Outlook RCE Vulnerability Exploits User Interaction

A critical vulnerability in Microsoft Outlook has been disclosed by the company as part of its August 2026 Patch Tuesday rollout. The flaw, tracked as CVE-2026-70329, allows attackers to execute malicious code remotely through an integer overflow or wraparound weakness in Microsoft Office Outlook.

The vulnerability carries a CVSS v3.1 base score of 8.8, placing it in the High severity band. It requires user interaction, meaning an attacker must craft a malicious Office file, likely disguised as an email attachment, and convince the recipient to open it.

Once opened, the integer overflow bug can be triggered to corrupt memory and hijack program execution, potentially giving the attacker full control over the affected system depending on the victim's privilege level. Microsoft's patch covers a wide range of its Office ecosystem, including Microsoft 365 Apps for Enterprise, Microsoft Office 2019, and standalone Microsoft Outlook 2016 releases.

Security teams are urged to prioritize deploying the August 2026 cumulative update across all Outlook and Office installations, particularly in environments still running Office 2016 or LTSC builds that don't receive automatic Click-to-Run updates. Given that exploitation hinges on tricking a user into opening a malicious file, reinforcing phishing awareness training and email attachment filtering will further reduce risk while patches are rolled out fleet-wide.