Exploited vulnerabilities / CVE-2026-21509
Confirmed exploited · exploited vulnerability · Microsoft OfficeCVE-2026-21509
Microsoft Office exploited vulnerability, confirmed exploited in the wild.
Microsoft Office contains a security feature bypass vulnerability in which reliance on untrusted inputs in a security decision in Microsoft Office could allow an unauthorized attacker to bypass a security feature locally. Some of the impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.
| CISA's name for it | Microsoft Office Security Feature Bypass Vulnerability |
|---|---|
| Vendor and product | Microsoft · Office |
| Type | exploited vulnerability · CWE-807 |
| Exploited | Confirmed by CISA listed 26 January 2026 |
| Likelihood | one of the most likely to be exploited of every vulnerability tracked |
| Deadline | 16 February 2026 · already passed |
| Used in ransomware | Not reported |
| Advisories | msrc.microsoft.com ↗ · nvd.nist.gov ↗ |
Three steps, in this order
Apply the vendor's fix or mitigation; CISA lists only vulnerabilities seen exploited.
If you cannot patch now, restrict network access to the affected product.
Check for signs of compromise since the date it was added to the list.
| CISA's required action | Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. |
|---|
Know before someone else finds it
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CVE-2026-21509 in short
Is CVE-2026-21509 being exploited?
Yes. CISA added CVE-2026-21509 to its Known Exploited Vulnerabilities catalogue on 26 January 2026, which it does only on evidence of exploitation in the wild.
What is the CISA deadline for CVE-2026-21509?
US federal agencies must remediate it by 16 February 2026. Everyone else should treat that date as the latest safe point to patch an internet-facing system.
How likely is CVE-2026-21509 to be exploited in the next 30 days?
FIRST's Exploit Prediction Scoring System gives it 71%, the 99th percentile of every CVE it scores.
How do I fix CVE-2026-21509?
Apply the vendor's fix or mitigation; CISA lists only vulnerabilities seen exploited. If you cannot patch now, restrict network access to the affected product. Check for signs of compromise since the date it was added to the list.
Other Microsoft vulnerabilities being exploited
| CVE | Product | Type | Listed |
|---|---|---|---|
| CVE-2026-124194 | Office | exploited vulnerability | 10 November 2026 |
| CVE-2026-96951 | Windows | command injection | 13 October 2026 |
| CVE-2026-65660 | SharePoint | exploited vulnerability | 25 September 2026 |
| CVE-2026-81963 | Windows | privilege escalation | 8 September 2026 |
| CVE-2026-85880 | Windows | privilege escalation | 8 September 2026 |
| CVE-2019-1068 | SQL Server | remote code execution | 26 August 2026 |
Sources: CISA Known Exploited Vulnerabilities catalogue (released 10 November 2026) and FIRST EPSS. Page compiled automatically by SAK T.L.M, the threat-intelligence tool of SAK T.E.C, on 13 November 2026.