CVE-2026-115935: Control panel only API response emulation replaces "securityKey" and reaches server RCE

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-23 · updated 2026-10-26
Weakness: CWE-94

Description

The app/process-api-response-headers action accepts fake Craft API response headers from any authenticated control panel user. A non-admin user with only accessCp can place newline characters in X-Craft-Plugin-Licenses. Craft passes this value to its .env writer without removing the newlines. This lets the user insert a new attacker-known CRAFT_SECURITY_KEY into .env. After Craft loads that key, the user can forge a signed login redirect containing a Twig system() callback. This is different from the previous report. That report reads the existing key through a Twig sandbox bypass. This report replaces the key through fake API headers and CRLF injection. Fixing either source does not fix the other.

Affected products

craftcms cms: from 5.0.0 before 5.11.2; from 4.0.0 before 4.18.9 — fixed in 4.18.9, 5.11.2

How to fix

Upgrade to a fixed version: craftcms cms 4.18.9, 5.11.2. Check the vendor advisory for mitigations.

References

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