How severe is CVE-2021-27902?

CVE-2021-27902 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-2021-27902?

CVE-2021-27902 affects the following packages: craftcms/cms (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2021-27902?

Update craftcms/cms to 3.6.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-27902 is resolved across your whole dependency graph.

How do I detect CVE-2021-27902 in my Packagist dependencies?

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

How do I mitigate CVE-2021-27902 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-2021-27902 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-27902 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-2021-27902?

CVE-2021-27902 has an EPSS (Exploit Prediction Scoring System) score of 1.0%, placing it in the 61th 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-2021-27902?

CVE-2021-27902 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-2021-27902 published, and has it been updated?

CVE-2021-27902 was published on June 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-2021-27902 — cms

MEDIUMFix: craftcms/cms@8ee85a8

CVE-2021-27902 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in craftcms/cms. A fix is available for craftcms/cms — see the affected versions and patch details below.

Craft CMS Cross-site Scripting Vulnerability

Also known asGHSA-3jxh-789f-p7m6

Published

Jun 30, 2021

Updated

Aug 7, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.0%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs61th percentile — riskier than 61% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-27902 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

1 pkg affected

🐘craftcms/cms

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

An issue was discovered in Craft CMS before 3.6.0. In some circumstances, a potential XSS vulnerability existed in connection with front-end forms that accepted user uploads.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`craftcms/cms`	all versions	3.6.0`composer require craftcms/cms:^3.6.0`

Affected Products

1 product · 1 configurations

Application

craft cmscraftcms

< 3.6.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for craftcms/cms, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update craftcms/cms to 3.6.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-27902 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

An issue was discovered in Craft CMS before 3.6.0. In some circumstances, a potential XSS vulnerability existed in connection with front-end forms that accepted user uploads.

O3 Security · Impact-Aware SCA

Is CVE-2021-27902 in your dependencies?

Find it across Packagist, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

6.1/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CWE Classification

CWE-79Cross-site Scripting (XSS)

Weaponization

No known public exploit tooling found.

OpenSSF Scorecard

Package health score

cms

5.2/10

Maintained10/10

Code-Review0/10

Branch-Protection3/10

Assessed Oct 5, 2026

Timeline

Disclosed

Jun 30, 2021

Last updated

Aug 7, 2026

Identifiers

CVE-2021-27902

GHSA-3jxh-789f-p7m6

References

Advisorygithub.com Advisorygithub.com Advisorynvd.nist.gov Fixgithub.com

Related vulnerabilities

This CVE is medium severity; 7 of 8 other CVEs affecting craftcms/cms are rated as high or higher (top: critical).

GHSA-wg23-69c2-gjc8CVE-2026-72778GHSA-2rp4-x2j7-qmccCVE-2026-72782CVE-2026-72783CVE-2026-72779CVE-2026-14793CVE-2026-72781

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedAug 7, 2026