CVE-2021-20028: SonicWall SMA 210 SQL Injection Flaw

CVE-2021-20028 Overview

CVE-2021-20028 is a SQL Injection vulnerability affecting SonicWall Secure Remote Access (SRA) products that have reached end-of-life status. The vulnerability stems from improper neutralization of SQL commands in the SRA appliances running all 8.x firmware versions and 9.0.0.9-26sv or earlier. This flaw allows unauthenticated remote attackers to inject malicious SQL commands, potentially leading to complete compromise of the affected systems.

Critical Impact

This vulnerability is actively exploited in the wild and has been added to the CISA Known Exploited Vulnerabilities catalog. Unauthenticated attackers can remotely exploit this SQL injection flaw to gain unauthorized access to sensitive data, modify database contents, and potentially achieve full system compromise.

Affected Products

• SonicWall SMA 210 (all 8.x firmware and 9.0.0.9-26sv or earlier)
• SonicWall SMA 410 (all 8.x firmware and 9.0.0.9-26sv or earlier)
• SonicWall SMA 500v (all 8.x firmware and 9.0.0.9-26sv or earlier)
• SonicWall SRA 4600 (all 8.x firmware and 9.0.0.9-26sv or earlier)
• SonicWall SRA 1600 (all 8.x firmware and 9.0.0.9-26sv or earlier)
• SonicWall SRA VA (all 8.x firmware and 9.0.0.9-26sv or earlier)

Discovery Timeline

• 2021-08-04 - CVE-2021-20028 published to NVD
• 2025-10-31 - Last updated in NVD database

Technical Details for CVE-2021-20028

Vulnerability Analysis

This SQL Injection vulnerability (CWE-89) occurs due to improper neutralization of special elements used in SQL commands within the SonicWall SRA web interface. The affected appliances fail to properly sanitize user-supplied input before incorporating it into SQL queries, allowing attackers to manipulate database operations.

The vulnerability is particularly dangerous because it requires no authentication to exploit, making it accessible to any attacker with network access to the vulnerable appliance. Successful exploitation can result in unauthorized access to sensitive data stored in the backend database, including user credentials, session tokens, and configuration information. Additionally, attackers may be able to modify or delete database records, potentially disrupting operations or creating persistent backdoors.

Given that these are end-of-life products, organizations using affected devices face significant risk as continued security support is limited.

Root Cause

The root cause of CVE-2021-20028 is the failure to implement proper input validation and parameterized queries in the SRA firmware. User-controlled input is directly concatenated into SQL statements without adequate sanitization, allowing attackers to break out of the intended query context and inject arbitrary SQL commands. This classic SQL injection vulnerability pattern enables attackers to execute unauthorized database operations.

Attack Vector

The attack vector is network-based, requiring no privileges or user interaction. An attacker can exploit this vulnerability by sending specially crafted HTTP requests to the SRA appliance's web interface. The malicious SQL payload is embedded within user-controllable input fields that are subsequently processed by vulnerable backend code.

The SQL injection can be leveraged to:

• Extract sensitive information from the database (data exfiltration)
• Bypass authentication mechanisms
• Modify or delete critical data
• Potentially escalate to remote code execution depending on database configuration

Due to the nature of remote access appliances being internet-facing, exposed devices are particularly susceptible to opportunistic attacks.

Detection Methods for CVE-2021-20028

Indicators of Compromise

• Unusual SQL error messages appearing in web application logs or responses
• Anomalous database queries containing SQL keywords like UNION, SELECT, OR 1=1, --, or encoded variants
• Unexpected authentication bypasses or unauthorized access to administrative functions
• Database log entries showing query manipulation attempts

Detection Strategies

• Deploy web application firewalls (WAF) with SQL injection detection rules targeting SonicWall SRA traffic patterns
• Implement network intrusion detection signatures for known SQL injection attack payloads
• Monitor authentication logs for suspicious login patterns or unexpected privilege escalation
• Analyze HTTP request logs for anomalous parameters containing SQL metacharacters

Monitoring Recommendations

• Enable detailed logging on SonicWall SRA appliances and forward logs to a SIEM for centralized analysis
• Configure alerts for repeated failed authentication attempts followed by successful logins
• Monitor outbound network connections from the SRA appliance for potential data exfiltration
• Review database audit logs for unauthorized query patterns or bulk data access

How to Mitigate CVE-2021-20028

Immediate Actions Required

• Identify all SonicWall SRA appliances in your environment running vulnerable firmware versions (8.x or 9.0.0.9-26sv and earlier)
• Since affected products are end-of-life, immediately plan for replacement with supported alternatives such as SonicWall SMA 100 or SMA 1000 series
• If immediate replacement is not possible, isolate affected appliances from direct internet exposure using network segmentation
• Implement additional security controls such as IP allowlisting and VPN access requirements

Patch Information

As the affected SonicWall SRA products have reached end-of-life status, security patches may not be available. SonicWall recommends migrating to supported product lines. Organizations should consult the SonicWall Vulnerability Advisory (SNWLID-2021-0017) for detailed guidance on remediation options and supported upgrade paths.

For additional context on the active exploitation of this vulnerability, refer to the CISA Known Exploited Vulnerabilities Catalog.

Workarounds

• Restrict network access to the SRA management interface to trusted IP addresses only
• Place the SRA appliance behind a WAF configured to block SQL injection attempts
• Disable any unnecessary services or features on the appliance to reduce attack surface
• Implement network-level access controls to limit who can reach the vulnerable endpoints

# Network access restriction example (firewall rule)
# Block direct internet access to SRA appliance, allow only from trusted management network
iptables -A INPUT -p tcp --dport 443 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP