Detect CVE-2026-48062: CodeIgniter4 File Upload Extension Validation Bypass (ext_in Rule) in Sumo Logic CSE
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
Sumo Detection Query
_sourceCategory=web/access OR _sourceCategory=linux/syslog
| parse regex "(?<src_ip>\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}) .* \"(?<method>POST|PUT) (?<uri>[^\"]+)\" (?<status>\d{3})"
| where method in ("POST", "PUT")
| where uri matches "*upload*" or uri matches "*writable*" or uri matches "*public*"
| where uri matches "*.php" or uri matches "*.phtml" or uri matches "*.phar" or uri matches "*.php5" or uri matches "*.php7" or uri matches "*.shtml"
| where status in ("200", "201", "204")
| timeslice 1h
| count by _timeslice, src_ip, uri, status
| order by _count descSumo Logic query correlating successful (2xx) HTTP POST/PUT requests uploading PHP-family script files to web upload directories, filtering for confirmed successful uploads that may indicate CodeIgniter4 ext_in exploitation.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate CMS platforms that allow PHP plugin uploads through authenticated admin interfaces
- Automated deployment tools with service accounts uploading application files
- Development environments where PHP files are routinely uploaded for testing
- CDN or proxy log forwarding creating duplicate entries with POST methods
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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