Microsoft Office Outlook: Remote code execution via heap-based buffer overflow
Summary
A heap-based buffer overflow in Microsoft Office Outlook allows an unauthorized attacker to execute code over the network. Exploitation requires user interaction and has high attack complexity, so a victim would typically need to open or preview a crafted message. The impact is rated high for confidentiality, integrity and availability (CVSS 7.5).
Affected
- Microsoft 365 Apps for Enterprise: versions from 16.0.1 before the current build listed on the Microsoft Office security release page (build not stated in the CVE record)
- Microsoft Office LTSC 2021: versions from 16.0.1 before 16.0.14334.21048
- Microsoft Office LTSC 2024: versions from 16.0.0 before 16.0.17932.21140
- Outlook 2016 and Office 2019 are not listed in the CVE record; Microsoft has not confirmed their status.
Fixed in
- Microsoft Office LTSC 2021: 16.0.14334.21048
- Microsoft Office LTSC 2024: 16.0.17932.21140
- Microsoft 365 Apps for Enterprise: Unknown (check the MSRC advisory)
Workaround
Unknown.
Exploitation
- CISA SSVC assessment: exploitation none, automatable no, technical impact total.
- Public proof-of-concept code: nothing found.
- Exploited in the wild: nothing known.
- A third-party tracker lists the CVE as not in CISA's KEV catalog; this has not been verified against CISA.
Our recommendation
- Patch Microsoft Office LTSC 2021 to at least 16.0.14334.21048 and LTSC 2024 to at least 16.0.17932.21140.
- Check the Microsoft 365 Apps build against the MSRC advisory and install the current update.
- Confirm that automatic updates work on all endpoints with Outlook.
- Re-check the MSRC advisory and CISA once NVD analysis is complete.
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-2026-123379 msrc.microsoft.com
- CVE Record CVE-2026-123379 (CVE Program) www.cve.org
- Strix AI: CVE-2026-123379 www.strix.ai
- EUVD-2026-73716 (Vulners) vulners.com
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 11 Nov 2026, 05:17.
Original description (NVD)
Heap-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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