Response playbooks, investigation guides, and Atomic Red Team tests are Pro-only. Upgrade to unlock the full detection package for CVE-2026-9558.
Upgrade to ProDetect Mautic Server-Side Template Injection (SSTI) in Theme Templates in IBM QRadar
Detects exploitation of CVE-2026-9558, a critical (CVSS 9.9) Server-Side Template Injection vulnerability in Mautic's theme template engine (CWE-1336, Twig-based SSTI). An authenticated or in some deployments unauthenticated attacker can inject malicious Twig template syntax through theme customization, email/landing page builder, or theme upload/import functionality, achieving remote code execution on the underlying PHP host. Affects mautic/core versions >=1.3.0 <4.4.13, >=5.0.0 <5.2.11, >=6.0.0 <6.0.9, and >=7.0.0 <7.1.2. A public PoC/advisory exists (GHSA-9fx4-7cmj-47vg).
MITRE ATT&CK
- Tactic
- Initial Access Execution
QRadar Detection Query
SELECT sourceip, destinationip, "URL", httpMethod, httpStatusCode, payload, starttime
FROM events
WHERE LOGSOURCETYPENAME(devicetype) ILIKE '%Web%'
AND ("URL" ILIKE '%/s/themes%' OR "URL" ILIKE '%/s/emails%' OR "URL" ILIKE '%/s/pages%' OR "URL" ILIKE '%/theme/upload%' OR "URL" ILIKE '%/api/themes%')
AND httpMethod IN ('POST','PUT')
AND (UTF8(payload) ILIKE '%{{%' OR UTF8(payload) ILIKE '%__construct%' OR UTF8(payload) ILIKE '%system(%' OR UTF8(payload) ILIKE '%getFilter%')
LAST 24 HOURSIdentifies HTTP POST/PUT requests captured by QRadar web/proxy log sources targeting Mautic theme or content endpoints whose payload contains Twig SSTI markers, indicative of CVE-2026-9558 exploitation attempts.
Data Sources
Required Tables
False Positives & Tuning
- Authorized penetration testers actively assessing the Mautic instance under a signed engagement
- Templating documentation or help content being posted through the CMS containing example Twig syntax
- Payload truncation in QRadar causing partial matches on benign JSON/XML content
Other platforms for CVE-2026-9558
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 1Twig SSTI probe against theme endpoint
Expected signal: Web access log entry for POST /s/themes/edit/1 containing the literal string {{7*7}}; if vulnerable, the rendered theme output contains '49'.
- Test 2Twig-to-PHP function call injection
Expected signal: Web log entry showing POST to /s/emails/edit/1 with __construct/getFilter/system( markers; process telemetry showing php-fpm spawning 'id' if the gadget chain succeeds in the lab sandbox.
- Test 3Post-exploitation shell spawn simulation from PHP-FPM
Expected signal: Process creation events showing bash/id/whoami/curl spawned with parent process php-fpm running as www-data, plus an outbound connection to the test callback listener.
Unlock playbooks & atomic tests with Pro
Get the full detection package for CVE-2026-9558 — response playbook and atomic red team tests, plus investigation guidance and hunting queries.
df00tech Pro — £29/user/month