CVE-2024-40075: Laravel v11.x XXE Vulnerability

CVE-2024-40075 Overview

CVE-2024-40075 is an XML External Entity (XXE) vulnerability discovered in Laravel v11.x, the popular PHP web application framework. XXE vulnerabilities occur when an application parses XML input containing references to external entities, potentially allowing attackers to access sensitive files, perform server-side request forgery, or cause denial of service conditions.

Critical Impact

This XXE vulnerability in Laravel v11.x could allow authenticated attackers to trigger denial of service conditions through malicious XML parsing, impacting application availability.

Affected Products

• Laravel v11.x

Discovery Timeline

• July 22, 2024 - CVE-2024-40075 published to NVD
• December 02, 2024 - Last updated in NVD database

Technical Details for CVE-2024-40075

Vulnerability Analysis

This vulnerability falls under CWE-611 (Improper Restriction of XML External Entity Reference), a well-documented security weakness in XML parsers. When an application processes XML input without properly disabling external entity resolution, attackers can craft malicious XML documents that reference external resources.

In the context of Laravel v11.x, the vulnerability exists in XML parsing functionality where external entity processing has not been properly restricted. An authenticated attacker with network access can exploit this weakness to cause resource exhaustion on the target server.

The attack requires low privileges and no user interaction, making it relatively straightforward for authenticated users to exploit. While the vulnerability does not directly compromise confidentiality or integrity, it can significantly impact the availability of affected Laravel applications.

Root Cause

The root cause of CVE-2024-40075 is the improper configuration of XML parsing components within Laravel v11.x. When XML parsers are instantiated without explicitly disabling external entity processing, they may resolve references to external resources defined in DTD (Document Type Definition) declarations within XML documents.

This configuration oversight allows attackers to include specially crafted DTD declarations that reference external entities, which the parser attempts to resolve. The parser's attempt to fetch these external resources can lead to resource exhaustion and denial of service.

Attack Vector

The attack is executed over the network by an authenticated user. The attacker crafts a malicious XML payload containing external entity references and submits it to an endpoint that processes XML input. The vulnerable XML parser processes the document and attempts to resolve the external entities, potentially causing the application to hang or consume excessive resources.

A typical XXE attack payload includes a DOCTYPE declaration with an external entity definition that references a resource designed to cause resource exhaustion, such as a recursive entity expansion (billion laughs attack) or references to slow-responding external endpoints.

For detailed technical information about this vulnerability, refer to the Gitee Laravel Bug Report.

Detection Methods for CVE-2024-40075

Indicators of Compromise

• Presence of malformed or suspicious XML payloads in application logs containing <!DOCTYPE> declarations with <!ENTITY> definitions
• Unusual spikes in server resource consumption (CPU, memory) correlated with XML processing operations
• Network connections initiated from the web server to unexpected external endpoints
• Application timeouts or errors specifically related to XML parsing functions

Detection Strategies

• Monitor application logs for XML parsing errors or exceptions that may indicate exploitation attempts
• Implement Web Application Firewall (WAF) rules to detect and block XML payloads containing external entity declarations
• Configure intrusion detection systems to alert on patterns associated with XXE attacks, such as SYSTEM or PUBLIC identifiers in XML input
• Review audit logs for authenticated users submitting XML content to identify potential attackers

Monitoring Recommendations

• Enable verbose logging for XML parsing operations in Laravel applications to capture detailed error information
• Set up alerts for abnormal resource consumption patterns that could indicate a denial of service attack in progress
• Monitor outbound network connections from application servers for unexpected external requests
• Regularly audit and review application endpoints that accept XML input

How to Mitigate CVE-2024-40075

Immediate Actions Required

• Audit all Laravel v11.x applications to identify endpoints that process XML input
• Disable external entity processing in all XML parsers used by the application by setting libxml_disable_entity_loader(true) (PHP < 8.0) or using appropriate parser flags
• Implement input validation to reject XML documents containing DOCTYPE declarations
• Consider upgrading to a patched version of Laravel when available

Patch Information

No official vendor patch information is currently available in the CVE data. Organizations should monitor the official Laravel security channels and GitHub repository for security updates addressing this vulnerability. In the meantime, implementing the workarounds below can help mitigate the risk.

For additional details about this vulnerability, refer to the Gitee Laravel Bug Report.

Workarounds

• Configure PHP's XML parsing functions to disable external entity loading before processing any XML input
• Implement strict input validation that rejects XML documents containing DOCTYPE declarations or external entity references
• Use Web Application Firewall rules to filter out XML payloads with suspicious DTD declarations
• Consider replacing XML parsing with JSON-based data exchange where feasible to eliminate the XXE attack surface

# PHP configuration to disable external entities in XML parsing
# Add to your XML processing code before parsing any XML input

# For PHP < 8.0
libxml_disable_entity_loader(true);

# For DOMDocument
$dom = new DOMDocument();
$dom->loadXML($xml, LIBXML_NOENT | LIBXML_DTDLOAD | LIBXML_DTDATTR);

# For SimpleXML with entity loading disabled
$previousValue = libxml_disable_entity_loader(true);
$xml = simplexml_load_string($xmlString, 'SimpleXMLElement', LIBXML_NOENT);
libxml_disable_entity_loader($previousValue);