Attack Chain

1. Attacker crafts a malicious Excel file designed to trigger the use-after-free vulnerability (CVE-2026-32189).
2. The attacker delivers the malicious Excel file to the victim via email or other means.
3. The victim opens the malicious Excel file using a vulnerable version of Microsoft Excel.
4. Excel attempts to access a memory location that has already been freed, triggering the use-after-free condition.
5. The attacker leverages the memory corruption to overwrite critical data structures in Excel’s memory space.
6. The attacker redirects program execution to attacker-controlled code within the Excel process.
7. The attacker executes arbitrary code with the privileges of the user running Excel.
8. The attacker can then install malware, steal sensitive data, or perform other malicious actions on the local system.

Impact

Successful exploitation of CVE-2026-32189 allows an attacker to execute arbitrary code on the victim’s machine. This can lead to a complete compromise of the system, including data theft, malware installation, and privilege escalation. The vulnerability poses a significant risk to organizations that rely on Microsoft Excel for daily operations, as a single compromised user can provide a foothold for further attacks within the network. While specific victim counts are unavailable, the widespread use of Microsoft Excel suggests a potentially large attack surface.

Recommendation

• Apply the security update released by Microsoft to patch CVE-2026-32189 immediately (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-32189).
• Deploy the provided Sigma rules to detect potential exploitation attempts based on suspicious process creation and file activity.
• Monitor process creation events for unusual child processes spawned by Excel.exe, using logsource category process_creation.
• Monitor file access events for Excel accessing unusual locations or creating suspicious files, using logsource category file_event.