CVE-2026-123377: Microsoft Office Outlook heap-based buffer overflow

CVE-2026-123377 · Severity: high · CVSS 8.8 · Published 2026-11-10

Microsoft Office Outlook, an email and calendar application used across enterprises, contains a heap-based buffer overflow vulnerability. An attacker on the network can exploit this flaw to execute arbitrary code on an affected system without authentication, potentially leading to data theft, system compromise, or malware installation.

Technologies: Microsoft Outlook. Vendors: Microsoft.

Quick answers

Is CVE-2026-123377 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-123377 being exploited in the wild.
How severe is CVE-2026-123377?
High severity, with a CVSS score of 8.8, published 10 November 2026.
Which products and versions are affected?
Microsoft Outlook.
Is there a fix for CVE-2026-123377?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-123377 attacked?
It is attacked over the network.
Am I affected by CVE-2026-123377?
Check whether you run Microsoft Outlook. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A heap-based buffer overflow in Microsoft Office Outlook allows remote code execution via network attack vector without requiring user authentication or interaction. The vulnerability enables an attacker to overwrite heap memory and execute arbitrary code in the context of the Outlook process.

Affected products

  • Microsoft Outlook

Timeline

  • 2026-11-10: disclosed

References

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