CVE-2021-20873
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedYappli is an application development platform which provides the function to access a requested URL using Custom URL Scheme. When Android apps are developed with Yappli versions since v7.3.6 and prior to v9.30.0, they are vulnerable to improper authorization in Custom URL Scheme handler, and may be directed to unintended sites via a specially crafted URL.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceYappli Android apps versions v7.3.6 through v9.30.0 contain improper authorization in the Custom URL Scheme handler. Specially crafted URLs using custom URL schemes can bypass intended validation and redirect users to attacker-controlled or unintended websites, enabling phishing or malware delivery.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data>= 7.3.6, < 9.30.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify Yappli platform version in your Android appInspect your Android project's build.gradle (or equivalent) file to find the Yappli SDK/platform dependency version. Look for a dependency like 'com.yappli:platform' or similar Yappli library with a version number.Affected if The listed version is 7.3.6 or higher but lower than 9.30.0
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Check if Custom URL Scheme handler is configuredExamine your AndroidManifest.xml file for intent-filter definitions with custom URL schemes (such as yappli://, yourapp://, or other proprietary schemes). Look for <intent-filter> elements containing <data android:scheme="..."/>Affected if Custom URL scheme intent-filters are defined in the manifest
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Verify the APK uses the vulnerable Yappli versionDecompile the deployed APK using apktool or similar tool, then search the resulting files for Yappli platform library version strings (often found in classes.dex, libraries, or configuration files).Affected if The bundled library version in the APK is 7.3.6 or higher but lower than 9.30.0 and the app handles URL schemes
Your environment is affected if your Android app embeds the Yappli platform library version 7.3.6 through 9.29.x and utilizes Custom URL Scheme handling for deep linking.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped9.30.0
Update Yappli platform to version 9.30.0 or later, then rebuild and redeploy all affected Android applications with the fixed platform version.
Yappli v9.30.0 or later
- Upgrade the Yappli SDK/library used in the Android application to version 9.30.0 or later
- After upgrading, rebuild and redeploy the Android application to ensure the fix is applied
- Verify that the Custom URL Scheme handler now properly validates authorization before redirecting
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-20873 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-20873 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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