CVE-2026-78519 in 365 Apps for Enterprise
Summary
by MITRE • 09/09/2026
Use of uninitialized resource in Microsoft Office Outlook allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability described involves the improper initialization of resources within Microsoft Office Outlook, specifically creating conditions that allow for remote code execution when processing maliciously crafted content. This class of flaw typically manifests as a use-of-uninitialized-variable or uninitialized-memory error, where the application fails to properly set initial values for memory locations before they are accessed or utilized in subsequent operations. In the context of network-based attacks, this often occurs during the parsing and rendering of email messages, calendar items, or other data structures received from external sources. When Outlook processes these inputs, it may allocate memory buffers without zeroing them out or assigning default values, leaving residual data from previous allocations present in those memory regions.
An unauthorized attacker can exploit this flaw by crafting a specially designed message that triggers the specific code path where uninitialized resources are accessed. By carefully controlling the input payload, the attacker can manipulate how Outlook interprets these uninitialized memory segments. This manipulation allows for arbitrary control over program execution flow or data integrity checks within the application process. Since Microsoft Office Outlook is frequently used to receive emails from untrusted sources such as internet-based mail servers, this vulnerability presents a significant attack surface. The ability to execute code remotely means that an attacker does not need physical access to the target machine nor do they require user interaction beyond opening or previewing the malicious message in many scenarios.
The operational impact of successfully exploiting this vulnerability is severe, resulting in full compromise of the affected system under the context of the logged-in user. If a standard user account is used, an attacker may gain limited privileges to install programs, view, change, or delete data, and create new accounts with basic user-level rights. However, if the victim is operating with administrative privileges, such as domain administrator status, the impact escalates dramatically. The attacker would then have complete control over the affected system, enabling them to install programs, modify any registry settings, access confidential files, and potentially pivot to other systems on the network. This capability effectively bypasses standard security boundaries because the malicious code runs with the same privileges as the legitimate application process.
From a classification perspective, this vulnerability aligns closely with CWE-457, which defines Use of Uninitialized Variable, indicating that the software relies on memory content without ensuring it has been properly initialized beforehand. Furthermore, in terms of tactical behavior within an attack lifecycle, this exploitation technique corresponds to ATT&CK T1203, specifically referencing Exploitation for Client Execution. This categorization highlights how attackers leverage vulnerabilities in client-side applications like email clients to establish a foothold on target networks without requiring complex social engineering beyond the delivery of the malicious artifact itself.
Mitigation strategies primarily involve applying vendor-provided security updates that address the underlying memory management flaws within Outlook's codebase. Organizations should ensure that all systems running Microsoft Office are patched with the latest cumulative updates released by Microsoft to close these gaps in resource initialization logic. Additionally, implementing strict email filtering policies and deploying anti-malware solutions capable of inspecting message content for known exploit patterns can provide an additional layer of defense. Users should also be educated on the risks associated with opening unexpected attachments or viewing untrusted emails, although technical controls remain the most effective countermeasure against automated exploitation attempts targeting this specific vulnerability class.