Microsoft Excel heap-based overflow

Summaryinfo

A vulnerability, which was classified as critical, has been found in Microsoft Excel. This issue affects some unknown processing. This manipulation causes heap-based overflow. This vulnerability appears as CVE-2026-21259. The attack may be initiated remotely. There is no available exploit. To fix this issue, it is recommended to deploy a patch.

Detailsinfo

A vulnerability was found in Microsoft Excel (affected version unknown). It has been declared as critical. Affected by this vulnerability is an unknown functionality. The manipulation with an unknown input leads to a heap-based overflow vulnerability. The CWE definition for the vulnerability is CWE-122. A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc(). As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to elevate privileges locally.

The weakness was presented 02/10/2026 as confirmed security update guide (Website). It is possible to read the advisory at msrc.microsoft.com. This vulnerability is known as CVE-2026-21259. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. It demands that the victim is doing some kind of user interaction. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 02/14/2026).

The vulnerability scanner Nessus provides a plugin with the ID 298976 (Security Updates for Microsoft Excel Products C2R (February 2026)), which helps to determine the existence of the flaw in a target environment.

Applying a patch is able to eliminate this problem. A possible mitigation has been published immediately after the disclosure of the vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (298976). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Type

• Spreadsheet Software

Vendor

• Microsoft

Name

• Excel

License

• commercial

Website

• Vendor: https://www.microsoft.com/

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Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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