SB2026021092 - Multiple vulnerabilities in Microsoft Excel

Description

This security bulletin contains information about 3 vulnerabilities.

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

CWE-ID: CWE-122 - Heap-based Buffer Overflow

CVSSv4: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber

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)

CWE-ID: CWE-125 - Out-of-bounds read

CVSSv4: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:U/U:Green

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)

CWE-ID: CWE-125 - Out-of-bounds read

CVSSv4: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:U/U:Green

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