CVE-2023-21918: Oracle Database Recovery Manager DOS Flaw

CVE-2023-21918 Overview

CVE-2023-21918 is a denial of service vulnerability affecting the Oracle Database Recovery Manager (RMAN) component of Oracle Database Server. The vulnerability allows a highly privileged attacker with Local SYSDBA privileges and network access via Oracle Net to cause a complete denial of service condition, resulting in a hang or frequently repeatable crash of the Oracle Database Recovery Manager component.

This vulnerability is particularly concerning because while the flaw exists in Oracle Database Recovery Manager, successful exploitation can significantly impact additional products beyond the vulnerable component (scope change). The attack requires high privileges but is easily exploitable once the attacker has the necessary access.

Critical Impact

Successful exploitation enables attackers with SYSDBA privileges to completely disrupt database recovery operations, potentially impacting business continuity and disaster recovery capabilities across dependent systems.

Affected Products

• Oracle Database Recovery Manager 19c
• Oracle Database Recovery Manager 21c

Discovery Timeline

• April 18, 2023 - CVE-2023-21918 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-21918

Vulnerability Analysis

This vulnerability affects the Oracle Database Recovery Manager (RMAN), a critical component used for backup and recovery operations in Oracle Database environments. The flaw allows an authenticated attacker with elevated privileges to trigger a denial of service condition that can completely crash the RMAN component.

The vulnerability is classified as easily exploitable, meaning that once an attacker has obtained the required Local SYSDBA privileges and network access via Oracle Net, minimal technical skill or effort is needed to trigger the denial of service condition. The scope change designation indicates that the impact extends beyond the vulnerable RMAN component itself, potentially affecting other database services and dependent applications that rely on the database infrastructure.

Root Cause

The specific technical root cause has not been publicly disclosed by Oracle. The vulnerability is categorized under NVD-CWE-noinfo, indicating that detailed weakness enumeration information is not available. However, the nature of the vulnerability—causing hangs or repeatable crashes—suggests potential issues with resource handling, input validation, or state management within the RMAN component when processing certain network requests from privileged users.

Attack Vector

The attack requires the following conditions:

Prerequisites:

• The attacker must have Local SYSDBA privileges on the target Oracle Database
• Network access to the target system via Oracle Net protocol is required
• No user interaction is needed to exploit the vulnerability

Exploitation Method:
The vulnerability can be exploited remotely over the network. An attacker with the necessary privileges sends specially crafted requests through Oracle Net to the Database Recovery Manager component. When these requests are processed, they trigger a condition that causes the RMAN service to hang or crash repeatedly.

The scope change aspect means that while the vulnerability exists in RMAN, the resulting denial of service can cascade to affect other Oracle Database components and services that depend on recovery manager functionality, such as backup operations, point-in-time recovery processes, and data guard configurations.

Detection Methods for CVE-2023-21918

Indicators of Compromise

• Unexpected or repeated crashes of the Oracle Database Recovery Manager (RMAN) process
• Unusual RMAN session activity from privileged accounts, particularly SYSDBA connections
• Database alert logs showing RMAN component failures or abnormal terminations
• Network traffic anomalies on Oracle Net ports (typically 1521) from privileged database sessions

Detection Strategies

• Monitor Oracle Database alert logs for RMAN-related errors, crashes, or hang conditions
• Implement auditing for all SYSDBA connections to track privileged access patterns
• Deploy database activity monitoring solutions to detect anomalous RMAN operations
• Configure real-time alerting for RMAN process state changes and unexpected terminations

Monitoring Recommendations

• Enable Oracle Unified Auditing to capture detailed session and privilege usage information
• Configure Oracle Enterprise Manager or similar tools to monitor RMAN component health
• Establish baseline metrics for RMAN operations to identify deviations that may indicate exploitation attempts
• Review network connection logs for unusual Oracle Net traffic patterns targeting database services

How to Mitigate CVE-2023-21918

Immediate Actions Required

• Apply the Oracle Critical Patch Update (CPU) from April 2023 immediately to all affected Oracle Database installations
• Review and audit all accounts with SYSDBA privileges to ensure least-privilege principles are enforced
• Implement network segmentation to restrict Oracle Net access to authorized systems only
• Enable comprehensive auditing for privileged database operations

Patch Information

Oracle has addressed this vulnerability in the Oracle Critical Patch Update April 2023. Organizations running Oracle Database Server versions 19c or 21c should apply the relevant patches from this CPU as soon as possible.

The April 2023 CPU contains security fixes for multiple Oracle products. Database administrators should review the full advisory to understand all patches applicable to their environment and plan appropriate testing before deployment to production systems.

Workarounds

• Restrict SYSDBA privileges to only essential personnel and service accounts that require this level of access
• Implement network-level controls to limit which hosts can establish Oracle Net connections to database servers
• Consider using Oracle Database Vault to enforce additional access controls on privileged operations
• Deploy intrusion detection systems to monitor for suspicious activity targeting Oracle Database services

# Example: Audit SYSDBA connections in Oracle Database
# Enable unified auditing for SYSDBA operations
ALTER SYSTEM SET audit_trail=db,extended SCOPE=SPFILE;

# Create audit policy for privileged connections
CREATE AUDIT POLICY sysdba_audit_policy
ACTIONS ALL
WHEN 'SYS_CONTEXT(''USERENV'',''SESSION_USER'') = ''SYS'''
EVALUATE PER SESSION;

# Enable the audit policy
AUDIT POLICY sysdba_audit_policy;