SonicWall Email Security Arbitrary Admin Account Creation Vulnerability (CVE-2021-20021) Security Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTOn-premises and virtual appliance deployments of SonicWall Email Security running version 10.0.9.x.
Unauthenticated remote attackers can create administrative accounts by sending crafted HTTP requests, leading to full system compromise.
Immediately upgrade to the patched firmware version (10.0.9.6173, 10.0.10, or higher).
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Administrators must download and apply the latest firmware patch (10.0.9.6173 or 10.0.10 and above) from the SonicWall portal. Below is an example of verifying system status via CLI:
# 1. Check current system version and status
show system status
# 2. Apply the official firmware upgrade via CLI or Web UI
# (Ensure a full configuration backup is taken prior to upgrading)
upgrade system firmware-image2. Temporary Workaround & Hardening Configuration
If patching cannot be applied immediately, restrict access to the web management interface using firewall rules or Access Control Lists (ACLs) to allow only trusted administrative IP ranges.
# Example: Restrict access to port 443 to a specific management subnet and drop all other traffic
iptables -A INPUT -p tcp -s 192.168.10.0/24 --dport 443 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP3. Log Audit & IoC Verification Commands
Inspect web server access logs and system audit logs for unauthorized administrative account creation attempts.
# Search web access logs for suspicious POST requests targeting user creation endpoints
grep -Ei 'add.*user|create.*admin|user.*management' /var/log/sonicwall/httpd_access.log
# Audit local system accounts and check for recently created administrative users
cat /etc/passwd | grep -E 'admin|root'
lastlogStop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
Eliminate public-facing VPN concentrators and firewall management ports with identity-first Zero-Trust Network Access.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2021-20021) is an improper privilege management flaw (CWE-269) in the web management interface of SonicWall Email Security. The root cause lies in the application's failure to properly validate and authorize incoming HTTP API requests for administrative actions. This allows an attacker to bypass authentication filters and directly access account creation endpoints.
2. Exploitation Mechanics & Attack Scenario
An attacker scans for publicly accessible SonicWall Email Security management interfaces (typically on TCP ports 80 or 443). By crafting a specific HTTP POST request containing parameters for a new user account with administrative privileges, the attacker bypasses the authentication layer. The server processes the unauthorized request and registers the new administrator account, granting the attacker full administrative access.
3. Infrastructure & Business Impact
With a CVSS score of 9.8 and active exploitation confirmed by its inclusion in the CISA KEV catalog, this vulnerability poses an extreme risk. Successful exploitation allows attackers to intercept sensitive email archives, alter mail routing rules for Business Email Compromise (BEC) campaigns, and establish a persistent foothold within the corporate network.
Official Vendor Advisories & References
A vulnerability in the SonicWall Email Security version 10.0.9.x allows an attacker to create an administrative account by sending a crafted HTTP request to the remote host.
Frequently Asked SecOps Questions (CVE-2021-20021)
FAQQ1. How critical is CVE-2021-20021 and is it actively exploited in the wild?
CVE-2021-20021 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 88.8%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2021-20021?
Primary impacted vendors include sonicwall across email security. Scope summary: All SonicWall Email Security versions 10.0.9.x
Q3. What temporary mitigations or workarounds exist for CVE-2021-20021 before patching?
[Mitigation] Immediately upgrade to the patched firmware version (10.0.9.6173, 10.0.10, or higher). Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2021-20021
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