CVE-2026-31941: Chamilo LMS SSRF Vulnerability

CVE-2026-31941 Overview

Chamilo LMS, a widely-used open-source learning management system, contains a Server-Side Request Forgery (SSRF) vulnerability in its Social Wall feature. The vulnerability exists in versions prior to 1.11.38 and 2.0.0-RC.3, where the read_url_with_open_graph endpoint accepts user-supplied URLs via the social_wall_new_msg_main POST parameter and performs server-side HTTP requests without properly validating whether the target is an internal or external resource.

Critical Impact

An authenticated attacker can force the Chamilo server to make arbitrary HTTP requests to internal services, scan internal network ports, and potentially access sensitive cloud instance metadata endpoints, leading to significant information disclosure.

Affected Products

• Chamilo LMS versions prior to 1.11.38
• Chamilo LMS versions prior to 2.0.0-RC.3

Discovery Timeline

• 2026-04-10 - CVE CVE-2026-31941 published to NVD
• 2026-04-13 - Last updated in NVD database

Technical Details for CVE-2026-31941

Vulnerability Analysis

This SSRF vulnerability (CWE-918) in Chamilo LMS arises from insufficient input validation in the Social Wall feature's URL preview functionality. When users share links on the Social Wall, the application attempts to fetch Open Graph metadata from the provided URL to generate rich link previews. The read_url_with_open_graph endpoint processes user-supplied URLs without implementing adequate safeguards to prevent requests to internal network resources.

The vulnerable endpoint performs two separate HTTP requests to the attacker-controlled URL, amplifying the potential for abuse. This design flaw allows authenticated users to leverage the server as a proxy to interact with internal infrastructure that would otherwise be inaccessible from external networks.

Root Cause

The root cause is the lack of URL validation and allowlist/blocklist controls in the read_url_with_open_graph endpoint. The application accepts arbitrary URLs from authenticated users and directly initiates HTTP requests to those destinations without checking whether the target resolves to internal IP addresses (such as 127.0.0.1, 10.x.x.x, 172.16-31.x.x, or 192.168.x.x) or restricted cloud metadata endpoints (like 169.254.169.254).

Attack Vector

The attack requires network access and low-privilege authentication to the Chamilo LMS platform. An attacker with valid user credentials can exploit this vulnerability through the following mechanism:

1. The attacker authenticates to the Chamilo LMS instance
2. Using the Social Wall feature, the attacker submits a POST request to the read_url_with_open_graph endpoint
3. The social_wall_new_msg_main parameter contains a malicious URL pointing to internal resources (e.g., http://169.254.169.254/latest/meta-data/ for AWS metadata or http://127.0.0.1:6379/ for internal Redis)
4. The server makes HTTP requests to the specified internal resource and may leak response data or confirm service availability through timing analysis

This vulnerability enables internal port scanning, access to cloud provider metadata services (potentially exposing IAM credentials), and interaction with internal APIs that lack authentication when accessed from trusted hosts.

Detection Methods for CVE-2026-31941

Indicators of Compromise

• Unusual outbound HTTP requests from the Chamilo web server to internal IP ranges (127.0.0.0/8, 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16)
• HTTP requests to cloud metadata endpoints such as 169.254.169.254 originating from the application server
• Abnormal patterns in Social Wall activity logs showing URLs with internal IP addresses or localhost references
• Web server access logs showing repeated POST requests to the read_url_with_open_graph endpoint with internal network targets

Detection Strategies

• Implement network monitoring to detect outbound connections from web servers to internal network ranges or metadata service IPs
• Configure web application firewalls (WAF) to inspect POST request bodies for internal IP addresses and cloud metadata URLs in the social_wall_new_msg_main parameter
• Enable verbose logging on the Chamilo application to capture all URL fetch requests made by the Social Wall feature
• Deploy intrusion detection rules to alert on SSRF attack patterns targeting the read_url_with_open_graph endpoint

Monitoring Recommendations

• Monitor outbound traffic from the Chamilo server for connections to RFC 1918 private IP ranges and link-local addresses
• Set up alerts for any requests to cloud metadata endpoints (169.254.169.254 for AWS/Azure, metadata.google.internal for GCP)
• Track authentication events correlated with Social Wall URL submission activity to identify potential attacker accounts
• Review web server logs for high volumes of POST requests to Social Wall endpoints from single user sessions

How to Mitigate CVE-2026-31941

Immediate Actions Required

• Upgrade Chamilo LMS to version 1.11.38 or 2.0.0-RC.3 immediately to apply the security fix
• If immediate patching is not possible, consider temporarily disabling the Social Wall feature until the update can be applied
• Implement network-level controls to prevent the web server from initiating connections to internal network ranges
• Review recent Social Wall activity logs for signs of exploitation attempts

Patch Information

Chamilo has released security patches addressing this SSRF vulnerability. The fixes are available in versions 1.11.38 and 2.0.0-RC.3. Security patches can be obtained from the official Chamilo GitHub repository:

• GitHub Commit e3790c5
• GitHub Commit ea6b7b7

For complete vulnerability details, refer to the GitHub Security Advisory GHSA-q74c-mx8x-489h.

Workarounds

• Deploy network segmentation to isolate the Chamilo web server and restrict its ability to reach internal services
• Configure egress firewall rules to block outbound connections from the web server to private IP ranges and metadata endpoints
• Implement a reverse proxy with URL filtering to inspect and block requests containing internal network targets
• If using cloud infrastructure, configure instance metadata service (IMDS) to require session tokens (IMDSv2 on AWS) to mitigate metadata theft via SSRF

# Example iptables rules to block SSRF to internal networks (apply on Chamilo server)
# Block access to localhost from web application
iptables -A OUTPUT -o lo -m owner --uid-owner www-data -j DROP
# Block access to private RFC 1918 ranges
iptables -A OUTPUT -d 10.0.0.0/8 -m owner --uid-owner www-data -j DROP
iptables -A OUTPUT -d 172.16.0.0/12 -m owner --uid-owner www-data -j DROP
iptables -A OUTPUT -d 192.168.0.0/16 -m owner --uid-owner www-data -j DROP
# Block access to cloud metadata endpoint
iptables -A OUTPUT -d 169.254.169.254 -m owner --uid-owner www-data -j DROP