How severe is CVE-2021-27909?

CVE-2021-27909 has a CVSS score of 6.1/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-27909?

CVE-2021-27909 affects the following packages: mautic/core (Packagist), mautic/core (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2021-27909?

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.

How do I detect CVE-2021-27909 in my Packagist dependencies?

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.

How do I mitigate CVE-2021-27909 if there is no patch (or I can't update yet)?

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 does O3 Security protect against CVE-2021-27909?

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.

Is CVE-2021-27909 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-27909 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-27909?

CVE-2021-27909 has an EPSS (Exploit Prediction Scoring System) score of 3.9%, placing it in the 89th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

Is there exploit tooling available for CVE-2021-27909?

A Nuclei detection template exists for CVE-2021-27909, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2021-27909 published, and has it been updated?

CVE-2021-27909 was published on August 30, 2021 and was last updated on April 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CVE-2021-27909: XSS vulnerability on password reset page (Mediu…

EPSS Exploitation Probability

via FIRST.org ↗

3.9%probability of exploitation in next 30 days

Lower Risk89th percentile-14.79%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

2 pkgs affected

🐘mautic/core🐘mautic/core

Real-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

2 total 2 fixed

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 dependency

Detect
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

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.

O3 Security · Impact-Aware SCA

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.

Scan my dependencies How O3 SCA works

CVE-2021-27909