A critical vulnerability in Microsoft Outlook has emerged that allows attackers to gain complete control of computers through a simple email preview, requiring no user interaction beyond the automatic display of messages in the Preview Pane. The security flaw, designated CVE-2025-30377, exploits a use-after-free memory corruption issue that facilitates arbitrary code execution when Outlook automatically renders malicious emails or attachments.
The vulnerability affects Microsoft 365 Apps across all builds prior to May 2025 security updates, including Office versions 2016 through 2024. Office Online Server versions 2019-2025 and standalone Outlook installations from 2019-2025 remain vulnerable until patched, with both desktop and certain web versions impacted depending on backend patch deployment status.
Technical analysis reveals the flaw stems from improper memory management within Outlook’s rendering engine, particularly involving uninitialized pointer handling and use-after-free conditions. Attackers manipulate email headers, particularly Content-Length parameters, or embed oversized file elements to trigger memory corruption.
Attackers exploit memory corruption vulnerabilities by manipulating email headers and oversized file elements to trigger rendering engine flaws.
This corruption grants control flow hijacking, redirecting program execution to attacker-supplied shellcode that bypasses Outlook’s Protected View security mechanisms. Attack vectors include malformed MIME attachments, malicious calendar invites, and crafted RTF documents delivered through phishing campaigns.
The zero-click nature of exploits like CVE-2025-21298 means buffer overreads and pointer dereferencing occur automatically during message preview, without requiring users to open attachments or click suspicious links. CVE-2025-30377 stands out as one of most dangerous vulnerabilities discovered this year due to its minimal attack requirements and widespread impact. Credential harvesting operations increasingly exploit these preview pane vulnerabilities to compromise user accounts at scale. This vulnerability particularly threatens over 400 million enterprise users who rely on Outlook for daily communications and calendar management.
Successful exploitation grants attackers the ability to remotely execute code, install malware, harvest sensitive data, and establish persistent system access with the permissions of the logged-in Outlook user. Compromised endpoints frequently serve as initial footholds for lateral movement within enterprise networks, bypassing traditional security awareness training focused on attachment-based threats.
Microsoft addressed these vulnerabilities through critical patches released in May 2025, implementing improved memory boundary validation and object model hardening.
Organizations with delayed patch cycles remain particularly vulnerable to large-scale phishing campaigns that exploit the minimal user interaction requirements, emphasizing the urgent need for immediate security updates across all Outlook installations.
