CVE-2021-20777Network attack vector

Arbitrary website navigation via unrestricted URL handler

Published Jul 7, 2021 · Updated Aug 3, 2024

Improper authorization in GU App for Android 4.8.0 through 5.0.2 allows remote attackers to direct users to arbitrary websites. The custom URL scheme handler launches the app and accepts an arbitrary destination without enforcing access restrictions. A user must open an attacker-supplied custom-scheme link; the resulting navigation can expose the user to a malicious site's social-engineering content.

CVSS severity4.3
Medium
EPSS probability0.87%
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 GU App for Android 4.8.0 through 5.0.2 allows remote attackers to direct users to arbitrary websites. The custom URL scheme handler launches the app and accepts an arbitrary destination without enforcing access restrictions. A user must open an attacker-supplied custom-scheme link; the resulting navigation can expose the user to a malicious site's social-engineering content.

The record

CVE
CVE-2021-20777
Published
Jul 7, 2021
Updated
Aug 3, 2024
Vendor
G.U. CO., LTD.
Product
GU App
Classifications
CWE-939, CWE-862
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 7, 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 4.8.0 to 5.0.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

G.U. CO., LTD. · GU Appversion=versions from 4.8.0 to 5.0.2

Published CVSS scores

4.3JPCERT/CCCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
4.3JPCERT/CCAV:N/AC:M/Au:N/C:N/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 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-939Improper Authorization in Handler for Custom URL Scheme
CWE-862Missing Authorization

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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