CVE-2026-1718: IBM Db2 Denial of Service Vulnerability

CVE-2026-1718 Overview

CVE-2026-1718 is a denial of service vulnerability affecting IBM Db2 versions 11.5.0 through 11.5.9 and 12.1.0 through 12.1.4. An authenticated attacker can submit a specially crafted query that exhausts database resources when autonomous transactions are enabled. The flaw is classified under [CWE-770] (Allocation of Resources Without Limits or Throttling).

The issue requires network access and low-privileged authentication, with no user interaction. Successful exploitation degrades availability of the affected Db2 instance, disrupting database-dependent applications and services.

Critical Impact

An authenticated attacker can render IBM Db2 instances unavailable by submitting a crafted query against environments where autonomous transactions are enabled.

Affected Products

• IBM Db2 11.5.0 through 11.5.9
• IBM Db2 12.1.0 through 12.1.4
• Db2 deployments with autonomous transactions enabled

Discovery Timeline

• 2026-05-27 - CVE-2026-1718 published to the National Vulnerability Database (NVD)
• 2026-05-27 - Last updated in NVD database

Technical Details for CVE-2026-1718

Vulnerability Analysis

The vulnerability exists in how IBM Db2 processes specific queries when autonomous transactions are enabled. Autonomous transactions allow a routine to execute SQL statements in a separate, independent transaction context from the calling session. Improper resource governance during this processing path lets a crafted query consume excessive resources, leading to denial of service.

The flaw maps to [CWE-770], where the database engine fails to apply adequate limits or throttling on resource allocation. An authenticated session with low privileges is sufficient to trigger the condition over the network. The impact is confined to availability, with limited confidentiality exposure and no integrity impact according to the CVSS vector.

Because the attack requires only standard authenticated access and no user interaction, any user able to submit SQL to an affected instance can disrupt service. Environments that expose Db2 to broad user bases or that run multi-tenant workloads face elevated operational risk.

Root Cause

The root cause is insufficient resource control during autonomous transaction execution. The engine accepts queries that allocate or hold resources without enforcing effective ceilings, allowing a single crafted request to monopolize server capacity. Refer to the IBM Support Page for vendor-confirmed technical details.

Attack Vector

The attack is remote and authenticated. A low-privileged user connects to the Db2 instance over the network and submits the crafted SQL query. No social engineering or local access is required. Exploitation does not yield code execution, data modification, or significant data disclosure, but it can stall database operations until administrator intervention.

No public proof-of-concept code or exploit has been published for this issue. The vulnerability is described in prose because verified exploitation code is not available in the referenced sources.

Detection Methods for CVE-2026-1718

Indicators of Compromise

• Sudden spikes in Db2 CPU, memory, or transaction log utilization tied to a single session or user identity
• Long-running or hung queries originating from low-privileged accounts that invoke autonomous transactions
• Application timeouts, connection pool exhaustion, or health-check failures against the affected Db2 instance

Detection Strategies

• Audit Db2 diagnostic logs (db2diag.log) and event monitors for repeated resource-intensive autonomous transaction calls
• Correlate database session telemetry with network flow data to identify abnormal query patterns from authenticated users
• Baseline normal query duration and resource consumption, then alert on outliers that match the crafted query profile

Monitoring Recommendations

• Enable Db2 workload management and activity event monitoring to capture per-statement resource usage
• Forward Db2 audit and diagnostic logs to a centralized analytics platform for query-level anomaly detection
• Track failed and successful logins for accounts authorized to execute autonomous transactions

How to Mitigate CVE-2026-1718

Immediate Actions Required

• Inventory IBM Db2 instances running 11.5.0 through 11.5.9 and 12.1.0 through 12.1.4 and identify those with autonomous transactions enabled
• Apply the fix referenced in the IBM Support Page as soon as it is available in your environment
• Restrict database connectivity to trusted application hosts using network segmentation and firewall rules
• Review and tighten privileges for accounts that can execute autonomous transactions

Patch Information

IBM has published guidance for CVE-2026-1718 on the IBM Support Page. Administrators should consult the advisory for fixed version numbers, applicable fix packs, and upgrade procedures for both the 11.5.x and 12.1.x branches.

Workarounds

• Disable autonomous transactions where they are not required by application workloads
• Apply Db2 workload management thresholds to cap CPU time, rows returned, and execution time per statement
• Revoke or limit the EXECUTE privilege on routines that invoke autonomous transactions to a minimal set of trusted accounts
• Implement connection-level resource limits and statement timeouts at the application or middleware tier

# Example Db2 workload management threshold to cap statement runtime
db2 "CREATE THRESHOLD limit_long_queries \
  FOR DATABASE ACTIVITIES \
  ENFORCEMENT DATABASE \
  WHEN ACTIVITYTOTALTIME > 5 MINUTES \
  STOP EXECUTION"