CK technique T1203, which covers exploitation for client-side execution via compromised software or documents. Although it requires specific data source configurations, the ability to crash or execute code through standard document interactions makes it a significant concern for social engineering attacks targeting office productivity suites. Security teams should monitor for indicators of compromise related to unusual memory access patterns in LibreOffice processes and ensure that all third-party drivers integrated into the application suite are kept up to date with security patches provided by upstream vendors.