Summary
elFinder unsafe upload filtering leading to remote code execution
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.
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).
The application accepts file uploads without adequately restricting the file type or content. Typical impact: remote code execution if the uploaded file can be served and executed on the server.
CVE-2021-23394 has a CVSS score of 8.1 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.1.58); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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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.
Frequently Asked Questions
- What is CVE-2021-23394? CVE-2021-23394 is a high-severity unrestricted upload of dangerous file types vulnerability in studio-42/elfinder (composer), affecting versions < 2.1.58. It is fixed in 2.1.58. The application accepts file uploads without adequately restricting the file type or content.
- How severe is CVE-2021-23394? CVE-2021-23394 has a CVSS score of 8.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of studio-42/elfinder are affected by CVE-2021-23394? studio-42/elfinder (composer) versions < 2.1.58 is affected.
- Is there a fix for CVE-2021-23394? Yes. CVE-2021-23394 is fixed in 2.1.58. Upgrade to this version or later.
- Is CVE-2021-23394 exploitable, and should I be worried? Whether CVE-2021-23394 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2021-23394 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2021-23394? Upgrade
studio-42/elfinderto 2.1.58 or later.