CVE-2025-21547: Oracle Hospitality Opera 5 DOS Vulnerability

CVE-2025-21547 Overview

CVE-2025-21547 is a critical vulnerability affecting the Oracle Hospitality OPERA 5 product, specifically within the Opera Servlet component. This vulnerability allows an unauthenticated attacker with network access via HTTP to compromise Oracle Hospitality OPERA 5 systems. The flaw is classified as easily exploitable, requiring no privileges or user interaction to successfully attack vulnerable systems.

Successful exploitation of this vulnerability can result in unauthorized access to critical data or complete access to all Oracle Hospitality OPERA 5 accessible data. Additionally, attackers can cause a complete denial of service condition through a hang or frequently repeatable crash of the affected system.

Critical Impact

This vulnerability enables unauthenticated remote attackers to access sensitive hospitality data and cause complete system denial of service, potentially disrupting hotel and hospitality operations.

Affected Products

• Oracle Hospitality OPERA 5 version 5.6.19.20
• Oracle Hospitality OPERA 5 version 5.6.25.8
• Oracle Hospitality OPERA 5 version 5.6.26.6
• Oracle Hospitality OPERA 5 version 5.6.27.1

Discovery Timeline

• 2025-01-21 - CVE-2025-21547 published to NVD
• 2025-06-23 - Last updated in NVD database

Technical Details for CVE-2025-21547

Vulnerability Analysis

This vulnerability resides in the Opera Servlet component of Oracle Hospitality OPERA 5, a widely deployed property management system used throughout the hospitality industry. The flaw allows unauthenticated attackers to remotely access the system over HTTP without requiring any credentials or user interaction.

The vulnerability impacts both confidentiality and availability of affected systems. From a confidentiality perspective, attackers can gain unauthorized access to critical hospitality data, which may include guest information, reservation details, financial records, and other sensitive business data managed by the OPERA 5 platform. From an availability standpoint, the vulnerability enables attackers to cause complete denial of service through system crashes or hangs, which can severely impact hotel operations.

The ease of exploitation combined with the network-based attack vector makes this vulnerability particularly dangerous for internet-exposed OPERA 5 deployments.

Root Cause

The vulnerability is attributed to CWE-400: Uncontrolled Resource Consumption. This weakness occurs when the Opera Servlet component fails to properly limit the allocation of system resources in response to incoming HTTP requests. Without proper resource management controls, an attacker can craft requests that consume excessive memory, CPU, or other system resources, leading to denial of service conditions or information disclosure through resource exhaustion behaviors.

Attack Vector

The attack vector for CVE-2025-21547 is network-based, requiring only HTTP access to the vulnerable Oracle Hospitality OPERA 5 servlet. An unauthenticated attacker can exploit this vulnerability by sending specially crafted HTTP requests to the Opera Servlet component.

The attack requires no authentication credentials, no privileges on the target system, and no user interaction to execute successfully. This makes the vulnerability particularly attractive for opportunistic attacks against internet-facing OPERA 5 deployments.

The vulnerability mechanism involves sending malicious HTTP requests that trigger uncontrolled resource consumption within the Opera Servlet. This can lead to memory exhaustion, CPU saturation, or other resource depletion scenarios that either expose sensitive data through error conditions or cause the application to crash or hang. For specific technical details regarding the exploitation mechanism, refer to the Oracle Critical Patch Update Advisory.

Detection Methods for CVE-2025-21547

Indicators of Compromise

• Unusual HTTP request patterns targeting the Opera Servlet endpoints
• Unexpected spikes in resource consumption (memory, CPU) on OPERA 5 servers
• Application crashes or hangs in the Oracle Hospitality OPERA 5 service
• Error logs indicating resource exhaustion or out-of-memory conditions
• Unauthorized data access attempts reflected in application audit logs

Detection Strategies

• Monitor HTTP traffic to OPERA 5 servers for anomalous request volumes or malformed requests
• Implement network intrusion detection rules to identify exploitation attempts targeting the Opera Servlet
• Deploy application performance monitoring to detect resource exhaustion conditions
• Enable verbose logging on Oracle Hospitality OPERA 5 to capture suspicious activity
• Use web application firewalls (WAF) to filter potentially malicious HTTP requests

Monitoring Recommendations

• Configure alerts for abnormal resource utilization thresholds on OPERA 5 application servers
• Implement continuous monitoring of Oracle Hospitality OPERA 5 service availability
• Review HTTP access logs regularly for suspicious patterns from unauthenticated sources
• Monitor for repeated application restarts or crash recovery events

How to Mitigate CVE-2025-21547

Immediate Actions Required

• Apply the Oracle Critical Patch Update from January 2025 immediately to all affected systems
• Review network segmentation to limit exposure of OPERA 5 servers to untrusted networks
• Implement rate limiting on HTTP requests to the Opera Servlet component
• Enable enhanced logging and monitoring on all OPERA 5 deployments
• Conduct an inventory of all Oracle Hospitality OPERA 5 installations to identify vulnerable versions

Patch Information

Oracle has addressed this vulnerability in their January 2025 Critical Patch Update. Organizations running affected versions (5.6.19.20, 5.6.25.8, 5.6.26.6, or 5.6.27.1) should apply the security patch as soon as possible. Detailed patch information and download links are available in the Oracle Critical Patch Update Advisory for January 2025.

Workarounds

• Restrict network access to OPERA 5 servers using firewall rules to limit exposure to trusted IP ranges only
• Deploy a web application firewall (WAF) in front of OPERA 5 to filter malicious HTTP requests
• Implement request rate limiting at the network or application layer to mitigate resource exhaustion attacks
• Consider temporarily disabling internet-facing access to OPERA 5 systems until patches can be applied

# Example: Configure firewall rules to restrict access to OPERA 5 server
# Allow only trusted management networks
iptables -A INPUT -p tcp --dport 80 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP