CVE-2026-21520Public exploitNetwork attack vector

Data exfiltration via unsanitized form prompt

Published Jan 22, 2026 · Updated Jan 22, 2026

Indirect prompt injection in Microsoft Copilot Studio allows remote attackers to read sensitive data through a crafted SharePoint form submission. Copilot Studio concatenates the form's untrusted Comments value with agent system instructions, allowing injected text to override the intended prompt. The agent must process a public form and have access to connected SharePoint Lists and an external-email action; the demonstrated consequence is data exfiltration.

CVSS severity7.5
High
EPSS probability1.46%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Indirect prompt injection in Microsoft Copilot Studio allows remote attackers to read sensitive data through a crafted SharePoint form submission. Copilot Studio concatenates the form's untrusted Comments value with agent system instructions, allowing injected text to override the intended prompt. The agent must process a public form and have access to connected SharePoint Lists and an external-email action; the demonstrated consequence is data exfiltration.

The record

CVE
CVE-2026-21520
Published
Jan 22, 2026
Updated
Jan 22, 2026
Vendor
Microsoft
Product
Microsoft Copilot Studio
Classifications
CWE-77, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 22, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=-

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft Copilot Studioversion=-

Published CVSS scores

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

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-77Improper Neutralization of Special Elements used in a Command ('Command Injection')
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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