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And let the phishing begin! Microsoft is taking action against a zero-day exploit already exploited in Office-ServiceNow Under Attack: How an Email Can Open the Doors to Your Business-Shocking Discovery on Instagram: Private Posts Accessible Without Login!-Email Security Under Pressure: Phishing Kits to Double in 2025-How a simple Visual Studio Code file can become a backdoor for state-run hackers-And let the phishing begin! Microsoft is taking action against a zero-day exploit already exploited in Office-ServiceNow Under Attack: How an Email Can Open the Doors to Your Business-Shocking Discovery on Instagram: Private Posts Accessible Without Login!-Email Security Under Pressure: Phishing Kits to Double in 2025-How a simple Visual Studio Code file can become a backdoor for state-run hackers

CVE-2026-21509

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This is a free service offered by Red Hot Cyber to the community. It allows you to view, on a single page, information about a single CVE from the National Vulnerability Database (NVD) and the National Institute of Standards and Technology (NIST) of the United States of America, the Forum of Incident Response and Security Teams (FIRST) regarding the EPSS score and percentile, data from the KEV catalog of the Cybersecurity and Infrastructure Security Agency (CISA), as well as selected resources from Red Hot Cyber and other international sources.

National Vulnerability Database Information

Description: Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

CVSS Base Score: 7.8 (v3.1)

The **CVSS Base Score** is a score from **0 to 10** that represents the intrinsic severity of a vulnerability. A higher score indicates greater severity.

Value

0.02.55.07.510.0

Published on: 01/26/2026 18:16:38
Last modified: 01/27/2026 02:00:01
NIST: CVE source from the National Vulnerability Database (NVD)

CVSS Metrics Details

Base Severity: HIGH
Vector String: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Attack Vector: LOCAL
Attack Complexity: LOW
Privileges Required: NONE
User Interaction: REQUIRED
Scope: UNCHANGED
Confidentiality Impact: HIGH
Integrity Impact: HIGH
Availability Impact: HIGH

Common Weakness Enumeration (CWE)

Database CWE: v4.18

CWE-807: Reliance on Untrusted Inputs in a Security Decision ↗

The product uses a protection mechanism that relies on the existence or values of an input, but the input can be modified by an untrusted actor in a way that bypasses the protection mechanism.

Fonte: MITRE CWE

FIRST Information

EPSS Score: N/A

The **EPSS (Exploit Prediction Scoring System)** is a score from **0 to 1** that indicates the **probability** that a vulnerability will be exploited in the real world in the next 30 days. A higher value indicates a greater likelihood of exploitation.

EPSS Score not available for this CVE.

Percentile: N/A

The **Percentile** indicates how much higher this vulnerability's EPSS score is compared to all other vulnerabilities in the EPSS database. For example, a percentile of 0.90 (90%) means that 90% of vulnerabilities have an EPSS score equal to or lower than the current one.

Percentile not available for this CVE.

*Data updated as of: N/A

CISA Information (Known Exploited Vulnerabilities)

The **CISA KEV Catalog** lists vulnerabilities that have been **actively exploited in the real world**. If a CVE is present in this catalog, it indicates that the threat is immediate and mitigation should be a top priority.

CVE **CVE-2026-21509** **IS PRESENT** in the CISA KEV Catalog!

Vulnerability Name: Microsoft Office Security Feature Bypass Vulnerability
Short Description: 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.
Date Added to KEV: 01/26/2026
Vendor/Product: Microsoft / Office
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.
Due Date: 02/16/2026

Articles published on Red Hot Cyber

NVD References

Exploit PoC from GitHub

No results found on GitHub for this CVE.