How severe is CVE-2021-27917?

CVE-2021-27917 has a CVSS score of 5.4/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-27917?

CVE-2021-27917 affects the following packages: mautic/core-lib (Packagist), mautic/core-lib (Packagist), mautic/core (Packagist), mautic/core (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2021-27917?

Update mautic/core-lib to 4.4.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-27917 is resolved across your whole dependency graph.

How do I detect CVE-2021-27917 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mautic/core-lib, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-27917 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-2021-27917 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-27917 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-2021-27917?

CVE-2021-27917 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 22th 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-2021-27917?

CVE-2021-27917 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-2021-27917 published, and has it been updated?

CVE-2021-27917 was published on September 18, 2024 and was last updated on October 20, 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-2021-27917 — core-lib

MEDIUMFix: mautic/mautic@550e335

CVE-2021-27917 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in mautic/core-lib. A fix is available for mautic/core-lib — see the affected versions and patch details below.

Mautic has an XSS in contact tracking and page hits report

Also known asGHSA-xpc5-rr39-v8v2

Published

Sep 18, 2024

Updated

Oct 20, 2026

Affected

4 pkgs

Patched

4 / 4

Exploits

None indexed

Exploitation data as of Nov 2, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2021-27917.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs22th percentile — riskier than 22% of all scored CVEsHighest risk

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

4 pkgs affected

🐘mautic/core-lib🐘mautic/core-lib🐘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

Summary

Prior to this patch, a stored XSS vulnerability existed in the contact tracking and page hits report.

Patches

Please update to 4.4.13 or 5.1.1 or later.

Workarounds

None

References

https://owasp.org/www-project-top-ten/2017/A7_2017-Cross-Site_Scripting_(XSS) https://owasp.org/www-project-web-security-testing-guide/latest/4-Web_Application_Security_Testing/07-Input_Validation_Testing/02-Testing_for_Stored_Cross_Site_Scripting

If you have any questions or comments about this advisory:

Email us at [email protected]

Affected Packages

4 total 4 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`mautic/core-lib`	≥ 1.0.0-beta4&&< 4.4.13	4.4.13`composer require mautic/core-lib:^4.4.13`
🐘Packagist	`mautic/core-lib`	≥ 5.0.0-alpha&&< 5.1.1	5.1.1`composer require mautic/core-lib:^5.1.1`
🐘Packagist	`mautic/core`	≥ 1.0.0-beta4&&< 4.4.13	4.4.13`composer require mautic/core:^4.4.13`
🐘Packagist	`mautic/core`	≥ 5.0.0-alpha&&< 5.1.1	5.1.1`composer require mautic/core:^5.1.1`

Affected Products

1 product · 8 configurations

Application

mauticacquia

≥ 5.0.0 && < 5.1.1

1 version

1.0.0

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-lib, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update mautic/core-lib to 4.4.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-27917 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

### Summary Prior to this patch, a stored XSS vulnerability existed in the contact tracking and page hits report. ### Patches Please update to 4.4.13 or 5.1.1 or later. ### Workarounds None ### References https://owasp.org/www-project-top-ten/2017/A7_2017-Cross-Site_Scripting_(XSS) https://owasp.org/www-project-web-security-testing-guide/latest/4-Web_Application_Security_Testing/07-Input_Validation_Testing/02-Testing_for_Stored_Cross_Site_Scripting If you have any questions or comments about this advisory: Email us at [[email protected]](mailto:[email protected])