CVE-2021-20733Network attack vector

Phishing redirection via unrestricted custom URL handler

Published Jun 22, 2021 · Updated Aug 3, 2024

Improper authorization in asken Inc. あすけんダイエット 3.0.0 through 4.2.x allows remote attackers to open arbitrary sites through its URL handler. The custom URL scheme handler passes a requested URL to the app's website-access function without restricting the destination. A user must interact with attacker-controlled content, after which the app displays the chosen site and exposes the user to phishing.

CVSS severity4.3
Medium
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

Improper authorization in asken Inc. あすけんダイエット 3.0.0 through 4.2.x allows remote attackers to open arbitrary sites through its URL handler. The custom URL scheme handler passes a requested URL to the app's website-access function without restricting the destination. A user must interact with attacker-controlled content, after which the app displays the chosen site and exposes the user to phishing.

The record

CVE
CVE-2021-20733
Published
Jun 22, 2021
Updated
Aug 3, 2024
Vendor
asken Inc.
Product
あすけんダイエット
Classifications
CWE-939, CWE-862, T1660
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 22, 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=versions from v.3.0.0 to v.4.2.x

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

asken Inc. · あすけんダイエットversion=versions from v.3.0.0 to v.4.2.x

Published CVSS scores

4.3JPCERT/CCCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
6.1NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.3JPCERT/CCAV:N/AC:M/Au:N/C:N/I:P/A:N
5.8NIST National Vulnerability DatabaseAV:N/AC:M/Au:N/C:P/I:P/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-939Improper Authorization in Handler for Custom URL Scheme
CWE-862Missing Authorization
T1660Phishing

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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