SB2026021092 - Multiple vulnerabilities in Microsoft Excel

Description

This security bulletin contains information about 3 secuirty vulnerabilities.

1) Heap-based buffer overflow (CVE-ID: CVE-2026-21259)

The vulnerability allows a remote attacker to escalate privileges on the target system.

The vulnerability exists due to a boundary error in Microsoft Excel. A remote attacker can pass specially crafted data to the application, trigger a heap-based buffer overflow and gain elevated privileges on the system.

2) Out-of-bounds read (CVE-ID: CVE-2026-21261)

The vulnerability allows a remote attacker to gain access to potentially sensitive information.

The vulnerability exists due to a boundary condition in Microsoft Excel. A remote attacker can create a specially crafted Office file, trick the victim into opening it, trigger an out-of-bounds read error and read contents of memory on the system.

3) Out-of-bounds read (CVE-ID: CVE-2026-21258)

The vulnerability allows a remote attacker to gain access to potentially sensitive information.

The vulnerability exists due to a boundary condition in Microsoft Excel. A remote attacker can create a specially crafted Office file, trick the victim into opening it, trigger an out-of-bounds read error and read contents of memory on the system.

Remediation

Install update from vendor's website.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21259
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21261
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21258