CVE-2025-4207: PostgreSQL GB18030 DoS Vulnerability

CVE-2025-4207 Overview

A buffer over-read vulnerability has been identified in PostgreSQL's GB18030 encoding validation mechanism. This flaw allows a database input provider to trigger a temporary denial of service condition on platforms where a 1-byte over-read can cause process termination. The vulnerability affects both the PostgreSQL database server and the libpq client library, potentially impacting database availability for organizations relying on PostgreSQL infrastructure.

Critical Impact

Database servers and client applications using libpq may experience unexpected termination when processing maliciously crafted GB18030-encoded input, leading to service disruption.

Affected Products

• PostgreSQL versions before 17.5
• PostgreSQL versions before 16.9
• PostgreSQL versions before 15.13
• PostgreSQL versions before 14.18
• PostgreSQL versions before 13.21
• libpq client library (versions corresponding to affected PostgreSQL releases)

Discovery Timeline

• May 8, 2025 - CVE-2025-4207 published to NVD
• May 12, 2025 - Last updated in NVD database

Technical Details for CVE-2025-4207

Vulnerability Analysis

This vulnerability stems from improper boundary checking during GB18030 character encoding validation within PostgreSQL. GB18030 is a Chinese character encoding standard that uses variable-length byte sequences (1, 2, or 4 bytes per character). The encoding validation logic fails to properly verify buffer boundaries before reading character data, resulting in an out-of-bounds read condition.

When the validation function processes input near the end of a buffer, it may attempt to read one byte beyond the allocated memory region. On platforms with strict memory protection (such as those using guard pages or address sanitization), this 1-byte over-read can trigger a segmentation fault or similar memory access violation, causing immediate process termination.

The vulnerability is classified under CWE-126 (Buffer Over-read), which describes conditions where software reads data past the end of an intended buffer. While this particular over-read does not lead to information disclosure, it creates a denial of service vector that can disrupt database operations.

Root Cause

The root cause lies in insufficient bounds checking within the GB18030 encoding validation routines. When processing multi-byte character sequences, the validation code does not adequately verify that the complete character sequence fits within the input buffer before attempting to read all required bytes. This oversight allows a carefully crafted input to trigger a read operation that extends one byte past the buffer boundary.

Attack Vector

An attacker with the ability to supply input to a PostgreSQL database can exploit this vulnerability by providing specially crafted GB18030-encoded data. The attack requires network access to submit malicious input, though the high attack complexity stems from platform-specific behavior—the vulnerability only causes denial of service on platforms where out-of-bounds memory reads result in process termination.

Attack scenarios include:

• Submitting malformed GB18030-encoded strings through SQL queries
• Providing crafted data through application interfaces that connect via libpq
• Exploiting data import functionality that processes GB18030-encoded content

The vulnerability affects both server-side processing (PostgreSQL daemon) and client-side applications using the libpq library, expanding the potential attack surface.

Detection Methods for CVE-2025-4207

Indicators of Compromise

• Unexpected PostgreSQL server process crashes or restarts
• libpq-based client applications terminating unexpectedly when processing certain data
• Segmentation fault entries in system logs associated with PostgreSQL processes
• Increased frequency of database connection failures or timeouts

Detection Strategies

• Monitor PostgreSQL server logs for abnormal termination events and segmentation faults
• Implement application-level logging to track input processing failures, particularly for GB18030-encoded data
• Deploy memory error detection tools (e.g., AddressSanitizer) in development and staging environments to identify over-read conditions
• Use intrusion detection systems to flag unusual patterns of database connection failures

Monitoring Recommendations

• Configure alerting for PostgreSQL service availability and unexpected restarts
• Monitor system logs for memory access violations related to database processes
• Track database connection pool health and failure rates for anomalies
• Implement synthetic monitoring to detect database availability issues

How to Mitigate CVE-2025-4207

Immediate Actions Required

• Upgrade PostgreSQL to patched versions: 17.5, 16.9, 15.13, 14.18, or 13.21
• Review and update all applications using libpq to ensure they link against patched library versions
• Implement input validation at the application layer to sanitize encoding-related data before database submission
• Consider temporarily restricting GB18030 encoding usage if immediate patching is not feasible

Patch Information

PostgreSQL has released security updates addressing this vulnerability across all supported version branches. Organizations should upgrade to the following minimum versions:

For detailed patch information and upgrade instructions, refer to the PostgreSQL Security Advisory. Additional distribution-specific guidance is available in the Debian LTS Security Announcement.

Workarounds

• If immediate patching is not possible, consider implementing application-level input filtering for GB18030-encoded data
• Deploy database connection pooling with automatic reconnection to minimize service disruption from potential crashes
• Monitor and limit access to database interfaces that accept GB18030-encoded input
• Use network segmentation to restrict database access to trusted application servers only

# Check current PostgreSQL version
psql --version

# For Debian/Ubuntu systems, update PostgreSQL
sudo apt update
sudo apt upgrade postgresql

# Verify the installed version is patched
psql -c "SELECT version();"