Office Outlook: Remote code execution via heap-based buffer overflow
Summary
Microsoft Office Outlook contains a heap-based buffer overflow that allows an unauthorized attacker to execute code over a network. The attack requires a user to interact, for example by opening a specially crafted file or message, as described by a third-party source. Outlook runs with the rights of the logged-in user, so a successful exploit gives access to that user's mailbox and cached credentials.
Affected
- Microsoft 365 Apps for Enterprise builds that predate the October 2026 Outlook update (version range listed by the CNA as 16.0.1 up to the Microsoft release page, not verified)
- Microsoft Office LTSC 2024 builds before 16.0.17932.21056 (per the CNA record, not verified against Microsoft)
- Outlook 2016, Outlook 2019 and Outlook 2021: no security updates were provided; whether they are affected by this CVE is not stated in the sources.
Fixed in
- October 13, 2026 Outlook security update for Microsoft 365 Apps and Office LTSC.
- The exact fixed build per channel is not confirmed by the sources; check the MSRC page and the Office release notes.
Workaround
Unknown. No workaround or mitigation specific to this CVE was found. Patching is the fix.
Exploitation
- Not publicly disclosed according to Microsoft.
- Not listed in the CISA KEV catalog.
- CISA SSVC data: exploitation none, automatable no.
- No public proof of concept found; this is not proof that none exists.
- EPSS score: unknown.
Our recommendation
- Confirm the installed Office build per channel against the MSRC page and the Microsoft Office release notes, and install the October 2026 Outlook update.
- Inventory all Outlook 2016, 2019 and 2021 installations and plan migration, because these versions did not receive the October update.
- Keep gateway attachment filtering and phishing protection active as defence in depth.
- Train users to be cautious with unexpected emails and attachments.
Information from Microsoft (Patch Tuesday October 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Response Center: CVE-2026-70256 msrc.microsoft.com
- Microsoft Office release notes: Microsoft 365 Apps security updates learn.microsoft.com
- OpenCVE: CVE-2026-70256 app.opencve.io
- Vulners: NVD CVE-2026-70256 vulners.com
- Robert365: Latest updates for classic Outlook (blog, not a Microsoft source) robert365.com
- DEV Community: Microsoft October 2026 updates (third-party, unverified) dev.to
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 31 Oct 2026, 18:48.
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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