# CVE-2026-26824: libxls use of uninitialized memory in OLE container parser

Source: https://junglewise.ai/threats/cve-2026-26824-libxls-use-of-uninitialized-memory-in-ole-container-parser  
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-2026-26824 · Severity: info · CVSS 0 · 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 clear memory before using it when opening a specially crafted spreadsheet. This could allow an attacker to crash applications using the library or potentially gain access to sensitive information stored in the computer's memory.

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

## Quick answers

**Is CVE-2026-26824 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-26824 being exploited in the wild.

**How severe is CVE-2026-26824?** Informational severity, with a CVSS score of 0, published 3 June 2026.

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

**Is there a fix for CVE-2026-26824?** 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-2026-26824 attacked?** It is attacked over the network or with local access, in a software library.

**Am I affected by CVE-2026-26824?** 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 through version 1.6.3 within the OLE container parser. The root cause is located in the read_MSAT() function, where memory allocated for the Master Sector Allocation Table (MSAT) is not fully initialized before being passed to and consumed by ole2_validate_sector_chain(). An attacker can exploit this by providing a specially crafted XLS file to an application using libxls (e.g., via xls_open_buffer()). This results in undefined behavior, which can manifest as a denial-of-service (crash) or the disclosure of heap residue. The issue was identified using MemorySanitizer (MSan).

## Affected products

- libxls libxls through 1.6.3

## Timeline

- 2026-01-15: disclosed: Issue reported on GitHub by rmhowe425
- 2026-06-03: advisory: CVE published by NVD

## References

- [https://github.com/libxls/libxls/issues/155](https://github.com/libxls/libxls/issues/155)

## Related threats

- [libxls out-of-bounds read in xls_dumpSummary](https://junglewise.ai/threats/cve-2026-79592-libxls-out-of-bounds-read-in-xls-dumpsummary)
- [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 xls_parseWorkBook](https://junglewise.ai/threats/cve-2026-26825-libxls-use-of-uninitialized-memory-in-xls-parseworkbook)