CVE-2026-79592 in libxls
Summary
by MITRE • 09/10/2026
An out-of-bounds read vulnerability exists in the xls_dumpSummary() function of libxls 1.6.3 due to insufficient validation of file-controlled OLE summary offsets.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 09/10/2026
The vulnerability identified as an out-of-bounds read within the xls_dumpSummary function of libxls version 1.6.3 represents a critical memory safety issue rooted in inadequate input validation mechanisms. This specific component is responsible for parsing and extracting metadata from Microsoft Excel files, which utilize the OLE2 Compound Document format to store data structures including summary information streams. The core technical flaw lies in the failure to rigorously validate file-controlled offsets before they are used as pointers or indices into memory buffers. When a maliciously crafted spreadsheet containing malformed OLE header fields is processed by this library, the application attempts to access memory locations that lie outside the bounds of the allocated buffer associated with the summary stream data.
From a technical perspective, this flaw allows an attacker to trigger a read operation beyond the end of a valid memory region. In C-based libraries like libxls, such out-of-bounds reads do not typically result in immediate code execution but rather lead to information disclosure or application instability. The specific impact depends on what data resides immediately after the allocated buffer in memory. If sensitive cryptographic keys, session tokens, or other confidential structures are located adjacent to this buffer, an attacker could potentially exfiltrate that data through the malformed read operation. Alternatively, if the out-of-bounds access lands in unmapped memory pages, it will cause a segmentation fault, leading to a denial of service condition where the application crashes unexpectedly during file processing operations such as opening or converting Excel files.
This vulnerability aligns with Common Weakness Enumeration category CWE-125, which defines Out-of-Bounds Read vulnerabilities occurring when software reads data past the end or before the beginning of the intended buffer. The lack of proper boundary checks on user-supplied input, specifically file-controlled offsets in this context, is a classic example of insufficient validation leading to memory corruption issues. Furthermore, from an offensive security perspective, this flaw can be leveraged within the ATT&CK framework under techniques related to Collection and Exfiltration over Alternative Protocols if the extracted data contains sensitive information, or under Denial of Service tactics if the primary goal is system disruption through application crashes.
Mitigation strategies for this vulnerability primarily involve updating libxls to a patched version where developers have implemented strict bounds checking on all offsets derived from OLE summary streams before they are utilized in memory access operations. For organizations unable to immediately update their dependencies, defensive coding practices such as implementing wrapper functions that validate offset values against the total size of the mapped file content can provide temporary protection. Additionally, deploying runtime application self-protection tools or using compilers with stack-smashing detection enabled may help mitigate the impact by detecting abnormal memory access patterns before they lead to severe consequences. Regular auditing of third-party library usage and ensuring that all external inputs are treated as untrusted until explicitly validated is essential for preventing similar vulnerabilities in future development cycles.