Detect CVE-2026-48062: CodeIgniter4 File Upload Extension Validation Bypass (ext_in Rule) in Microsoft Sentinel
CVE-2026-48062 affects CodeIgniter4 framework versions prior to 4.7.2. The `ext_in` validation rule fails to properly validate file extensions during upload, allowing attackers to bypass extension restrictions and upload arbitrary files including web shells or malicious executables. This unrestricted file upload vulnerability (CWE-434) has a CVSS score of 9.8 and a public proof-of-concept. Successful exploitation can lead to remote code execution on the hosting server.
MITRE ATT&CK
- Tactic
- Initial Access Execution Persistence
KQL Detection Query
union DeviceFileEvents, DeviceProcessEvents
| where TimeGenerated > ago(7d)
| where DeviceId in (
(DeviceFileEvents
| where FolderPath has_any ("writable", "uploads", "tmp", "cache", "CodeIgniter")
| where FileName has_any (".php", ".phtml", ".php5", ".php7", ".phar", ".shtml", ".pht")
| distinct DeviceId)
)
| where ActionType in ("FileCreated", "FileModified", "ProcessCreated")
| extend FilePath = strcat(FolderPath, "\\", FileName)
| where FilePath has_any ("uploads", "writable", "public", "assets")
| project TimeGenerated, DeviceName, DeviceId, ActionType, FileName, FolderPath, InitiatingProcessFileName, InitiatingProcessCommandLine, AccountName
| order by TimeGenerated descDetects suspicious file creation events where PHP or executable script files are written to web-accessible upload directories, which may indicate exploitation of the CodeIgniter4 ext_in validation bypass.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate PHP application deployments or updates to upload directories
- Automated content management systems writing PHP-based templates to upload paths
- Developer activity placing scripts in writable directories during testing
- Backup or migration tools restoring PHP files to web-accessible paths
Other platforms for CVE-2026-48062
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 1Simulate CodeIgniter4 ext_in Bypass via Crafted Multipart Upload
Expected signal: HTTP POST to upload endpoint with Content-Type image/jpeg but .php file extension; file creation event in upload directory for a .php file; web server process as the initiating process for the file write
- Test 2Web Shell Execution Verification After Upload
Expected signal: HTTP GET requests to PHP file path in upload directory; process tree showing web server (apache2/nginx/php-fpm) spawning shell or system binaries (id, whoami, uname); network connections to external IP if reverse shell payload used
- Test 3Filesystem Reconnaissance via Uploaded Web Shell
Expected signal: Process events for cat, ls, find spawned by php-fpm or apache2 with web server UID; file read events on /etc/passwd and .env files initiated by web server process; auditd SYSCALL records for execve by www-data user
References (6)
- https://github.com/codeigniter4/CodeIgniter4/security/advisories/GHSA-2gr4-ppc7-7mhx
- https://github.com/codeigniter4/CodeIgniter4/commit/29299349e7d232e9532767c7cefaed30957309be
- https://codeigniter.com/user_guide/libraries/uploaded_files.html#moving-files
- https://codeigniter.com/user_guide/libraries/validation.html#rules-for-file-uploads
- https://github.com/codeigniter4/CodeIgniter4/blob/develop/CHANGELOG.md
- https://github.com/advisories/GHSA-2gr4-ppc7-7mhx
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