Detect CVE-2026-48062: CodeIgniter4 File Upload Extension Validation Bypass (ext_in Rule) in CrowdStrike LogScale
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
LogScale Detection Query
event_simpleName IN (FileCreate, FileWritten, ProcessRollup2)
| filter FileName=/(?i)\.(php[0-9]?|phtml|phar|shtml|pht)$/ AND FilePath=/(?i)(upload|writable|public|tmp|cache)/
OR (ImageFileName=/(?i)(php|php-fpm|httpd|apache2|nginx)/ AND CommandLine=/(?i)(cmd|exec|shell|system|passthru|eval)/)
| eval risk=case(
FilePath=~/(?i)(upload|writable)/ AND FileName=~/(?i)\.php$/, "CRITICAL",
FilePath=~/(?i)public/ AND FileName=~/(?i)\.(phtml|phar)$/, "HIGH",
true(), "MEDIUM"
)
| stats count() as event_count, values(FilePath) as paths, values(FileName) as filenames, values(ComputerName) as hosts by aid, risk
| filter event_count > 0
| sort -event_countCrowdStrike Falcon CQL detecting file creation events involving PHP-family scripts in web upload directories and suspicious process activity by web server parent processes, surfacing potential CodeIgniter4 ext_in bypass exploitation.
Data Sources
Required Tables
False Positives & Tuning
- Endpoint agents on development workstations where PHP files are created in local upload test directories
- Software deployment agents writing PHP application files during legitimate update cycles
- Web application frameworks invoking PHP subprocesses for legitimate background task execution
- Antivirus or EDR quarantine operations moving PHP files to monitored directories
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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