CVE-2021-20753Network attack vector

Authenticated browser script execution via Scheduler

Published Aug 18, 2021 · Updated Aug 3, 2024

Cross-site scripting in Scheduler in Cybozu Garoon 4.0.0 through 5.0.2 allows remote authenticated users to inject arbitrary script. Cybozu and JPCERT/CC have not disclosed which Scheduler input lacks output encoding or how the injected content reaches a rendered page. Exploitation requires product access and a logged-in user to view the affected content, causing attacker-supplied script to run in that user's browser.

CVSS severity5.4
Medium
EPSS probability0.60%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Scheduler in Cybozu Garoon 4.0.0 through 5.0.2 allows remote authenticated users to inject arbitrary script. Cybozu and JPCERT/CC have not disclosed which Scheduler input lacks output encoding or how the injected content reaches a rendered page. Exploitation requires product access and a logged-in user to view the affected content, causing attacker-supplied script to run in that user's browser.

The record

CVE
CVE-2021-20753
Published
Aug 18, 2021
Updated
Aug 3, 2024
Vendor
Cybozu
Product
Garoon
Classifications
CWE-79, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 18, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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=4.0.0 to 5.0.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Cybozu · Garoonversion=4.0.0 to 5.0.2

Published CVSS scores

3.5JPCERT/CC and IPAAV:N/AC:M/Au:S/C:N/I:P/A:N
5.4JPCERT/CC and IPACVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

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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