CVE-2021-25929 is a medium-severity (CVSS 4.8) Cross-site Scripting (XSS) vulnerability in org.opennms:opennms. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for org.opennms:opennms — see the affected versions and patch details below.
Cross-site Scripting in OpenNMS Horizon
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2021-25929.
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
org.opennms:opennmsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
In OpenNMS Horizon, versions opennms-1-0-stable through opennms-27.1.0-1; OpenNMS Meridian, versions meridian-foundation-2015.1.0-1 through meridian-foundation-2019.1.18-1; meridian-foundation-2020.1.0-1 through meridian-foundation-2020.1.6-1 are vulnerable to Stored Cross-Site Scripting since there is no validation on the input being sent to the name parameter in noticeWizard endpoint. Due to this flaw an authenticated attacker could inject arbitrary script and trick other admin users into downloading malicious files.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.opennms:opennms | ≥ 1.0.0&&< 27.1.1 | 27.1.1org.opennms:opennms:27.1.1 |
Affected Products
horizonopennmsmeridianopennmsResearch 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 org.opennms:opennms, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.opennms:opennms to 27.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-25929 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-2021-25929 in your dependencies?
Find it across Maven, including transitive dependencies.