What is CVE-2021-20873?

CVE-2021-20873 is a high-severity vulnerability in Yappli, classified under Missing Authorization. CVSS score: 8.1/10. Published 2021-12-28.

How severe is CVE-2021-20873?

High severity. CVSS v3 base score is 8.1 out of 10.

Auth bypass in Yappli

CVE-2021-20873

Yappli 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.

Vulnerability class: Broken Access Control

Published 2021-12-28 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N.

EPSS exploit prediction

EPSS: 0.008 (56.3th percentile), scored 2026-10-01.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 56th percentile — 56.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: 0.000

Affected products

Yappli
Yappli, Inc. Yappli — versions versions since v7.3.6 and prior to v9.30.0

Weakness classification (CWE)

CWE-862 — Missing Authorization

References

support.yappli.co.jp/hc/ja/articles/4410249902745 (Vendor Advisory)
jvn.jp/en/jp/JVN66422035/index.html (Third Party Advisory)

Frequently asked questions

What is CVE-2021-20873?: CVE-2021-20873 is a high-severity vulnerability in Yappli, classified under Missing Authorization. CVSS score: 8.1/10. Published 2021-12-28.
How severe is CVE-2021-20873?: High severity. CVSS v3 base score is 8.1 out of 10.