How severe is CVE-2021-27915?

CVE-2021-27915 has a CVSS score of 9/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-27915?

CVE-2021-27915 affects the following packages: mautic/core (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2021-27915?

Update mautic/core to 4.4.12 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-27915 is resolved across your whole dependency graph.

How do I detect CVE-2021-27915 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-2021-27915 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-2021-27915 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-27915 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-2021-27915?

CVE-2021-27915 has an EPSS (Exploit Prediction Scoring System) score of 0.6%, placing it in the 50th 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-2021-27915?

CVE-2021-27915 is classified as CWE-80 (CWE-80), Cross-site Scripting (XSS) (CWE-79). These weakness types 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-2021-27915 published, and has it been updated?

CVE-2021-27915 was published on September 17, 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

CRITICAL severity

CVE-2021-27915 — core

CRITICALFix: mautic/mautic@2d64839

CVE-2021-27915 is a critical-severity (CVSS 9) CWE-80 vulnerability in mautic/core. A fix is available for mautic/core — see the affected versions and patch details below.

Mautic vulnerable to stored cross-site scripting in description field

Also known asGHSA-2rc5-2755-v422

Published

Sep 17, 2024

Updated

Oct 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

A successful exploit gives an attacker total control of the affected component, not partial access.
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-2021-27915.

EPSS Exploitation Probability

via FIRST.org ↗

0.6%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs50th percentile — riskier than 50% 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

1 pkg affected

🐘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

Prior to the patched version, there is an XSS vulnerability in the description fields within the Mautic application which could be exploited by a logged in user of Mautic with the appropriate permissions.

This could lead to the user having elevated access to the system.

Patches

Update to 4.4.12

Workarounds

None

References

If you have any questions or comments about this advisory:

Email us at [email protected]

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`mautic/core`	≥ 1.0.0-beta2&&< 4.4.12	4.4.12`composer require mautic/core:^4.4.12`

Affected Products

1 product · 9 configurations

Application

mauticacquia

≥ 1.0.0 && < 4.4.12

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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update mautic/core to 4.4.12 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-27915 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 Prior to the patched version, there is an XSS vulnerability in the description fields within the Mautic application which could be exploited by a logged in user of Mautic with the appropriate permissions. This could lead to the user having elevated access to the system. ### Patches Update to 4.4.12 ### 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_Scripti