CVE-2026-21520

HighRCE

Published: 22 January 2026

Published

22 January 2026

Modified

02 February 2026

KEV Added

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Patch

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CVSS Score 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS Score 0.0009 25.5th percentile

Risk Priority 15 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-21520 is a high-severity Command Injection (CWE-77) vulnerability in Microsoft Copilot Studio. Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 25.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

This vulnerability is AI-related — categorised as Enterprise AI Assistants.

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190) and 1 other technique.

Threat & Defense Details

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

T1059 Command and Scripting Interpreter Execution

Adversaries may abuse command and script interpreters to execute commands, scripts, or binaries.

attack.mitre.org →

Why these techniques?

Remote unauthenticated network exploitation of public-facing Copilot Studio service via command injection (CWE-77) directly enables initial access and arbitrary command execution.

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

NVD Description

Exposure of Sensitive Information to an Unauthorized Actor in Copilot Studio allows a unauthenticated attacker to view sensitive information through network attack vector

Deeper analysisAI

CVE-2026-21520 is a vulnerability in Microsoft Copilot Studio that results in the exposure of sensitive information to an unauthorized actor. It allows an unauthenticated attacker to view sensitive data through a network-based attack vector. The issue has a CVSS v3.1 base score of 7.5, rated as High severity, with the vector AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N, and is associated with CWE-77 (Command Injection). The vulnerability was published on 2026-01-22.

An unauthenticated attacker (PR:N) can exploit this vulnerability remotely over the network (AV:N) with low complexity (AC:L) and without requiring user interaction (UI:N). Successful exploitation enables the attacker to obtain high-impact confidentiality disclosures (C:H) of sensitive information, with no impact on integrity or availability.

Mitigation details are available in the official advisory from the Microsoft Security Response Center at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21520.

Details

CWE(s): CWE-77

Affected Products

microsoft

copilot studio

all versions

AI Security AnalysisAI

AI Category: Enterprise AI Assistants
Risk Domain: N/A
OWASP Top 10 for LLMs 2025: None mapped
Classification Reason: Matched keywords: copilot

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References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21520
Vendor Advisory · secure@microsoft.com