Threat Intelligence / CVE / CVE-2026-78505

CVE-2026-78505 — Microsoft 365 Apps for Enterprise

CVSS v3.1 8.8 (HIGH) · Priority 4.4/10 · Published 2026-09-08

As of 2026-09-09, CVE-2026-78505 is a HIGH-severity vulnerability in Microsoft 365 Apps for Enterprise, CVSS v3.1 8.8. Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-78505, most recently “Microsoft September 2026 Patch Tuesday — 999 CVEs, 3 actively exploited zero-days (CVE-2026-85880, CVE-2026-81963, CVE-2026-85046)”.

Last updated: 2026-09-09

What is CVE-2026-78505?

Heap-based buffer overflow in Microsoft Office allows an unauthorized attacker to execute code over a network.

The record classifies CVE-2026-78505 under weakness class CWE-122. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs a user to take an action first, and has high impact on confidentiality, integrity, availability. 8 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 5 days ago.

Severity and exploitation probability

CVSS v3.1 base score: 8.8 — HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
CISA KEV: Not listed in the CISA Known Exploited Vulnerabilities catalog
Threadlinqs priority: 4.4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
Published: 2026-09-08, last modified 2026-09-09

Is CVE-2026-78505 being exploited?

No public exploitation evidence for CVE-2026-78505 is recorded in the sources Threadlinqs tracks — CISA KEV, Exploit-DB, public proof-of-concept repositories and ProjectDiscovery Nuclei — as of 2026-09-09. That is an absence of evidence in those feeds, not a guarantee that the vulnerability is unexploited.

Affected products and versions

Microsoft: 365 Apps for Enterprise, Office 2016, Office 2019, Office 365 for Mac, Office LTSC 2021, Office LTSC 2024, Office LTSC for Mac 2021, Office LTSC for Mac 2024

How to fix CVE-2026-78505

No vendor patch reference has been recorded for CVE-2026-78505 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

Threat activity tracking CVE-2026-78505

1 tracked threat in the Threadlinqs corpus references CVE-2026-78505, either in the campaign’s CVE list or as an indicator on the campaign record.

Microsoft September 2026 Patch Tuesday — 999 CVEs, 3 actively exploited zero-days (CVE-2026-85880, CVE-2026-81963, CVE-2026-85046) — CRITICAL · 2026-09-08

Sources

Enriched from CVE.org, GitHub Security Advisories. Last verified by Threadlinqs on 2026-09-09.

Vendor advisory and patch

msrc.microsoft.com — vendor advisory

Full detection coverage & IOCs for threats exploiting CVE-2026-78505 are available via the Threadlinqs MCP server (Purple tier). View plans →

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