Microsoft Office Outlook: Heap-based buffer overflow (remote code execution)
Summary
A heap-based buffer overflow in Microsoft Office Outlook allows an unauthorized attacker to execute code over a network. The CVSS 3.1 base score is 8.8. The attacker needs no privileges, but a user must interact, for example by opening a crafted message or file; the exact trigger is unknown. NVD analysis is still pending.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the fixed build (upper bound unconfirmed; the vendor entry is malformed)
- Microsoft Office LTSC 2021: 16.0.1 to below 16.0.14334.21048
- Microsoft Office LTSC 2024: 16.0.0 to below 16.0.17932.21140
Fixed in
- Microsoft Office LTSC 2021: 16.0.14334.21048 or later (per third-party mirror, not verified against MSRC)
- Microsoft Office LTSC 2024: 16.0.17932.21140 or later (per third-party mirror, not verified against MSRC)
- Microsoft 365 Apps for Enterprise: Unknown.
Workaround
- Vendor workaround: Unknown.
- General mitigations (not from a source): disable the Preview Pane, block executable and archive attachments at the mail gateway, and limit who can receive external mail.
Exploitation
- No reports of exploitation in the wild or public proof of concept found at the time of writing.
- Not listed in CISA KEV according to a third-party mirror; not verified.
- Not to be confused with CVE-2026-124194, a different Outlook flaw.
Our recommendation
- Deploy the November 2026 Office security updates in the standard patch cycle.
- Confirm the fixed build for Microsoft 365 Apps with MSRC before reporting compliance.
- Enable mail filtering for executable and archive attachments and train users on phishing.
- Monitor CISA KEV and the MSRC Exploitation Detected flag, and escalate if exploitation is reported.
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-2026-123384 msrc.microsoft.com
- Strix.ai mirror: CVE-2026-123384 (unverified) www.strix.ai
- Cybersecurity News: Microsoft November 2026 Patch Tuesday cybersecuritynews.com
- BleepingComputer: Microsoft November 2026 Patch Tuesday www.bleepingcomputer.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 10 Nov 2026, 21:15.
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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