What is the CVSS score of CVE-2026-21521?

CVE-2026-21521 has a CVSS 3.1 base score of 7.4 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N. EPSS exploitation probability: 0.1%.

How to fix or mitigate CVE-2026-21521?

Within 24 hours: Inventory all Copilot deployments and identify data sensitivity levels of connected systems. Within 7 days: Implement network segmentation to isolate Copilot instances and restrict outbound communications; disable Copilot features if non-critical to operations. Within 30 days: Monitor for vendor patch release and establish expedited testing/deployment procedures; conduct audit of accessed data for potential exposure.

AI / ML CVE-2026-21521

HIGH

Improper Neutralization of Escape, Meta, or Control Sequences (CWE-150)

2026-01-22 secure@microsoft.com

Information Disclosure Microsoft AI / ML 365 Word Copilot

7.4

CVSS 3.1 · NVD

View

Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

Access

Craft malicious input with control sequences
Delivery

User clicks/interacts with crafted content
Exploit

Copilot fails to neutralize escape sequences
Execution

Information disclosure occurs
Impact

Attacker retrieves sensitive data

Vulnerability Assessment

Weakness	CWE CWE-150 OWASP Top 10:2025 A05:2025 - Injection ASVS 5.0 V1 - Encoding and Sanitization Escape character neutralization
Exploitation Conditions	User interaction required (UI:R). Target must be running vulnerable Copilot version. Attacker crafts input containing improperly neutralized escape or control sequences. No authentication required; remote exploitation possible via network vector.
Impact	CVSS 7.4 (HIGH). Attack vector: Network. Complexity: Low. Privileges required: None. User interaction: Required. Exploitation no authentication required. Exploitable via remote/network.
Exploit ScenarioDerived	A remote attacker without authentication could exploit this vulnerability to compromise the affected system.

This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).

Patch available 0.1% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 12, 2026

Information disclosure in Microsoft 365 Word Copilot enables unauthenticated attackers to extract sensitive data through improper handling of escape and control sequences in network communications. The vulnerability requires user interaction to trigger and affects the Copilot AI/ML service with a CVSS score of 7.4. No patch is currently available.

Earlier versions of this analysis (1)

v1 Mar 12, 2026 - 21:54 CVSS 7.4

Improper neutralization of escape, meta, or control sequences in Copilot allows an unauthorized attacker to disclose information over a network. [CVSS 7.4 HIGH]

RemediationAI

Monitor vendor advisories for a patch. Restrict network access to the affected service where possible.

Affected Packages

microsoft 365_word_copilot fix: Microsoft 365 Word Copilot

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in microsoft

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

Affects 365 Word Copilot. Improper neutralization of escape, meta, or control sequences in Copilot allows an unauthorized attacker to disclose information over a network.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 7.4 HIGH

AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Changed

Confidentiality

High

Integrity

None

Availability

None

DescriptionCVE.org

Improper neutralization of escape, meta, or control sequences in Copilot allows an unauthorized attacker to disclose information over a network.

Executive ViewAI

Why It Matters

CVE-2026-21521 is a high-severity vulnerability in Copilot that enables attackers to extract sensitive information through improper handling of control sequences. With no patch currently available, organizations using Copilot face immediate risk of data disclosure until vendor remediation is released.

Business Impact: High

Compensating Controls

Implement network segmentation isolating Copilot from sensitive data systems; restrict outbound network connectivity to approved endpoints only; disable Copilot functionality if business-critical operations do not depend on it; deploy WAF/proxy rules to monitor and block suspicious control sequences in Copilot traffic; enforce strict access controls limiting which users/services interact with Copilot; increase logging and monitoring for unusual data exfiltration patterns; consider temporary suspension of Copilot use for processing confidential or regulated data.

Threat Intelligence Overview

EPSS Score

0.1%

Top 80% exploitable

Data Quality

3 sources

Confidence: Low

NVD

CVE.org

EPSS

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity HIGH

CISA KEV No

Public POC No

EPSS 0.1%

Patch available Yes

Active threat No

Deciding rule

HIGH severity (CVSS 7.0-8.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Scheduled

Exploitation· derived

None

System Exposure· derived

Open

Automatable· derived

Human Impact

High

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +37

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.