CVE-2020-25695: PostgreSQL SQL Injection Vulnerability

CVE-2020-25695 Overview

A critical privilege escalation flaw was discovered in PostgreSQL versions before 13.1, 12.5, 11.10, 10.15, 9.6.20, and 9.5.24. This vulnerability allows an attacker with permission to create non-temporary objects in at least one schema to execute arbitrary SQL functions under the identity of a superuser. The exploitation of this flaw poses severe threats to data confidentiality, integrity, and overall system availability.

Critical Impact

Attackers can escalate privileges to superuser level and execute arbitrary SQL functions, potentially compromising the entire database system including sensitive data exfiltration, data manipulation, and service disruption.

Affected Products

• PostgreSQL versions before 13.1
• PostgreSQL versions before 12.5, 11.10, 10.15, 9.6.20, and 9.5.24
• Debian Linux 9.0

Discovery Timeline

• November 16, 2020 - CVE-2020-25695 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-25695

Vulnerability Analysis

This vulnerability stems from improper privilege handling within PostgreSQL's object creation and function execution mechanisms. When a user has permission to create non-temporary objects within at least one schema, they can craft malicious database objects that, when processed by the database engine, execute under the elevated privileges of a superuser context.

The flaw is classified under CWE-89 (SQL Injection), indicating that the vulnerability involves improper neutralization of special elements used in SQL commands. An attacker can leverage legitimate database functionality in an unintended manner to bypass normal access controls and assume superuser privileges.

The attack requires network access and low privileges (the ability to create objects in a schema), but requires no user interaction. Once exploited, the attacker gains complete control over database operations, enabling unauthorized access to all data, modification of database structures, and potential denial of service through destructive operations.

Root Cause

The root cause lies in PostgreSQL's handling of object ownership and privilege inheritance during SQL function execution. The database fails to properly validate and maintain privilege boundaries when certain database objects are created and subsequently referenced by system processes running under superuser context. This allows crafted objects to hijack the elevated execution context.

Attack Vector

The attack is network-accessible and can be executed by any authenticated user who has been granted the CREATE privilege on at least one schema. The attacker creates specially crafted database objects (such as functions, views, or operators) within their accessible schema. When these objects are subsequently accessed or processed by system operations running with superuser privileges, the malicious code executes in the superuser context.

The exploitation mechanism involves creating database objects that will be invoked during system operations such as autovacuum, ANALYZE, or other maintenance tasks that run with elevated privileges. This allows the attacker to effectively "trap" superuser operations and redirect them to execute attacker-controlled SQL code.

Detection Methods for CVE-2020-25695

Indicators of Compromise

• Unexpected or unauthorized database objects (functions, views, operators) created by non-privileged users
• Unusual SQL function executions logged under superuser identity that don't match expected administrative activities
• New roles with elevated privileges created without administrator authorization
• Database audit logs showing privilege escalation patterns or unauthorized data access

Detection Strategies

• Enable PostgreSQL logging parameters log_statement = 'all' and log_connections = on to capture comprehensive query and connection activity
• Monitor pg_stat_activity for suspicious queries executing under superuser context from unexpected sources
• Implement role-based audit triggers on system catalogs like pg_proc, pg_class, and pg_namespace to detect unauthorized object creation
• Use database activity monitoring solutions to detect anomalous privilege escalation patterns

Monitoring Recommendations

• Configure alerts for creation of new functions, views, or operators by non-administrative users
• Monitor for unusual autovacuum or maintenance operation failures that may indicate exploitation attempts
• Regularly audit schema permissions to identify users with unnecessary CREATE privileges
• Review pg_roles periodically for unexpected superuser memberships or privilege grants

How to Mitigate CVE-2020-25695

Immediate Actions Required

• Upgrade PostgreSQL immediately to patched versions: 13.1, 12.5, 11.10, 10.15, 9.6.20, or 9.5.24 or later
• Audit all schemas and revoke CREATE privileges from users who do not require them
• Review recently created database objects for any suspicious functions, views, or operators
• Enable comprehensive database logging to establish audit trails

Patch Information

PostgreSQL has released security updates addressing this vulnerability. Organizations should upgrade to the following minimum versions: PostgreSQL 13.1, 12.5, 11.10, 10.15, 9.6.20, or 9.5.24. Detailed patch information and release notes are available through the PostgreSQL Security Support Information page. Linux distribution users should also apply updates from their respective vendors, including Debian LTS Advisory December 2020 and Gentoo GLSA 202012-07.

Workarounds

• Restrict CREATE privileges to only essential administrative accounts until patches can be applied
• Implement strict schema isolation by preventing regular users from creating objects in shared schemas
• Use search_path hardening by explicitly setting secure search paths for superuser functions
• Consider temporarily disabling autovacuum on untrusted schemas if patching is delayed (note: this impacts performance)

# Revoke CREATE privileges from public schema for all users
psql -c "REVOKE CREATE ON SCHEMA public FROM PUBLIC;"

# Review users with CREATE privileges on any schema
psql -c "SELECT grantee, table_schema, privilege_type FROM information_schema.schema_privileges WHERE privilege_type = 'CREATE';"

# Enable comprehensive logging for security monitoring
# Add to postgresql.conf:
# log_statement = 'all'
# log_connections = on
# log_disconnections = on