CVE-2026-102858: Heap-Based Buffer Overflow Flaw in Microsoft Office 365 for Mac Scores 8.8 on CVSS
A newly published high vulnerability in Microsoft Office 365 for Mac carries a CVSS score of 8.8. Here is what is affected and how to respond.
Key points
- CVE-2026-102858 affects Microsoft Office 365 for Mac.
- CVSS 8.8 (High).
- No exploitation confirmed yet.
Microsoft Office 365 for Mac is affected by CVE-2026-102858, a heap-based buffer overflow that the National Vulnerability Database rates 8.8 out of 10.
At a glance
- CVE
- CVE-2026-102858
- Product
- Microsoft Office 365 for Mac
- CVSS
- 8.8 High
- Weakness
- heap-based buffer overflow
- Exploited
- No known exploitation
What is the vulnerability?
The NVD entry states: Heap-based buffer overflow in Microsoft Office OneNote allows an unauthorized attacker to execute code over a network.
Affected versions
| Vendor | Product | Versions |
|---|---|---|
| Microsoft | Microsoft Office 365 for Mac | before publication |
| Microsoft | Microsoft Office LTSC for Mac 2021 | before publication |
| Microsoft | Microsoft Office LTSC for Mac 2024 | before publication |
CVSS vector: 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.
Is it being exploited?
There is no public confirmation of exploitation at the time of publication. It does not appear in CISA's Known Exploited Vulnerabilities catalog. We will update this report if that changes.
What should you do?
- Identify whether the affected product and versions run in your environment.
- Apply the vendor update listed in the advisory as soon as it is available.
- Limit network exposure of the affected service until it is patched.
- Monitor the vendor advisory for updated guidance or exploitation reports.
What to do and how to stay safe: CVE-2026-102858
- Vulnerability severity scores ignore your specific architecture and context.
- Exploitability depends on network exposure and user behavior, not just code flaws.
- Prioritization requires continuous asset inventory and threat intelligence alignment.
Risk-based vulnerability management focuses your limited resources on the flaws that actually threaten your business. Start by mapping your critical assets and checking for active exploits to prioritize your backlog.
Step-by-step guide: Risk-Based Vulnerability Management: Prioritize Fixes by Actual Danger
General security guidance from the Threat Times newsroom. It is not confirmed advice from the organisations named in this story.
Frequently asked questions
What is CVE-2026-102858?
CVE-2026-102858 is a heap-based buffer overflow vulnerability in Microsoft Office 365 for Mac.
How severe is CVE-2026-102858?
It has a CVSS score of 8.8 High.
Is CVE-2026-102858 being exploited?
There is no public confirmation of exploitation at the time of publication.
