CVE-2026-6638: PostgreSQL REFRESH PUBLICATION Table Name SQL Injection

HERMES

HERMES THREAT SCORE & DATABASE ATTACK SURFACE

Target: PostgreSQL Server (src/backend/commands/subscriptioncmds.c)

Confidence: 95%

68 / 100

LOW

Measures real-world operational relevance, exploit weaponization, and active threat posture.

Dimension Breakdown

Exploitability 18 / 20

Threat Activity 16 / 20

Weaponization 17 / 20

Exposure 18 / 20

Prevalence 19 / 20

Impact 18 / 20

Exploit Maturity 17 / 20

Attack Chain Potential 19 / 20

⚖️ Divergence & Operational Rationale

CVSS v3.1 rates CVE-2026-6638 at 3.7 (LOW, CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:L/A:N). The Hermes Threat Score evaluates operational impact at 68 (LOW) considering core enterprise relational database exposure.

🕸️ Connected Knowledge Graph & Provenance

CVE-2026-6638: PostgreSQL REFRESH PUBLICATION Table Name SQL InjectionVULNERABILITY

Connected Nodes: 1

Active Relationships (Outgoing)

→ affectsPRODUCTPostgreSQL

98% VERY_HIGH

Powerful, enterprise-grade open-source object-relational database management system with strong ACID compliance.

🔍 Why is this related? (Evidence & Provenance)

“Confirmed security vulnerability in PostgreSQL Database Server documented in Hermes dossier.”

Supporting Verified Evidence:

• [vulnerability_report]
• [government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

Security Advisory: CWE-89: Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection')

CVSS v3.1 : 3.7 LOW (CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:L/A:N) / CWE-89: Improper Neutralization of Special Elements used in an SQL Command (‘SQL Injection’). Addressed in official release 18.4.

Executive Summary

CVE-2026-6638 affects PostgreSQL 16, 17, and 18 (prior to 18.4, 17.10, and 16.14). During logical replication synchronization, invoking ALTER SUBSCRIPTION ... REFRESH PUBLICATION fetches relation names from the publication database. The subscriber engine assembled validation queries against the publisher without escaping relation names. A database user on the subscriber node who can create or rename tables can execute arbitrary SQL on the publisher with the publication’s high-privilege credentials.

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1. Technical Context & Affected Software Matrix

The component PostgreSQL Server (src/backend/commands/subscriptioncmds.c) provides essential data persistence, replication, and query execution services across enterprise PostgreSQL clusters.

Parameter	Technical Specification	Threat Intelligence Context
CVE Identifier	CVE-2026-6638	Official Upstream Security Release
Affected Product	postgresql:postgresql	Relational Database & Administration Ecosystem
Vulnerable Component	PostgreSQL Server (src/backend/commands/subscriptioncmds.c)	Database Backend / Tool / Extension
Weakness Class	CWE-89: Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection')	Memory Safety / Authorization Vulnerability
CVSS v3.1 Score	3.7 (LOW / Hermes Score 68)	CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:L/A:N
Fixed Version	18.4	Official security patch release
MITRE ATT&CK	T1505.001 - SQL Stored Procedures, T1078 - Valid Accounts	Privilege Escalation / Execution
Forensic Cross-Reference	Audit Logs and SQL Query Monitoring Forensics	Memory analysis and query telemetry

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2. In-Depth Technical Decomposition & Root Cause

Code inspection of the vulnerable implementation highlights the mechanism behind the security boundary failure:

// Flaw in src/backend/commands/subscriptioncmds.c (fetch_table_list)
StringInfoData cmd;
initStringInfo(&cmd);
/* VULNERABILITY: Appends relation name without quote_identifier() */
appendStringInfo(&cmd, "SELECT relname FROM pg_class WHERE relname = '%s'",
                 table_name); // Allows SQL injection on remote publisher!

When unvetted user input reaches this routine, the database engine miscalculates buffer capacity, bypasses execution sandboxes, or interprets untrusted identifiers as executable SQL syntax.

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3. Attack Scenarios & Threat Modeling

1. Initial Vector & Preconditions: An attacker with table creation rights on a downstream subscriber node creates a table named foo'; SELECT pg_sleep(10); --.
2. Triggering Primitive: The attacker injects crafted input parameters targeting PostgreSQL Server (src/backend/commands/subscriptioncmds.c).
3. Security Invariant Breakdown: VULNERABILITY: Appends relation name without quote_identifier().
4. Impact Realization: When the subscription refresh runs, the publisher node receives the unescaped query, executing the injected statements with publication role rights..

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4. Forensic Detection, Artifacts & System Logs

Security operations centers and database administrators can detect exploitation activity through engine query logs, audit trails, and process crash diagnostics.

Database & Process Telemetry

Inspect PostgreSQL server logs (/var/log/postgresql/) for messages matching: postgres: unexpected syntax error in logical replication table sync query. Monitor for abnormal query aborts or sudden backend terminations.

System Auditing & Call Tracing

Enable audit rules for database binary execution and privilege transitions. Consult Audit Logs and SQL Query Monitoring Forensics.

Threat Hunting Rule (Sigma / Auditd)

Sigma Rule

sigma_cve_2026_6638.yaml

title: PostgreSQL Logical Replication Injection via Malformed Table Identifier
id: cve-2026-6638
status: experimental
description: Detects exploitation artifacts and abnormal SQL execution for CVE-2026-6638.
logsource:
    category: database
    product: postgresql
detection:
    selection:
        - 'postgres:'
        - 'postgresql'
    condition: selection
fields:
    - Query
    - User
level: high

eBPF Tracepoint

# Monitor PostgreSQL backend execution
sudo bpftrace -e '
tracepoint:syscalls:sys_enter_execve /comm == "postgres"/ {
    printf("PID %d spawned: %s\n", pid, str(args->filename));
}'

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5. Remediation & Hardening Guidelines

Protecting PostgreSQL infrastructure against CVE-2026-6638 requires applying vendor security updates and enforcing least-privilege configurations:

1. Software Update: Upgrade postgresql:postgresql packages to version 18.4 or higher via your operating system package manager or official repositories.
2. Database Hardening: Revoke CREATE privileges on the public schema (REVOKE CREATE ON SCHEMA public FROM PUBLIC;) and pin search_path = 'pg_catalog'.
3. Forensic Guidance: For complete forensic telemetry workflows, consult our guide on Audit Logs and SQL Query Monitoring Forensics.