CVE-2007-4769 in PostgreSQL
Summary
by MITRE
The regular expression parser in TCL before 8.4.17, as used in PostgreSQL 8.2 before 8.2.6, 8.1 before 8.1.11, 8.0 before 8.0.15, and 7.4 before 7.4.19, allows remote authenticated users to cause a denial of service (backend crash) via an out-of-bounds backref number.
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Analysis
by VulDB Data Team • 07/30/2021
The vulnerability identified as CVE-2007-4769 represents a critical flaw in the regular expression processing capabilities of TCL versions prior to 8.4.17, which was subsequently integrated into various versions of the PostgreSQL database management system. This issue affects PostgreSQL versions 8.2 before 8.2.6, 8.1 before 8.1.11, 8.0 before 8.0.15, and 7.4 before 7.4.19, creating a significant security concern for organizations relying on these database versions. The vulnerability stems from improper handling of backreference numbers within regular expression parsing operations, specifically when encountering out-of-bounds backreference values.
The technical flaw manifests when the TCL regular expression engine processes patterns containing invalid backreference numbers that exceed the bounds of the defined capture groups. This condition occurs during the parsing phase of regular expressions, where the system fails to properly validate the range of backreference identifiers before attempting to resolve them. The vulnerability is particularly dangerous because it allows authenticated remote attackers to craft malicious SQL queries containing specially formatted regular expressions that trigger integer overflow conditions or memory access violations within the TCL parser. When such malformed backreference numbers are encountered, the parser attempts to access memory locations that are either invalid or outside the allocated buffer boundaries, leading to unpredictable behavior and system instability.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as the backend crash can result in complete database service interruption and potential data loss. Attackers exploiting this vulnerability can repeatedly trigger the crash condition, effectively creating a persistent denial of service attack that can severely impact database availability and business continuity. The authentication requirement for exploitation means that only users with valid database credentials can carry out this attack, but this limitation does not mitigate the severity of the impact, as database administrators often maintain elevated privileges and access to sensitive data. This vulnerability aligns with CWE-129, which addresses improper validation of the boundaries of a buffer, and represents a classic example of how regular expression processing can become a vector for system instability.
Organizations affected by this vulnerability should immediately implement mitigations through patching their PostgreSQL installations to versions that include the fixed TCL regular expression parser. The recommended approach involves upgrading to PostgreSQL 8.2.6 or later, 8.1.11 or later, 8.0.15 or later, and 7.4.19 or later, which contain the necessary fixes for the TCL parser. Additionally, administrators should consider implementing input validation measures at the application level to sanitize regular expression inputs and prevent malformed patterns from reaching the database engine. Network-level protections such as firewalls and intrusion detection systems can help monitor for suspicious SQL query patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of maintaining up-to-date software components and highlights how seemingly minor library issues can have cascading effects on critical database infrastructure, potentially aligning with ATT&CK technique T1499.004 for network denial of service attacks. Organizations should also conduct thorough security assessments to identify all systems running vulnerable PostgreSQL versions and establish monitoring procedures to detect potential exploitation attempts.