CVE-2026-18893 in CockroachDB PostgreSQL for VPC
Summary
by MITRE • 11/08/2026
IBM CockroachDB PostgreSQL for IBM VPC 26.2.0 through 26.2.3, 25.4.0 through 25.4.12, and 25.2.0 through 25.2.20 is vulnerable to privilege escalation via user-defined function.
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Analysis
by VulDB Data Team • 11/08/2026
The vulnerability identified in IBM CockroachDB PostgreSQL for IBM VPC versions ranging from 26.2.0 through 26.2.3, as well as the 25.x series updates up to 25.4.12 and 25.2.20, represents a critical security flaw centered on privilege escalation via user-defined functions. This issue arises within the database engine's execution environment for custom scripts written by application developers or administrators. User-defined functions allow users to extend the functionality of the database system by defining their own logic in languages such as PL/pgSQL, Python, or other supported procedural extensions. While this feature is essential for complex data processing and business logic implementation, it introduces a significant attack surface if not properly isolated from core system privileges.
The technical root cause lies in how the database engine handles permission checks during the execution of these custom functions. In vulnerable versions, the privilege verification mechanism fails to correctly enforce least-privilege principles when invoking internal procedures or accessing sensitive system catalogs through user-defined code. An attacker with access to create and execute user-defined functions can craft a malicious function that exploits this oversight. By leveraging specific API calls or internal hooks within the database engine, the crafted function can bypass standard authentication and authorization layers. This allows the function to operate under elevated privileges, effectively granting the low-privileged user administrative control over the database instance.
From an operational perspective, this vulnerability poses a severe risk to data integrity and availability. Once privilege escalation is achieved, the attacker gains unrestricted access to all databases hosted on the affected server. They can read, modify, or delete sensitive information across multiple tenants if multi-tenancy is enabled. Furthermore, the ability to execute arbitrary code with high privileges may allow for lateral movement within the underlying infrastructure hosting IBM VPC services. The impact extends beyond data theft; attackers could disrupt service availability by dropping critical tables, altering configuration settings, or installing backdoors that persist even after initial access is detected. This aligns closely with CWE-269, which describes Improper Privilege Management, and specifically relates to the exploitation of software components that fail to enforce proper separation between user-level operations and system-level administrative tasks.
The attack vector for this vulnerability typically involves an authenticated low-privileged database user who has been granted permission to create functions or procedures. This is a common configuration in development environments but can persist into production if access controls are not strictly audited. The attacker would write a function containing malicious logic designed to trigger the privilege escalation flaw, then execute that function within their session. Upon execution, the database engine incorrectly elevates the security context of the current transaction or connection. This behavior is consistent with ATT&CK technique T1078, Valid Accounts, where attackers leverage legitimate credentials and system features to gain higher-level access without triggering immediate alarms associated with brute-force attacks or external exploitation tools.
Mitigation strategies must focus on both patching and architectural hardening. The primary remediation step is to apply the latest security updates provided by IBM for CockroachDB PostgreSQL in VPC environments, ensuring that all instances are updated beyond version 26.2.3, 25.4.12, or 25.2.20 depending on the specific branch being used. Organizations should also review their database access policies to restrict who can create user-defined functions. Implementing strict role-based access control ensures that only trusted administrators have the ability to define procedural code. Additionally, enabling detailed audit logging for function creation and execution events allows security teams to detect anomalous behavior indicative of exploitation attempts. Regular vulnerability scanning and penetration testing focused on database interfaces are recommended to identify misconfigurations before they can be exploited by malicious actors seeking to compromise cloud-based data assets.