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CRITICAL severity

CVE-2021-27903 — cms

CRITICALFix: craftcms/cms@c17728f

CVE-2021-27903 is a critical-severity (CVSS 9.8) CWE-862 vulnerability in craftcms/cms. A fix is available for craftcms/cms — see the affected versions and patch details below.

Craft CMS Remote Code Injection

Also known asGHSA-x2j7-6hxm-87p3
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 11, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
2.8%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs86th percentile — riskier than 86% of all scored CVEsHighest risk
2.32%2.99%3.66%4.32%3.8%2.8%Apr 26Aug 26Oct 26

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

How urgent is this, really

CVE-2021-27903 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 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 3.6.7. In some circumstances, a potential Remote Code Execution vulnerability existed on sites that did not restrict administrative changes (if an attacker were somehow able to hijack an administrator's session).

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐘Packagistcraftcms/cmsall versions3.6.7composer require craftcms/cms:^3.6.7

Affected Products

1 product · 1 configurations
Application
craft cmscraftcms
< 3.6.7
range

Detection & mitigation playbook

Open-source dependency

  1. 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.

  2. Fix

    Update craftcms/cms to 3.6.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-27903 is resolved across your whole dependency graph.

  3. Workarounds

    Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

An issue was discovered in Craft CMS before 3.6.7. In some circumstances, a potential Remote Code Execution vulnerability existed on sites that did not restrict administrative changes (if an attacker were somehow able to hijack an administrator's session).
O3 Security · Impact-Aware SCA

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CVE-2021-27903: cms RCE — Fixed in 3.6.7