How severe is CVE-2021-27911?

CVE-2021-27911 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-2021-27911?

CVE-2021-27911 affects the following packages: mautic/core (Packagist), mautic/core (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2021-27911?

Update mautic/core to 3.3.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-27911 is resolved across your whole dependency graph.

How do I detect CVE-2021-27911 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-2021-27911 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-2021-27911 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-27911 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-2021-27911?

CVE-2021-27911 has an EPSS (Exploit Prediction Scoring System) score of 0.6%, placing it in the 49th 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-2021-27911?

CVE-2021-27911 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.

When was CVE-2021-27911 published, and has it been updated?

CVE-2021-27911 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-2021-27911 — core

MEDIUM

CVE-2021-27911 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 contacts view

Also known asGHSA-72hm-fx78-xwhc

Published

Aug 30, 2021

Updated

Aug 7, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.6%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs49th percentile — riskier than 49% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-27911 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

Mautic versions before 3.3.4/4.0.0 are vulnerable to an inline JS XSS attack through the contact's first or last name and triggered when viewing a contact's details page then clicking on the action drop down and hovering over the Campaigns button. Contact first and last name can be populated from different sources such as UI, API, 3rd party syncing, forms, etc.

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-2021-27911 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

### Impact Mautic versions before 3.3.4/4.0.0 are vulnerable to an inline JS XSS attack through the contact's first or last name and triggered when viewing a contact's details page then clicking on the action drop down and hovering over the Campaigns button. Contact first and last name can be populated from different sources such as UI, API, 3rd party syncing, forms, etc. ### 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 que