CVE-2006-5540 in PostgreSQL
Summary
by MITRE
backend/parser/analyze.c in PostgreSQL 8.1.x before 8.1.5 allows remote authenticated users to cause a denial of service (daemon crash) via certain aggregate functions in an UPDATE statement, which are not properly handled during a "MIN/MAX index optimization."
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Analysis
by VulDB Data Team • 04/25/2026
The vulnerability described in CVE-2006-5540 represents a critical denial of service weakness within the PostgreSQL database management system affecting versions 8.1.x prior to 8.1.5. This flaw specifically resides in the backend/parser/analyze.c file and exploits a design oversight in how the system handles certain aggregate functions during UPDATE operations. The issue manifests when users with authenticated access to the database execute carefully crafted UPDATE statements containing specific aggregate functions that trigger an improper handling path during what should be a routine MIN/MAX index optimization process. The technical implementation flaw stems from insufficient validation and error handling within the query analysis phase, where the system fails to properly account for the interaction between aggregate function evaluation and index optimization algorithms.
The operational impact of this vulnerability extends beyond simple service disruption as it enables authenticated attackers to systematically crash the PostgreSQL daemon through carefully constructed database queries. This type of attack falls under the category of resource exhaustion and daemon termination attacks that can severely impact database availability and business continuity. The vulnerability is particularly dangerous because it requires only authenticated access, meaning that any user with legitimate database credentials can exploit this weakness to cause system-wide outages. The attack vector leverages the database's internal optimization mechanisms, making it difficult to detect through conventional network monitoring approaches since the malicious queries appear as legitimate database operations.
The underlying technical mechanism involves the improper handling of aggregate functions within the UPDATE statement context during query planning. When PostgreSQL encounters an UPDATE statement containing aggregate functions, the system attempts to optimize the query execution by utilizing MIN/MAX index information. However, the parser fails to properly validate or handle these specific combinations, leading to a crash condition when the optimization routine encounters unexpected data structures or execution paths. This flaw aligns with CWE-472, which addresses external control of code generation, and demonstrates how improper input validation during query analysis can lead to system instability. The vulnerability specifically targets the query analysis phase rather than the execution phase, making it a pre-execution denial of service vector that can be triggered before any actual data modification occurs.
Organizations affected by this vulnerability should implement immediate mitigations including upgrading to PostgreSQL version 8.1.5 or later, which contains the necessary patches to properly handle aggregate functions during UPDATE operations. Additionally, database administrators should consider implementing query monitoring and limiting the privileges of authenticated users to prevent unauthorized exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1499.004, which deals with Network Denial of Service, and T1566.002, which covers Phishing via Social Engineering, as attackers may use this weakness to disrupt database services and potentially gain further access through service interruption. Database security teams should also implement regular patch management processes and conduct vulnerability assessments to identify similar weaknesses in older database versions that may be susceptible to similar exploitation patterns.