CVE-2021-20806Network attack vector

Phishing redirects via crafted URLs

Published Oct 13, 2021 · Updated Aug 3, 2024

Open redirect in Cybozu Remote Service 3.0.0 through 3.1.9 allows remote attackers to redirect users to arbitrary websites via crafted URLs. Cybozu has not published the affected request handler or how it accepts and uses an untrusted destination when forming the redirect. Exploitation requires a user to access a specially crafted URL, enabling phishing through a trusted service origin.

CVSS severity3.4
Low
EPSS probability0.82%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Open redirect in Cybozu Remote Service 3.0.0 through 3.1.9 allows remote attackers to redirect users to arbitrary websites via crafted URLs. Cybozu has not published the affected request handler or how it accepts and uses an untrusted destination when forming the redirect. Exploitation requires a user to access a specially crafted URL, enabling phishing through a trusted service origin.

The record

CVE
CVE-2021-20806
Published
Oct 13, 2021
Updated
Aug 3, 2024
Vendor
Cybozu
Product
Cybozu Remote Service
Classifications
CWE-601
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 13, 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=3.0.0 to 3.1.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Cybozu · Cybozu Remote Serviceversion=3.0.0 to 3.1.9

Published CVSS scores

2.6JPCERT/CC and IPAAV:N/AC:H/Au:N/C:N/I:P/A:N
3.4JPCERT/CC and IPACVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:C/C:N/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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-601URL Redirection to Untrusted Site ('Open Redirect')

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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