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Unlock with Pro - from £29/user/moDetect Formie Hidden Field Default Server-Side Template Injection (CVE-2026-52889) in IBM QRadar
Detects exploitation attempts against CVE-2026-52889, a Server-Side Template Injection (SSTI, CWE-1336) vulnerability in the Formie plugin (verbb/formie) for Craft CMS. The vulnerability exists in how Formie processes 'default value' expressions for Hidden form fields, allowing an unauthenticated or low-privileged attacker to inject Twig template syntax that is evaluated server-side, potentially leading to remote code execution. Affects verbb/formie < 3.1.27. Detection focuses on Twig/Craft template injection payload patterns in form submission requests, anomalous POST bodies to Formie submission endpoints, and resulting web shell / RCE indicators (process spawning from PHP-FPM/Craft, outbound connections, file writes to web root).
MITRE ATT&CK
- Tactic
- Initial Access Execution
QRadar Detection Query
SELECT sourceip, destinationip, "URL", payload, eventcount
FROM events
WHERE LOGSOURCETYPENAME(devicetype) ILIKE '%HTTP%'
AND ("URL" ILIKE '%actions/formie%' OR "URL" ILIKE '%formie%')
AND (payload ILIKE '%{{%' OR payload ILIKE '%_self.env%' OR payload ILIKE '%system(%' OR payload ILIKE '%proc_open(%' OR payload ILIKE '%getFilter%')
AND UTF8(payload) ILIKE '%POST%'
GROUP BY sourceip, destinationip, "URL", payload
LAST 24 HOURSDetects POST requests to Formie endpoints in QRadar-normalized HTTP flow/event data containing SSTI payload indicators tied to CVE-2026-52889.
Data Sources
Required Tables
False Positives & Tuning
- Authorized scanning appliances performing periodic web application assessments
- Load balancer health checks that replay cached request bodies containing template-like strings
- False matches from legitimate JSON payloads containing double curly braces unrelated to Twig
Other platforms for CVE-2026-52889
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Formie Hidden Field SSTI Payload Submission
Expected signal: Web server access log entry recording a POST to /actions/formie/submissions/submit containing the Twig SSTI payload string in the request body.
- Test 2Formie SSTI to Command Execution Simulation
Expected signal: EDR/auditd process creation events showing 'bash' spawned as a child of a process running under the www-data (or equivalent web server) user, executing 'id', 'whoami', and 'uname -a'.
- Test 3Formie Malicious Webshell Drop Simulation
Expected signal: File integrity monitoring / EDR file-creation event for a new .php file written under the web root by the web server process user shortly after a Formie form submission.
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