CVE-2021-20873Network attack vector

Information exposure and alteration via unrestricted custom URLs

Published Dec 28, 2021 · Updated Aug 3, 2024

Missing authorization in Yappli 7.3.6 through versions before 9.30.0 allows remote attackers to redirect Android apps via custom URLs. The custom URL scheme handler accepts a crafted URL without adequately restricting access to its URL-opening function, causing the app to connect to an unintended site. A user must visit a malicious website and activate the URL; the redirect can expose or alter information held inside the app.

CVSS severity5.5
Medium
EPSS probability0.84%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Missing authorization in Yappli 7.3.6 through versions before 9.30.0 allows remote attackers to redirect Android apps via custom URLs. The custom URL scheme handler accepts a crafted URL without adequately restricting access to its URL-opening function, causing the app to connect to an unintended site. A user must visit a malicious website and activate the URL; the redirect can expose or alter information held inside the app.

The record

CVE
CVE-2021-20873
Published
Dec 28, 2021
Updated
Aug 3, 2024
Vendor
Yappli, Inc.
Product
Yappli
Classifications
CWE-862, CWE-939, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 28, 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 since v7.3.6 and prior to v9.30.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Yappli, Inc. · Yappliversion=versions since v7.3.6 and prior to v9.30.0

Published CVSS scores

5.5JPCERT/CCCVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
8.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
4.3JPCERT/CCAV:N/AC:M/Au:N/C:N/I:P/A:N
5.8NIST NVDAV: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 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-862Missing Authorization
CWE-939Improper Authorization in Handler for Custom URL Scheme
T1204.001Malicious Link

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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