CVE-2020-21246 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in sheng/yiicms. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for sheng/yiicms — see the affected versions and patch details below.
YiiCMS Cross Site Scripting vulnerability
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2020-21246.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
sheng/yiicmsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
Cross Site Scripting vulnerability in YiiCMS v.1.2.0 and prior allows a remote attacker to execute arbitrary code via the news function.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | sheng/yiicms | all versions | 1.2.1composer require sheng/yiicms:^1.2.1 |
Affected Products
yiicmsyiicms_projectResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for sheng/yiicms, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update sheng/yiicms to 1.2.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-21246 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2020-21246 in your dependencies?
Find it across Packagist, including transitive dependencies.