CVE-2021-25977 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in Piranha. A fix is available for Piranha — see the affected versions and patch details below.
Cross-site Scripting in PiranhaCMS
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-2021-25977.
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
PiranhaReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
In PiranhaCMS, versions 7.0.0 to 9.1.1 are vulnerable to stored XSS due to the page title improperly sanitized. By creating a page with a specially crafted page title, a low privileged user can trigger arbitrary JavaScript execution.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Piranha | ≥ 7.0.0&&< 9.2.0 | 9.2.0dotnet add package Piranha --version 9.2.0 |
Affected Products
piranha cmsdotnetfoundationDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Piranha, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Piranha to 9.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-25977 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-2021-25977 in your dependencies?
Find it across NuGet, including transitive dependencies.