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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

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

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.

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 4.1%, placing it in the 90th 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.

What type of vulnerability is CVE-2021-27909?

CVE-2021-27909 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

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 August 7, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘

🐘 Packagist

Not in CISA KEV

MEDIUM severity

CVE-2021-27909 — core

MEDIUMFix: mautic/mautic@942cb69

CVE-2021-27909 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in mautic/core. A fix is available for mautic/core — see the affected versions and patch details below.

XSS vulnerability on password reset page

Also known asGHSA-32hw-3pvh-vcvc

Published

Aug 30, 2021

Updated

Aug 7, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

4.1%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs90th percentile — riskier than 90% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-27909 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

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

Impact

For Mautic versions prior to 3.3.4, 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.

Patches

Upgrade to 3.3.4 or 4.0.0

Workarounds

References

https://github.com/mautic/mautic/releases/tag/3.3.4 https://github.com/mautic/mautic/releases/tag/4.0.0

For more information

If you have any questions or comments about this advisory:

Email us at [email protected]

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`mautic/core`	all versions	3.3.4`composer require mautic/core:^3.3.4`
🐘Packagist	`mautic/core`	≥ 4.0.0-alpha1&&< 4.0.0	4.0.0`composer require mautic/core:^4.0.0`

Affected Products

1 product · 4 configurations

Application

mauticacquia

< 3.3.4

1 version

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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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
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.

How to detect CVE-2021-27909

A community-maintained Nuclei template exists for this CVE. You can scan for it directly:

nuclei -id cve-2021-27909 -u https://target

Template: Mautic <3.3.4 - Cross-Site Scripting
Severity: medium
Impact: Successful exploitation of this vulnerability could allow an attacker to execute arbitrary JavaScript code in the context of the victim's browser, leading to potential data theft or unauthorized actions.
Remediation: Upgrade Mautic to version 3.3.4 or later to mitigate this vulnerability.

Template by ProjectDiscovery nuclei-templates (kiransau), MIT licensed. View the full template. Scan only systems you are authorised to test.

Frequently Asked Questions

### Impact For Mautic versions prior to 3.3.4, 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. ### Patches Upgrade to 3.3.4 or 4.0.0 ### Workarounds No ### References https://github.com/mautic/mautic/releases/tag/3.3.4 https://github.com/mautic/mautic/releases/tag/4.0.0 ### For more information If you have any questions or comments abo