CVE-2021-27909
MEDIUMCVE-2021-27909 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in mautic/core. O3 Security confirms whether CVE-2021-27909 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
XSS vulnerability on password reset page
Real-World Exposure
mautic/core🐘mautic/coreReal-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
For Mautic versions prior to 3.3.4/4.0.0, there is an XSS vulnerability on Mautic's password reset page where a vulnerable parameter, "bundle," in the URL could allow an attacker to execute Javascript code. The attacker would be required to convince or trick the target into clicking a password reset URL with the vulnerable parameter utilized.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | mautic/core | all versions | 3.3.4 |
| 🐘Packagist | mautic/core | ≥ 4.0.0-alpha1&&< 4.0.0 | 4.0.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mautic/core. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update mautic/core to 3.3.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-27909 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2021-27909 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2021-27909. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-27909 in your dependencies?
O3 detects CVE-2021-27909 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.