Microsoft Office Outlook: Heap-based buffer overflow enables remote code execution
Summary
Microsoft Office Outlook contains a heap-based buffer overflow (CWE-122) that allows an unauthenticated remote attacker to execute code. According to the CVSS vector, no privileges are needed but a user must interact, for example by opening or previewing a crafted message. The exact trigger is not documented in the sources reviewed. NVD analysis was still pending at publication, and the CVSS score is 8.8.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the fixed build (exact build unknown)
- Office LTSC 2021: 16.0.1 to below 16.0.14334.21048
- Office LTSC 2024: 16.0.0 to below 16.0.17932.21140
Note: version data comes from the CVE record and a third-party aggregator and has not yet been verified against MSRC.
Fixed in
- Microsoft 365 Apps for Enterprise: Unknown. Check the Microsoft 365 Apps update history.
- Office LTSC 2021: 16.0.14334.21048 (per aggregator, unverified)
- Office LTSC 2024: 16.0.17932.21140 (per aggregator, unverified)
Workaround
Unknown. No workaround is documented; the security update is the only confirmed remedy.
Exploitation
- Exploited in the wild: not known for this CVE.
- Not listed in CISA KEV according to a third-party aggregator; not authoritatively checked.
- Public proof of concept: none found.
Our recommendation
- Install the November 2026 security updates for Microsoft 365 Apps and Office LTSC 2021/2024 once the MSRC advisory confirms the builds.
- Prioritise internet-facing systems and clients that handle mail from external senders.
- Restrict the Reading Pane and automatic previews as a general hardening step (own recommendation, not a documented mitigation).
- Keep all Outlook builds current, as Outlook heap overflows were also patched in October 2026.
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-2026-123383 msrc.microsoft.com
- CVE Record: CVE-2026-123383 www.cve.org
- strix.ai: CVE-2026-123383 (third-party, unverified) www.strix.ai
- Trinetriops: November 2026 Patch Tuesday trinetriops.com
- BleepingComputer: November 2026 Patch Tuesday www.bleepingcomputer.com
- Vulners: October 2026 Outlook update check 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 10 Nov 2026, 21:14.
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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