Microsoft Office Outlook: Remote code execution via stack-based buffer overflow
Summary
A stack-based buffer overflow in Microsoft Office Outlook allows an unauthenticated remote attacker to execute code on the affected system. The attack requires that a user performs an action, the exact trigger is not stated in the sources. The CVSS base score is 8.8 (High) with high impact on confidentiality, integrity and availability. NVD analysis was pending at the time of writing and no exploitation has been confirmed.
Affected
- Microsoft 365 Apps for Enterprise (32-bit and x64): 16.0.1 before the fixed build listed at aka.ms/OfficeSecurityReleases (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
- Mac builds: not listed in the CVE record
- New Outlook and Outlook on the web: unknown
Fixed in
- Microsoft Office LTSC 2021: 16.0.14334.21048
- Microsoft Office LTSC 2024: 16.0.17932.21140
- Microsoft 365 Apps for Enterprise: Unknown (see the Microsoft advisory)
Workaround
Unknown. No vendor-documented workaround was found.
Exploitation
- No public proof of concept or exploitation in the wild found at the time of writing.
- The CVSS vector contains E:U (exploit maturity Unproven).
- Not in CISA KEV as of now.
- Do not confuse with CVE-2026-124194, a separate Outlook flaw reported as exploited.
Our recommendation
- Install the Microsoft security update for Microsoft 365 Apps, Office LTSC 2021 and LTSC 2024 in the normal patch cycle, with higher priority due to the CVSS score.
- Confirm the fixed Microsoft 365 build in the MSRC advisory.
- Check the installed build numbers on all desktop Outlook clients.
- Remind users to be cautious with unexpected emails and attachments, and monitor for suspicious Outlook or Office activity.
Information from Microsoft (Patch Tuesday November 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-123375 msrc.microsoft.com
- CVE.org record CVE-2026-123375 www.cve.org
- Strix.ai mirror CVE-2026-123375 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, 21:16.
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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