# CVE-2026-78520: Microsoft Office Outlook out-of-bounds read allows remote code execution

Source: https://junglewise.ai/threats/cve-2026-78520-microsoft-office-outlook-out-of-bounds-read-allows-remote-code  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-08. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-78520 · Severity: medium · CVSS 6.5 · Published 2026-09-08

Microsoft Office Outlook is an email and calendar application used by millions of professionals to manage communications and scheduling. An out-of-bounds read vulnerability allows an attacker to execute arbitrary code on a user's computer by sending a specially crafted message over the network, potentially leading to unauthorized access to sensitive business data and system compromise.

Technologies: [Microsoft Office Outlook](https://junglewise.ai/threats/technologies/office-outlook). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft).

## Quick answers

**Is CVE-2026-78520 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-78520 being exploited in the wild.

**How severe is CVE-2026-78520?** Medium severity, with a CVSS score of 6.5, published 8 September 2026.

**Which products and versions are affected?** Microsoft Office Outlook.

**Is there a fix for CVE-2026-78520?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-78520 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-78520?** Check whether you run Microsoft Office Outlook. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

This vulnerability is an out-of-bounds read in Microsoft Office Outlook that permits remote code execution (RCE). The flaw is triggered when processing specially crafted email messages received over the network, requiring no user authentication to the vulnerable component itself. An attacker can exploit this by sending a malicious email that, when processed by Outlook, causes memory to be read outside allocated bounds, enabling arbitrary code execution in the context of the affected user. Network reachability is the primary requirement; the vulnerability does not appear to require user interaction beyond receiving the email. Microsoft has issued a security update to address this vulnerability.

## Affected products

- Microsoft Office Outlook

## Timeline

- 2026-09-08: disclosed

## References

- [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-78520](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-78520)

## Related threats

- [Microsoft Office Outlook path traversal in pathname handling](https://junglewise.ai/threats/cve-2026-124228-improper-limitation-of-a-pathname-to-a-restricted-directory-path)
- [Microsoft Office Outlook use of uninitialized resource code execution](https://junglewise.ai/threats/cve-2026-124227-use-of-uninitialized-resource-in-microsoft-office-outlook-allows)
- [Microsoft Office Outlook user warning spoofing vulnerability](https://junglewise.ai/threats/cve-2026-124194-microsoft-office-outlook-missing-user-interaction-for)
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- [Microsoft Office Outlook untrusted pointer dereference](https://junglewise.ai/threats/cve-2026-123382-untrusted-pointer-dereference-in-microsoft-office-outlook-allows)