CVE-2020-25696: PostgreSQL psql Terminal RCE Vulnerability

CVE-2020-25696 Overview

A flaw was found in the psql interactive terminal of PostgreSQL that allows arbitrary code execution when a user connects to a compromised server. The vulnerability exists in multiple PostgreSQL versions before 13.1, 12.5, 11.10, 10.15, 9.6.20, and 9.5.24. When an interactive psql session uses the \gset meta-command while querying a malicious or compromised server, an attacker can execute arbitrary code as the operating system account running the psql client.

Critical Impact

Attackers controlling a compromised PostgreSQL server can achieve arbitrary code execution on client systems using the psql interactive terminal, threatening data confidentiality, integrity, and system availability.

Affected Products

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

Discovery Timeline

• 2020-11-23 - CVE-2020-25696 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-25696

Vulnerability Analysis

This vulnerability (CWE-183: Permissive List of Allowed Inputs, CWE-697: Incorrect Comparison) exists in the psql interactive terminal's handling of the \gset meta-command. The \gset command is designed to store query results as psql variables, which can then be used in subsequent commands or scripts. The flaw occurs because psql does not properly validate or sanitize server-controlled values before using them in contexts that could lead to code execution.

When a user connects to a malicious PostgreSQL server and issues a query using \gset, the server can return specially crafted data that, when processed by psql, results in arbitrary command execution. This is particularly dangerous in scenarios where users may connect to untrusted servers or in environments where a legitimate server has been compromised.

The attack requires network access and user interaction (the victim must execute a query with \gset against the malicious server), but once these conditions are met, full code execution is achieved with the privileges of the user running psql.

Root Cause

The root cause of this vulnerability is inadequate input validation in the psql client when processing server responses during \gset operations. The psql terminal allows variable assignment from query results without properly restricting what characters or escape sequences can be included in the values. This creates a permissive input handling scenario where attacker-controlled data from the server can influence client-side execution.

The vulnerability is classified under CWE-183 (Permissive List of Allowed Inputs) and CWE-697 (Incorrect Comparison), indicating that the input validation mechanisms were insufficient to prevent malicious payloads from being processed as executable content.

Attack Vector

The attack vector is network-based and requires the following conditions:

1. The attacker must control or have compromised a PostgreSQL server
2. A victim must connect to this malicious server using the psql interactive terminal
3. The victim must execute a query using the \gset meta-command

The malicious server responds to the \gset query with specially crafted data containing escape sequences or shell metacharacters. When psql processes these values and assigns them to variables, the malicious content can be executed as operating system commands. This allows the attacker to run arbitrary code with the privileges of the user account running the psql client, potentially leading to complete system compromise.

The attack does not require any authentication on the attacker's part beyond controlling the server, and it exploits the trust relationship between the psql client and the server it connects to.

Detection Methods for CVE-2020-25696

Indicators of Compromise

• Unusual outbound connections from psql client processes to unknown or suspicious PostgreSQL servers
• Unexpected process spawning from psql sessions, particularly shell processes or command interpreters
• Anomalous system calls or file operations initiated by psql processes
• Evidence of shell command execution in psql session logs or command history

Detection Strategies

• Monitor network traffic for psql connections to non-approved or external PostgreSQL servers
• Implement endpoint detection rules to alert on child process creation from psql binaries
• Review psql command history files for suspicious \gset usage patterns
• Deploy behavioral analysis to detect psql processes executing unexpected system commands

Monitoring Recommendations

• Enable comprehensive logging of psql sessions and database connections
• Configure network monitoring to track all PostgreSQL protocol traffic (port 5432)
• Implement file integrity monitoring on systems where psql is frequently used
• Establish baseline behavior patterns for psql usage and alert on deviations

How to Mitigate CVE-2020-25696

Immediate Actions Required

• Upgrade PostgreSQL to patched versions: 13.1, 12.5, 11.10, 10.15, 9.6.20, or 9.5.24 immediately
• Restrict psql client connections to only trusted, known PostgreSQL servers
• Implement network segmentation to limit exposure of psql clients to untrusted networks
• Educate users about the risks of connecting to untrusted database servers

Patch Information

PostgreSQL has released security updates addressing this vulnerability across all supported versions. The PostgreSQL Release Announcement provides details on the patched releases: PostgreSQL 13.1, 12.5, 11.10, 10.15, 9.6.20, and 9.5.24. Organizations should upgrade to these versions or later to remediate this vulnerability. Additional vendor information is available in the Red Hat Bug Report #1894430. Debian users should refer to the Debian LTS Announcement December 2020, and Gentoo users should consult Gentoo GLSA 202012-07.

Workarounds

• Avoid using \gset commands when connected to untrusted or unknown PostgreSQL servers
• Use read-only connections and restrict interactive psql usage in production environments
• Implement strict network access controls to prevent psql clients from connecting to unauthorized servers
• Consider using connection poolers or proxy solutions that can inspect and filter PostgreSQL traffic

# Configuration example - Restrict PostgreSQL client connections
# In pg_hba.conf on trusted servers, ensure only known hosts can connect
# Additionally, configure firewall rules to limit outbound connections

# Example iptables rule to restrict psql outbound connections
iptables -A OUTPUT -p tcp --dport 5432 -d trusted_server_ip -j ACCEPT
iptables -A OUTPUT -p tcp --dport 5432 -j DROP