# CVE-2026-26825: libxls use-of-uninitialized memory in xls_parseWorkBook

Source: https://junglewise.ai/threats/cve-2026-26825-libxls-use-of-uninitialized-memory-in-xls-parseworkbook  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-03. Updated: 2026-06-03  
License: CC BY 4.0 with a link back

CVE-2026-26825 · Severity: info · Published 2026-06-03

libxls is a software library used to read and parse Excel (.xls) files. A vulnerability exists where the library fails to properly initialize memory when processing specially crafted or malformed files. This could lead to unpredictable program behavior, incorrect data processing, or the potential exposure of sensitive information from the system's memory.

Technologies: [Libxls](https://junglewise.ai/threats/technologies/libxls). Vendors: [Libxls](https://junglewise.ai/threats/vendors/libxls).

## Quick answers

**Is CVE-2026-26825 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-26825 being exploited in the wild.

**How severe is CVE-2026-26825?** Informational severity, published 3 June 2026.

**Which products and versions are affected?** Libxls 1.6.3.

**Is there a fix for CVE-2026-26825?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-26825 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-26825?** Check whether you run Libxls at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A use-of-uninitialized memory vulnerability exists in libxls 1.6.3 within the xls_parseWorkBook() function. The root cause is located in the OLE parsing layer (ole2_read), where buffers allocated via ole_malloc() are not explicitly zero-initialized and may not be fully populated during short reads or when processing malformed OLE streams. An attacker can exploit this by providing a crafted XLS file, causing the parser to use uninitialized heap memory for control or data flow logic. This can result in undefined behavior, logic errors, or potential information disclosure of heap contents. The flaw was identified using MemorySanitizer (MSAN) and affects non-instrumented builds.

## Affected products

- libxls libxls 1.6.3

## Timeline

- 2026-01-16: disclosed: Issue reported on GitHub by rmhowe425
- 2026-06-03: advisory: CVE-2026-26825 published by NVD

## References

- [https://github.com/libxls/libxls/issues/156](https://github.com/libxls/libxls/issues/156)

## Related threats

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- [libxls heap-buffer-overflow and use-after-free in xls_getCSS](https://junglewise.ai/threats/cve-2026-79591-libxls-heap-buffer-overflow-and-use-after-free-in-xls-getcss)
- [libxls use of uninitialized memory in OLE container parser](https://junglewise.ai/threats/cve-2026-26824-libxls-use-of-uninitialized-memory-in-ole-container-parser)