How severe is CVE-2021-23394?

CVE-2021-23394 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-23394?

CVE-2021-23394 affects the following packages: studio-42/elfinder (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2021-23394?

Update studio-42/elfinder to 2.1.58 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23394 is resolved across your whole dependency graph.

How do I detect CVE-2021-23394 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for studio-42/elfinder, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-23394 if there is no patch (or I can't update yet)?

Treat uploaded files as untrusted until proven otherwise: validate the actual content type rather than the supplied extension, store uploads outside the web root on a volume mounted without execute permission, and rename them to server-generated identifiers so an attacker cannot choose the path a request will later resolve.

Is CVE-2021-23394 actively exploited in the wild?

Yes. There are 2 known exploit references for CVE-2021-23394, including 2 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-23394?

CVE-2021-23394 has an EPSS (Exploit Prediction Scoring System) score of 18.9%, placing it in the 97th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score warrants monitoring and prompt remediation.

What type of vulnerability is CVE-2021-23394?

CVE-2021-23394 is classified as Unrestricted File Upload (CWE-434). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

Is there exploit tooling available for CVE-2021-23394?

A Nuclei detection template exists for CVE-2021-23394, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2021-23394 published, and has it been updated?

CVE-2021-23394 was published on June 13, 2021 and was last updated on August 7, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘

🐘 Packagist

Not in CISA KEV

CRITICAL severity

CVE-2021-23394 — elfinder

CRITICALFix: Studio-42/elFinder@75ea92d

CVE-2021-23394 is a critical-severity (CVSS 9.8) Unrestricted File Upload vulnerability in studio-42/elfinder. 2 public exploit references exist, so weaponization risk is real. A fix is available for studio-42/elfinder — see the affected versions and patch details below.

elFinder unsafe upload filtering leading to remote code execution

Also known asGHSA-qm58-cvvm-c5qrSNYK-PHP-STUDIO42ELFINDER-1290554

Published

Jun 13, 2021

Updated

Aug 7, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

2 known

Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

18.9%probability of exploitation in next 30 days

Moderate Risk0.00%

Lower risk than most CVEs97th percentile — riskier than 97% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-23394 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐘studio-42/elfinder

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

Impact

Before elFinder 2.1.58, the upload filter did not disallow the upload of .phar files. As several Linux distributions are now shipping Apache configured in a way it will process these files as PHP scripts, attackers could gain arbitrary code execution on the server hosting the PHP connector (even in minimal configuration).

Patches

The issue has been addressed with https://github.com/Studio-42/elFinder/commit/75ea92decc16a5daf7f618f85dc621d1b534b5e1, associating .phar files to the right MIME type. Unless explicitly allowed in the configuration, such files cannot be uploaded anymore. This patch is part of the last release of elFinder, 2.1.58.

Workarounds

If you can't update to 2.1.58, make sure your connector is not exposed without authentication.

Important tips

Server-side scripts can often be created as text files. Currently, elFinder has an appropriate MIME type set for file extensions that are generally runnable on a web server.

However, the server has various settings. In some cases, the executable file may be judged as "text/plain". Therefore, elFinder installers should understand the extensions that can be executed on the web server where elFinder is installed, and check if there are any missing items in the elFinder settings.

The elFinder PHP connector has an option "additionalMimeMap" that specifies the MIME type for each extension. See #3295(comment) for more information.

References

https://snyk.io/vuln/composer:studio-42%2Felfinder
https://github.com/Studio-42/elFinder/issues/3295
Further technical details will be disclosed on https://blog.sonarsource.com/tag/security after some time.

For more information

If you have any questions or comments about this advisory, you can contact:

The original reporters, by sending an email to support [at] snyk.io or vulnerability.research [at] sonarsource.com;
The maintainers, by opening an issue on this repository.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`studio-42/elfinder`	all versions	2.1.58`composer require studio-42/elfinder:^2.1.58`

Affected Products

1 product · 1 configurations

Application

elfinderstd42

< 2.1.58

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

The package studio-42/elfinder before 2.1.58 are vulnerable to Remote Co…

github.comNVDJun 2021

The package studio-42/elfinder before 2.1.58 are vulnerable to Remote Co…

blog.sonarsource.comNVDNov 2022

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for studio-42/elfinder, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update studio-42/elfinder to 2.1.58 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23394 is resolved across your whole dependency graph.
Workarounds
Treat uploaded files as untrusted until proven otherwise: validate the actual content type rather than the supplied extension, store uploads outside the web root on a volume mounted without execute permission, and rename them to server-generated identifiers so an attacker cannot choose the path a request will later resolve.

How to detect CVE-2021-23394

A community-maintained Nuclei template exists for this CVE. You can scan for it directly:

nuclei -id cve-2021-23394 -u https://target

Template: elFinder < 2.1.58 - Remote Code Execution
Severity: high
Impact: Attackers can execute arbitrary PHP code on the server, potentially leading to full server compromise.
Remediation: Update to version 2.1.58 or later.

Template by ProjectDiscovery nuclei-templates (0xanis), MIT licensed. View the full template. Scan only systems you are authorised to test.

Frequently Asked Questions

### Impact Before elFinder 2.1.58, the upload filter did not disallow the upload of `.phar` files. As several Linux distributions are now shipping Apache configured in a way it will process these files as PHP scripts, attackers could gain arbitrary code execution on the server hosting the PHP connector (even in minimal configuration). ### Patches The issue has been addressed with https://github.com/Studio-42/elFinder/commit/75ea92decc16a5daf7f618f85dc621d1b534b5e1, associating `.phar` files to the right MIME type. Unless explicitly allowed in the configuration, such files cannot be uploaded