Patch tracker / CVE reference / CVE-2026-21258

CVE-2026-21258

CVE-2026-21258 is a high severity Microsoft vulnerability with a CVSS score of 7.8. Microsoft has shipped the fix: deploy one of the 2 updates below from the Microsoft Update Catalog, and see where this CVE sits against the rest on the patch tracker.

High

High severity Microsoft vulnerability, CVSS 7.8. Fixed by 2 Microsoft security updates.

Senserva AI read on CVE-2026-21258Official patches for CVE-2026-21258Change historyAdmin questions

Risk summary

CVSS base
7.8
EPSS exploit probability
<1%
Severity
High

Senserva AI Opinion for CVE-2026-21258

This Excel information disclosure bug, affecting Office Online Server and Office 2019, carries a High 7.8 severity but the lowest EPSS score of any item in this batch at just 1 percent. A vulnerability reachable through a malicious spreadsheet is still worth closing given how commonly Excel files move between organizations, even though attackers do not currently appear to be prioritizing it. It has not been confirmed exploited or tied to ransomware.

Do this: Patch Office 2019 and Office Online Server in the regular update cycle; this one does not need to be expedited given its 1 percent EPSS score.

AI-generated from public data, 2026-07-07. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for CVE-2026-21258

Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.

Schedule normally
No exploitation observed: not in the CISA KEV catalog, EPSS under 1%.
Fixed by KB5002835 and 1 more (by build, listed below). Download from the Microsoft Update Catalog, or deploy via Windows Update, Intune, or WSUS.
Do this now: Deploy with your normal update cycle. This page refreshes daily; the verdict changes the day the data does.

Updated August 7, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.

Full tracking and change history for CVE-2026-21258

Published
2026-02-10
Last revised
2026-02-10
Changes tracked
1

Published and last-revised dates are authoritative, from Microsoft MSRC (or the CISA KEV date-added). Senserva additionally records day-to-day changes from 2026-07-07, refreshed several times a day; the change count reflects that forward-only tracking.

Exploitation and severity

Not in the CISA KEV catalog. EPSS exploit probability <1%. CVSS 7.8 (High).

This CVE is among the lower half of tracked Microsoft CVEs by EPSS exploit probability.

Official patch(es) for CVE-2026-21258

Moderate priority: schedule it in your normal patch cycle. In Intune or Defender, confirm whether the fixing updates KB5002835, KB5002837 are installed across the affected products. Senserva does this automatically across your tenant and flags every missing patch.

Apply the Microsoft security updates below to fix CVE-2026-21258. Each KB page carries the Microsoft Update Catalog download, Microsoft's known issues for the update, a copy-paste PowerShell check for whether it is installed, and the Senserva AI read.

KB5002835KB5002837

Affected products

Fixed by the same updates

If you are patching CVE-2026-21258, the same updates also fix these:

CVE-2026-21259CVE-2026-21261

Authoritative references

Official CVE record (cve.org)NVD detailMicrosoft MSRCFIRST.org EPSS

Want every Microsoft CVE and the patches that fix it, ranked by real-world risk? See the Microsoft Patch Tracker.

New to a term on this page? CVE, KB, KEV, CVSS, and EPSS are each explained once, on the Senserva security lexicon. Reference: Microsoft CVE and vulnerability management and the Microsoft patching guide.
Data notice: this page, the feeds, and the API are provided as is, for informational purposes only, without warranty of any kind. Senserva, LLC does not guarantee the accuracy, completeness, or timeliness of third-party data (MSRC, NVD, CISA KEV, EPSS) and accepts no liability for actions taken based on it; verify against the authoritative vendor advisory before acting. Built daily with Senserva Trustworthy AI. All use of this data is subject to the Senserva EULA.