CVE-2026-6052: IBM Db2 Denial of Service Vulnerability

CVE-2026-6052 Overview

CVE-2026-6052 is a denial-of-service vulnerability in IBM Db2 affecting versions 11.5.0 through 11.5.9 and 12.1.0 through 12.1.4. The flaw allows an authenticated attacker to exhaust server memory by executing specific queries against Multi-Dimensional Clustering (MDC) tables. The defect maps to CWE-400: Uncontrolled Resource Consumption and impacts database availability without exposing data confidentiality or integrity.

Critical Impact

An authenticated attacker can trigger out-of-memory conditions on the Db2 server, leading to service disruption for all database users and dependent applications.

Affected Products

• IBM Db2 versions 11.5.0 through 11.5.9
• IBM Db2 versions 12.1.0 through 12.1.4
• Db2 deployments using Multi-Dimensional Clustering (MDC) tables

Discovery Timeline

• 2026-05-27 - CVE-2026-6052 published to NVD
• 2026-05-27 - Last updated in NVD database

Technical Details for CVE-2026-6052

Vulnerability Analysis

The vulnerability resides in how IBM Db2 processes certain queries against Multi-Dimensional Clustering (MDC) tables. MDC tables organize data along multiple dimensions to accelerate analytic workloads. When specific query patterns reach the optimizer or execution engine, Db2 allocates memory without enforcing adequate upper bounds.

Repeated or crafted execution of these queries drives the database instance toward memory exhaustion. The condition affects availability and can impact unrelated sessions sharing the same instance. The attacker requires low privileges and no user interaction, and the attack is delivered over the network through standard Db2 client protocols.

IBM has not published exploit details beyond the advisory. See the IBM Support Page for vendor-confirmed technical context.

Root Cause

The root cause is uncontrolled resource consumption [CWE-400] during query processing against MDC tables. Db2 fails to constrain memory allocation for certain MDC-related query execution paths. As resident memory grows, the database process either crashes or triggers operating system kill conditions.

Attack Vector

Exploitation requires an authenticated session with permission to query MDC tables. The attacker submits crafted SQL targeting MDC structures over the standard Db2 network listener. No special tooling is required beyond a Db2 client capable of submitting parameterized queries.

No verified proof-of-concept code is publicly available. Refer to the IBM Support Page for guidance.

Detection Methods for CVE-2026-6052

Indicators of Compromise

• Db2 instance crashes or restarts correlated with db2sysc process memory growth
• Operating system OOM-killer events terminating Db2 processes on the database host
• Repeated long-running or memory-intensive queries against MDC tables from a single authenticated user
• Sudden spikes in MON_GET_MEMORY_POOL or MON_GET_MEMORY_SET metrics tied to query execution

Detection Strategies

• Audit Db2 query logs for unusual query patterns referencing MDC-organized tables
• Correlate db2diag.log entries reporting memory allocation failures with active session identifiers
• Baseline normal memory usage per workload and alert on deviations exceeding established thresholds

Monitoring Recommendations

• Enable Db2 audit policies for SQL statement execution against MDC tables
• Forward db2diag.log and OS-level memory metrics to a centralized SIEM for correlation
• Track per-user query cost and memory consumption using Db2 workload management (WLM) thresholds
• Alert when any session approaches configured INSTANCE_MEMORY or DATABASE_MEMORY ceilings

How to Mitigate CVE-2026-6052

Immediate Actions Required

• Apply the fixed Db2 release referenced in the IBM Support Page
• Restrict query privileges on MDC tables to trusted application accounts only
• Enforce Db2 workload management limits on memory and execution time per query
• Review recent authenticated sessions for anomalous MDC query activity

Patch Information

IBM has published remediation guidance and fixed versions on the IBM Support Page for CVE-2026-6052. Upgrade Db2 11.5 and 12.1 deployments to the patched fix pack identified by IBM. Validate the fix in a non-production environment before promoting to production database servers.

Workarounds

• Use Db2 Workload Manager (WLM) to cap per-statement memory using SQLRULES thresholds
• Revoke direct query access on MDC tables from interactive user roles where feasible
• Configure INSTANCE_MEMORY hard limits to prevent host-level memory exhaustion
• Throttle concurrent query execution for sessions that target MDC-organized tables

# Example: Apply a WLM activity threshold to limit estimated query cost
db2 "CREATE THRESHOLD LIMIT_MDC_MEM \
     FOR DATABASE ACTIVITIES \
     ENFORCEMENT DATABASE \
     WHEN ESTIMATEDSQLCOST > 100000 \
     STOP EXECUTION"

# Example: Set instance memory ceiling
db2 UPDATE DBM CFG USING INSTANCE_MEMORY 8000000