Microsoft Office Excel: Information disclosure through buffer over-read
Summary
A buffer over-read in Microsoft Office Excel allows an unauthorized attacker to read memory beyond the end of a buffer and disclose information over a network. Exploitation requires a user to open a crafted file, for example one received by email or download. The vulnerability is limited to confidentiality, and the attacker does not need an account on the victim's system.
Affected
- Microsoft 365 Apps for Enterprise (32-bit and x64), from 16.0.1 before the build listed in Microsoft's security release page
- Office 365 for Mac, from 1.0.0 before 16.115.26110837
- Office LTSC 2021 (32-bit and x64), from 16.0.1 before 16.0.14334.21048
- Office LTSC 2024 and Office LTSC for Mac 2021/2024: listed only by a secondary source, not verified against Microsoft
Fixed in
- Office 365 for Mac: 16.115.26110837
- Office LTSC 2021: 16.0.14334.21048
- Microsoft 365 Apps for Enterprise: Unknown (fixed build not stated in the CNA record; see Microsoft's advisory)
- Patch released with the November 2026 Office security updates
Workaround
- No workaround is documented, because a patch is available.
- Until the update is installed, avoid opening untrusted spreadsheets from email or downloads (general practice, not a documented workaround).
Exploitation
- No evidence of in-the-wild exploitation was found; CISA SSVC lists exploitation as none.
- Not listed in CISA KEV according to Strix.
- No public proof of concept found; public disclosure status is unconfirmed.
- Microsoft's own exploitability assessment is unknown.
Our recommendation
- Install the November 2026 Office security updates on all Microsoft 365 Apps, Office LTSC 2021 and Office for Mac clients, and confirm they are at or above the fixed builds.
- Verify LTSC 2024 and LTSC for Mac versions against Microsoft's advisory.
- Remind users not to open unexpected spreadsheets from email or downloads until patched.
- Priority: medium. Handle the exploited Outlook flaw in the same update cycle first, as it is likely more urgent.
Information from Microsoft (Patch Tuesday November 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-124183 msrc.microsoft.com
- CVE Record: CVE-2026-124183 www.cve.org
- Microsoft 365 Apps security updates learn.microsoft.com
- ZDI November 2026 Security Update Review www.thezdi.com
- Strix: CVE-2026-124183 www.strix.ai
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 11 Nov 2026, 12:01.
Original description (NVD)
Buffer over-read in Microsoft Office Excel allows an unauthorized attacker to disclose information 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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