CVE-2026-18424
concretecms concrete cms
Summary
Concrete CMS 9.0.0 to 9.5.2 is vulnerable to Server-Side Request Forgery iremote file import via cross-port reuse of a host's validated DNS pin. When multiple remote URLs share the same host, only the first `ValidatedRemoteUrl` is retained and reused for every later URL with that host. A low-privileged authenticated user permitted to import files could therefore supply a DNS-rebinding host that resolved to a public address during validation and to a private or loopback address during the unpinned download, causing the server to fetch internal-only resources such as loopback services, internal admin panels, or cloud metadata endpoints and to save the responses into the file manager. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 2.1 with vector CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N. Thanks Ahmad Wicaksono (sonix03) for reporting.
Published 2026-09-15 · first seen here 2026-10-10
Analysis & write-ups
No technical write-up from a research team yet. Contact Zero checks Unit 42, Google/Mandiant, Microsoft, Talos, CrowdStrike, Rapid7, watchTowr and others several times a day, plus NVD and CISA reference links.
Where it shows in your logs
Server or web application · Server-side request forgery medium confidence
What to look for
- The server connecting to cloud metadata (169.254.169.254) or internal-only addresses
- Requests whose parameters hold full URLs or internal hostnames
- The application's process (w3wp.exe, java, tomcat, node, php-fpm, httpd, python) starting shells or LOLBins (cmd, powershell, sh, bash, curl, wget, certutil)
- New script files in web roots (.jsp, .aspx, .php): a web shell
- Requests to unusual URLs on the application from internet IPs right before any of the above
- Outbound connections from the server to new external IPs
Data sources
Web server and WAF logs · ATT&CK DS0015 Application Log Content
- Sentinel
W3CIISLogAppServiceHTTPLogsAzureDiagnostics (Application Gateway / Front Door WAF)_Im_WebSession- Splunk
Web.Webms:iis:autoaccess_combinedWAF / proxy sourcetypes- CrowdStrike
Falcon Next-Gen SIEM: third-party web / WAF / proxy logs
Process creation · ATT&CK DS0009 Process Creation
- Sentinel
DeviceProcessEventsSecurityEvent (4688)Sysmon Event ID 1_Im_ProcessCreate- Splunk
Endpoint.ProcessesXmlWinEventLog:Microsoft-Windows-Sysmon/OperationalWinEventLog:Security (4688)- CrowdStrike
ProcessRollup2SyntheticProcessRollup2
File creation · ATT&CK DS0022 File Creation
- Sentinel
DeviceFileEventsSysmon Event ID 11_Im_FileEvent- Splunk
Endpoint.FilesystemSysmon Event ID 11- CrowdStrike
NewExecutableWrittenNewScriptWritten*FileWritten events
Network connections · ATT&CK DS0029 Network Connection Creation / Network Traffic Flow
- Sentinel
DeviceNetworkEventsCommonSecurityLog (firewall)_Im_NetworkSession- Splunk
Network_Traffic.All_TrafficFirewall sourcetypes (pan:traffic, fortigate_traffic, cisco:asa)- CrowdStrike
NetworkConnectIP4NetworkReceiveAcceptIP4NetworkConnectIP6
A generic baseline worked out from the product type and weakness (CWE-918), not a detection. Check table and field names against your environment. Hunt queries for Sigma, Splunk, Sentinel and CrowdStrike are coming.