Microsoft Office Outlook: Remote code execution via heap-based buffer overflow
Summary
A heap-based buffer overflow in Microsoft Office Outlook allows an unauthenticated attacker to execute code remotely over the network, with a CVSS 3.1 base score of 9.8 (critical). Microsoft's exploitability data rates it as unproven, and it is not publicly disclosed or known to be exploited. Research notes indicate that a crafted email may be triggered in the Reading Pane without user interaction, but Microsoft has not confirmed this preview vector, so the attack conditions remain partly unverified.
Affected
- Microsoft 365 Apps for Enterprise (32- and 64-bit)
- Office 365 for Mac
- Office LTSC 2021 (32- and 64-bit)
- Office LTSC 2024 (32- and 64-bit)
- Office LTSC for Mac 2021 and 2024
- Exact affected version ranges: see the MSRC advisory
Fixed in
- Security updates released on 13 October 2026 for Microsoft 365 Apps, Office LTSC 2021 and 2024 and Office 365 for Mac; see the MSRC advisory for build numbers
- Office LTSC for Mac 2021 and 2024: update not yet available; Microsoft will release it as soon as possible
- Exact fixed build numbers: Unknown.
Workaround
- No vendor workaround known.
- Interim hardening (not confirmed by the vendor for this CVE): disable the Reading Pane/preview for untrusted mail where practical and keep mail filtering such as Microsoft Defender for Office 365 active.
Exploitation
- Publicly disclosed: No.
- Exploited in the wild: No.
- Microsoft exploit code maturity: Unproven.
- CISA KEV: not listed. CISA SSVC: exploitation none, automatable yes, technical impact total.
- EPSS: about 1.3 percent.
- No public proof of concept found at the time of research.
Our recommendation
- Install the October 2026 Office security updates on all Outlook clients now, including Microsoft 365 Apps and Office LTSC.
- Verify Mac LTSC systems and track Microsoft's follow-up release for LTSC for Mac 2021 and 2024.
- Check update status with Microsoft Update or a vulnerability scanner such as Nessus on all Outlook clients.
- Consider disabling the Reading Pane for untrusted mail until patched.
- Monitor for proof-of-concept exploits, as the status may change quickly.
Information from Microsoft (Patch Tuesday October 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- MSRC advisory msrc.microsoft.com
- MSRC advisory (English) msrc.microsoft.com
- CrowdStrike Patch Tuesday analysis October 2026 www.crowdstrike.com
- Hivepro Microsoft October 2026 Patch Tuesday www.hivepro.com
- Tenable Nessus check for Outlook C2R October 2026 vulners.com
- Vulners/NVD vulners.com
- OpenCVE app.opencve.io
- Robert 365 latest updates for classic Outlook robert365.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 30 Oct 2026, 18:42.
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.
Affected? We can help.
We check whether your systems are affected, install updates and close the gap – continuously with the System Health Checker if you wish.