CVE-2026-21521Network attack vector

Information disclosure via unneutralized control sequences

Published Jan 22, 2026 · Updated Jan 22, 2026

Information disclosure in Microsoft 365 Copilot in Word allows remote attackers to read sensitive data via crafted control sequences. Microsoft identifies the locus only as Copilot and has not disclosed which input path mishandles the sequences or how data is exposed. Exploitation requires user interaction and an eligible Copilot experience, and the reported consequence excludes data modification and service interruption.

CVSS severity7.4
High
EPSS probability0.53%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Microsoft 365 Copilot in Word allows remote attackers to read sensitive data via crafted control sequences. Microsoft identifies the locus only as Copilot and has not disclosed which input path mishandles the sequences or how data is exposed. Exploitation requires user interaction and an eligible Copilot experience, and the reported consequence excludes data modification and service interruption.

The record

CVE
CVE-2026-21521
Published
Jan 22, 2026
Updated
Jan 22, 2026
Vendor
Microsoft
Product
Microsoft 365 Copilot in Word
Classifications
CWE-150
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 365 Copilot in Wordversion=-

Published CVSS scores

7.4Microsoft CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/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 exploitUnconfirmed

Weakness, pattern, technique

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

Public exploit references

No public exploit references are available in this record.

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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