CVE tracker / CVE-2026-78520
CVE-2026-78520
CVE-2026-78520 is the Microsoft Office Outlook Information Disclosure Vulnerability. Microsoft rates it Critical, CVSS 6.5. It is not in CISA's Known Exploited Vulnerabilities catalog. Published September 8, 2026.
Risk summary
MediumRemote Code Execution
6.5
CVSS v3 base
0.9%
EPSS: chance of exploitation in 30 days
Medium
Severity
Critical
Microsoft's rating
Less Likely
Microsoft: exploitation
No
In CISA KEV
Microsoft describes it: “Out-of-bounds read in Microsoft Office Outlook allows an unauthorized attacker to execute code over a network.”
How to fix it
Microsoft lists 13 affected products and the update that fixes each:
- KB5002923 · fixed build 16.0.5569.1000
Microsoft Word 2016 (64-bit edition), Microsoft Word 2016 (32-bit edition) - Release Notes · fixed build 16.0.17932.20976, 16.0.20326.20138, 16.113.26091433
Microsoft Office LTSC 2024 for 32-bit editions, Microsoft 365 Apps for Enterprise for 32-bit Systems, Microsoft Office 365 for Mac, Microsoft Office LTSC for Mac 2024, Microsoft Office LTSC 2024 for 64-bit editions, and 6 more
What Microsoft changed
- September 17, 2026: Microsoft is announcing the availability of the security updates for Microsoft Office for Mac. Customers running affected Mac software should install the update for their product to be protected from this vulnerability. Customers running other Microsoft Office software do not need to take any action. See the Release Notes for more information and download links.
- September 8, 2026: Information published.
Details
- Weakness
- CWE-125: Out-of-bounds Read
- Publicly disclosed (Microsoft)
- No
- Exploited (Microsoft)
- No
- Known exploited (CISA KEV)
- Not listed
- Published
- September 8, 2026
- Last revised
- September 17, 2026
Get told when this changes
Senserva Watch emails Microsoft security and patch alerts when something moves: a new exploitation report, a revised fix, a known issue. Free, one email address.
References
From Microsoft, CISA, NVD and FIRST data; the Microsoft details were read when this page was opened. Check the references above before you act.