Description

Integer overflow or wraparound in Microsoft Office Outlook allows an unauthorized attacker to execute code over a network.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.8",
  "pubDate": "2026-08-11T17:19:10.777Z",
  "pubdate": "2026-08-11T17:19:10.777Z",
  "executiveSummary": "An integer overflow or wraparound vulnerability exists within Microsoft Office Outlook, presenting significant security risks to enterprise environments and end-user workstations. This memory corruption flaw allows an unauthorized, remote attacker to achieve arbitrary code execution over a network without requiring prior authentication or user interaction beyond standard data processing.\nThe vulnerability stems from improper arithmetic validation during the parsing of specific data structures within Microsoft Office Outlook. When an attacker supplies maliciously crafted input designed to induce an integer overflow or wraparound condition, memory allocation calculations fail to accurately reflect the required buffer size. This discrepancy typically leads to heap-based or stack-based buffer overflows.\nSuccessful exploitation of this flaw grants the attacker the execution privileges of the currently logged-on user, potentially enabling complete system compromise, unauthorized data exfiltration, lateral movement within the network, and the installation of persistent backdoors or secondary payloads.\nGiven that Microsoft Office Outlook processes untrusted network data such as emails, calendar invites, and attachments automatically or upon standard user review, the attack surface is broad. Risk mitigation relies heavily on applying official vendor patches as soon as they become available, restricting network exposure, and implementing defense-in-depth measures to limit process privileges and detect anomalous memory execution patterns.",
  "technicalDetails": "The vulnerability is classified as an integer overflow or wraparound condition residing within the data parsing and rendering engine of Microsoft Office Outlook. The root cause originates from insecure arithmetic operations performed when calculating buffer allocation sizes for incoming network data or file structures. Specifically, when the application computes the memory required to store parsed elements, the input values can be manipulated to exceed the maximum representable value of the integer data type, causing an arithmetic wrap-around.\nThis wraparound results in an allocation size that is significantly smaller than the actual data payload being processed. When the parsing routine subsequently copies the incoming stream into the undersized memory buffer, a classic buffer overflow occurs, overwriting adjacent heap or stack memory structures. Attackers craft specialized payloads delivered over network protocols, embedded within standard Outlook communication vectors, to trigger this parsing mechanism.\nThe attack flow proceeds as follows: First, the unauthorized remote attacker constructs a malicious payload designed to exploit the integer calculation flaw. Second, the payload is transmitted over the network to the target system running Microsoft Office Outlook. Third, Outlook receives the network traffic and initiates the parsing of the malicious structure through its internal components. Fourth, the vulnerable function evaluates the manipulated size fields, inducing an integer overflow during the memory allocation sizing phase. Fifth, the application allocates a truncated memory buffer based on the wrapped integer value. Sixth, during the subsequent copy or read operation, the routine writes out-of-bounds data into adjacent memory regions, corrupting critical control data or function pointers. Finally, the attacker achieves arbitrary code execution by redirecting execution flow to shellcode contained within the payload, operating under the security context of the user running Microsoft Office Outlook.\nThe affected component is integral to Microsoft Office Outlook's data processing pipeline. Exploitation requires network connectivity to the target environment or the delivery of malicious content processed by the application. The vulnerability requires no authentication and can be triggered remotely, making it critical for network defenders to monitor network perimeters and endpoint telemetry for anomalous process crashes, unexpected child process spawning from the Outlook executable, and memory tampering indicators."
}