Microsoft Office Outlook: Remote code execution via stack-based buffer overflow
Summary
A stack-based buffer overflow in Microsoft Office Outlook allows an unauthorized remote attacker to execute code on the affected system. The CVSS vector requires no privileges but user interaction (UI:R), so an attacker needs a user to take an action such as opening a crafted item; the exact trigger is not stated in the sources. Successful exploitation would give full confidentiality, integrity and availability impact on the user's system.
Affected
- Microsoft 365 Apps for Enterprise (32-bit and x64): 16.0.1 before the fixed build listed at https://aka.ms/OfficeSecurityReleases (fixed build number unknown)
- Microsoft Office LTSC 2021 (32-bit and x64): 16.0.1 before 16.0.14334.21048
- Microsoft Office LTSC 2024 (32-bit and x64): 16.0.0 before 16.0.17932.21140
- Office 2019, Office 2016 and other channels: Unknown.
Fixed in
- Microsoft 365 Apps for Enterprise: Unknown (check the MSRC advisory and https://aka.ms/OfficeSecurityReleases)
- Microsoft Office LTSC 2021: 16.0.14334.21048 or later
- Microsoft Office LTSC 2024: 16.0.17932.21140 or later
Workaround
Unknown. No vendor workaround was found in the sources reviewed.
Exploitation
- No evidence of exploitation in the wild was found; not listed in CISA KEV according to a third-party tracker.
- CVSS exploit code maturity is 'unproven'.
- No public proof of concept was found; the CVE was published today.
Our recommendation
- Identify all Outlook, Microsoft 365 and Office LTSC installations and their build numbers.
- Apply the update from the MSRC advisory once confirmed and check builds against the listed thresholds.
- Until patched, instruct users not to open unexpected attachments or links and enable email filtering and attachment controls.
- Monitor for CISA KEV listing and vendor updates.
Information from Microsoft (Patch Tuesday November 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- MSRC Security Update Guide: CVE-2026-123381 msrc.microsoft.com
- CVE Record CVE-2026-123381 www.cve.org
- Strix: CVE-2026-123381 www.strix.ai
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 10 Nov 2026, 21:13.
Original description (NVD)
Stack-based buffer overflow in Microsoft Office Outlook allows an unauthorized attacker to execute code over a network.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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