CVE-2025-36009: IBM Db2 Denial of Service Vulnerability

CVE-2025-36009 is a denial of service vulnerability in IBM Db2 for Linux, UNIX and Windows caused by excessive global variable use. Authenticated users can exploit this flaw to disrupt service availability. This article covers technical details, affected versions, impact assessment, and mitigation strategies.

CVE-2025-36009 Overview

CVE-2025-36009 is a denial of service vulnerability affecting IBM Db2 for Linux, UNIX, and Windows, including DB2 Connect Server. An authenticated user can trigger excessive consumption of a global variable, causing the database service to become unavailable. The vulnerability is categorized under [CWE-1284] (Improper Validation of Specified Quantity in Input).

The flaw requires authenticated network access but has low attack complexity. Successful exploitation impacts availability without affecting confidentiality or integrity. IBM has published a security advisory detailing affected versions and remediation steps.

Critical Impact
Authenticated attackers can render the Db2 database engine unavailable to legitimate users, disrupting dependent applications and services.

Affected Products

IBM Db2 for Linux
IBM Db2 for UNIX
IBM Db2 for Windows (includes DB2 Connect Server)

Discovery Timeline

2026-01-30 - CVE-2025-36009 published to the National Vulnerability Database
2026-02-11 - Last updated in NVD database

Technical Details for CVE-2025-36009

Vulnerability Analysis

The vulnerability resides in how IBM Db2 manages a specific global variable during normal database operations. An authenticated user can repeatedly invoke functionality that exercises this global variable beyond expected bounds. The excessive use exhausts internal resources tied to the variable's lifecycle, leading to a denial of service condition.

Because the attack vector is network-based and requires only low-level privileges, any user with valid Db2 credentials can trigger the condition. The exploit does not require user interaction or elevated privileges. The result is full loss of availability for the affected database instance until administrative intervention restores service.

IBM tracks this issue under [CWE-1284], reflecting improper validation of quantity constraints on input that controls the global variable's usage.

Root Cause

The root cause lies in missing or insufficient validation of how often, or how heavily, the global variable can be referenced within a session. The Db2 engine does not enforce upper bounds on this resource, allowing a single authenticated user to monopolize it. This design flaw transforms a routine operation into an availability risk.

Attack Vector

An attacker authenticates to the Db2 instance using valid credentials over the network. The attacker then issues queries or statements that interact with the vulnerable global variable in a pattern designed to inflate its usage. Sustained interaction exhausts the resource and forces the database into a degraded or unresponsive state. No specialized tooling or custom payloads are required beyond standard Db2 client connectivity.

Verified exploitation code is not publicly available. Refer to the IBM Security Advisory for vendor-supplied technical context.

Detection Methods for CVE-2025-36009

Indicators of Compromise

Repeated database connection sessions from a single authenticated principal exhibiting abnormal query volume against global variable functionality
Db2 instance becoming unresponsive or returning resource-exhaustion errors to legitimate clients
Spikes in Db2 memory or internal resource utilization metrics without a corresponding workload change

Detection Strategies

Monitor Db2 diagnostic logs (db2diag.log) for resource exhaustion warnings and unusual global variable activity
Correlate authentication events with sudden availability degradation on Db2 listener ports
Baseline per-user query patterns and alert on statistical deviations indicative of abuse

Monitoring Recommendations

Enable Db2 audit facility to capture statement-level activity for accounts accessing global variables
Forward Db2 telemetry to a centralized SIEM for correlation with authentication and network logs
Track database health metrics including connection counts, memory pools, and statement execution rates

How to Mitigate CVE-2025-36009

Immediate Actions Required

Apply the fix referenced in the IBM Security Advisory for affected Db2 versions
Restrict Db2 network exposure to trusted application subnets and administrative jump hosts
Review and tighten Db2 user accounts, removing dormant or over-privileged credentials

Patch Information

IBM has published remediation guidance and fix pack information in the official advisory at IBM Support Node 7257695. Administrators should consult the advisory to identify the appropriate fix pack for their Db2 version and platform, then schedule deployment through standard change management.

Workarounds

Enforce least-privilege access controls so only required service accounts can authenticate to Db2
Implement connection rate limiting and query timeouts at the application or network layer to constrain abusive workloads
Monitor authenticated sessions for anomalous patterns and terminate sessions exhibiting resource abuse

bash

# Example: review Db2 authorizations and revoke unnecessary access
db2 "SELECT GRANTEE, DBADMAUTH, CONNECTAUTH FROM SYSIBMADM.DBAUTH"
db2 "REVOKE CONNECT ON DATABASE FROM USER <unused_account>"