CVE-2016-2193 in PostgreSQL
Summary
by MITRE
PostgreSQL before 9.5.x before 9.5.2 does not properly maintain row-security status in cached plans, which might allow attackers to bypass intended access restrictions by leveraging a session that performs queries as more than one role.
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Analysis
by VulDB Data Team • 07/12/2022
PostgreSQL versions prior to 9.5.2 contain a critical row-level security vulnerability that stems from improper handling of cached execution plans. This flaw exists in the query planner's caching mechanism where the system fails to correctly track row-security status when reusing previously prepared execution paths. The vulnerability specifically affects scenarios where database sessions perform queries under multiple roles or privileges, creating a condition where cached plans retain outdated security contexts that do not reflect current user permissions. This technical weakness allows malicious actors to exploit the cached plan state to access data that should normally be restricted based on row-level security policies. The flaw operates at the intersection of query optimization and access control mechanisms, where the planner's caching logic does not adequately invalidate or update security-related metadata when transitioning between different user roles within the same session. This creates a persistent security boundary violation that can be leveraged across multiple queries executed within the same database session, potentially enabling unauthorized data access through privilege escalation.
The operational impact of this vulnerability extends beyond simple data exposure to encompass potential privilege escalation and unauthorized data manipulation. Attackers can exploit this weakness by establishing a database session that initially operates under one role with specific row-level security permissions, then subsequently executing queries that should be restricted under different security contexts. The cached plan maintains the original security state information, allowing the attacker to bypass intended access controls that would normally prevent data access based on row-level security policies. This vulnerability particularly affects systems that rely heavily on role-based access control and row-level security features, where users may need to switch between different privilege levels within a single session. The attack vector is most effective when the target database session contains a mix of administrative and restricted user roles, enabling the exploitation of the cached plan state to access data that should be logically restricted under different security contexts. This issue represents a fundamental flaw in PostgreSQL's security model implementation where the optimization benefits of query plan caching are achieved at the expense of proper access control enforcement.
Mitigation strategies for CVE-2016-2193 should focus on immediate version upgrades to PostgreSQL 9.5.2 or later, which contain the necessary patches to properly handle row-security status in cached execution plans. Organizations should implement comprehensive monitoring of database sessions to detect unusual role switching patterns that might indicate exploitation attempts. The recommended approach includes disabling prepared statements or query plan caching for security-sensitive operations where role transitions occur, though this may impact performance. Database administrators should also review and audit existing row-level security policies to ensure proper implementation and test scenarios that involve multiple role usage within single sessions. Security hardening measures should include regular patch management processes that prioritize PostgreSQL security updates, particularly those addressing query planning and access control components. Additionally, implementing network-level controls and database activity monitoring can help detect anomalous behavior patterns associated with privilege escalation attempts. This vulnerability aligns with CWE-284 Access Control Issues and can be mapped to ATT&CK technique T1078 Valid Accounts, as exploitation typically involves leveraging legitimate database sessions with appropriate privileges to bypass security controls through plan caching mechanisms. Organizations should also consider implementing database auditing and logging to track role transitions and query execution patterns that could indicate exploitation attempts. The fix addresses the underlying architectural flaw by ensuring that cached execution plans properly invalidate or refresh their security context information when role changes occur within database sessions, thereby maintaining the integrity of row-level security policies.