CVE-2025-36423: IBM Db2 Denial of Service Vulnerability

CVE-2025-36423 Overview

IBM Db2 for Linux, UNIX and Windows (includes Db2 Connect Server) versions 12.1.0 through 12.1.3 contains a vulnerability that could allow a local user to cause a denial of service. The vulnerability stems from improper neutralization of special elements in data query logic, which can be exploited by an authenticated local attacker to disrupt database availability.

Critical Impact

This vulnerability enables local authenticated attackers to trigger denial of service conditions in IBM Db2 database instances, potentially causing significant operational disruptions for organizations relying on Db2 for critical business operations.

Affected Products

• IBM Db2 for Linux 12.1.0 - 12.1.3
• IBM Db2 for UNIX 12.1.0 - 12.1.3
• IBM Db2 for Windows 12.1.0 - 12.1.3 (includes Db2 Connect Server)

Discovery Timeline

• January 30, 2026 - CVE-2025-36423 published to NVD
• February 5, 2026 - Last updated in NVD database

Technical Details for CVE-2025-36423

Vulnerability Analysis

This vulnerability is classified under CWE-1284 (Improper Validation of Specified Quantity in Input), indicating that the IBM Db2 database engine fails to properly validate or neutralize certain special elements within data query logic. When a local user with database access crafts specific queries containing these special elements, the database engine mishandles the input, leading to resource exhaustion or system instability.

The vulnerability requires local access to the system and low-privilege authentication, making it an insider threat or post-compromise exploitation scenario. The impact is limited to availability—there is no compromise of data confidentiality or integrity.

Root Cause

The root cause of CVE-2025-36423 lies in improper input validation within the Db2 query processing engine. When handling certain data query constructs, the database fails to properly neutralize special elements, allowing malformed or crafted queries to consume excessive system resources or trigger error conditions that result in service disruption.

Attack Vector

The attack requires a local user with authenticated access to the Db2 database. The attacker must be able to submit queries to the database engine, either through a direct database connection or via an application that interfaces with Db2. By crafting queries with specific special elements that exploit the improper neutralization flaw, the attacker can cause the database service to become unresponsive or crash.

The vulnerability exploitation pattern involves:

1. Establishing an authenticated connection to the local Db2 instance
2. Submitting specially crafted queries containing malicious special elements
3. The database engine improperly processes these elements
4. Resource exhaustion or error conditions cause denial of service

Detection Methods for CVE-2025-36423

Indicators of Compromise

• Unusual database query patterns containing malformed or unexpected special characters in query logic
• Unexpected Db2 service crashes or restarts without apparent cause
• Database performance degradation or unresponsive queries from local user sessions
• Elevated resource consumption (CPU/memory) by Db2 processes during query execution

Detection Strategies

• Monitor Db2 diagnostic logs (db2diag.log) for unusual error messages related to query parsing or execution failures
• Implement database activity monitoring to detect anomalous query patterns from local user accounts
• Configure alerts for unexpected Db2 service terminations or automatic restarts
• Audit local user accounts with database access privileges for suspicious activity patterns

Monitoring Recommendations

• Enable comprehensive audit logging for all database queries, particularly from local connections
• Configure system monitoring for Db2 process health and resource utilization thresholds
• Implement real-time alerting for database availability issues and service interruptions
• Review database access logs regularly to identify accounts submitting unusual query constructs

How to Mitigate CVE-2025-36423

Immediate Actions Required

• Apply the security patch from IBM as soon as it becomes available for your Db2 version
• Review and restrict local user access to Db2 database instances following the principle of least privilege
• Implement network segmentation to limit local access to database servers
• Enable enhanced monitoring and logging for all Db2 database activity

Patch Information

IBM has published a security advisory addressing this vulnerability. Organizations running affected versions of IBM Db2 (12.1.0 - 12.1.3) should consult the IBM Support Page for detailed patch information, download links, and installation instructions. Prioritize patching based on the criticality of your Db2 deployments and exposure to local user access.

Workarounds

• Restrict database access to only essential personnel and applications until the patch can be applied
• Implement query monitoring and filtering at the application layer to detect potentially malicious query patterns
• Consider running Db2 in a more isolated environment with reduced local user access
• Enable Db2 resource limits and query timeout configurations to minimize impact of potential exploitation attempts

# Example: Review Db2 version to determine vulnerability status
db2level

# Example: Check current database manager configuration for auditing
db2 get dbm cfg | grep -i audit

# Example: Enable audit logging if not already configured
db2audit configure scope all status both
db2audit start