External risk intelligence

Arbitrary File Upload in PHP Upload Class and Joomla K2 Component.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2019-19634

This is a vulnerability in a PHP file upload library (class.upload.php) widely used within web applications and content management systems like Joomla! K2. Because it is a core component for handling user-submitted files in public-facing web applications, it is commonly deployed in internet-accessible environments where web forms are exposed to the public.

Unrestricted File Upload

Verot Project Verot

before 1.0.32.0.0 to before 2.0.42.10.1 and earlier

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This vulnerability impacts a file upload component used in various web applications, allowing for arbitrary file uploads that could lead to system compromise. While the specific impact depends on how the affected component is implemented and utilized, it represents a critical security risk.

Allows uploading dangerous files.
Affects common web application components.
Confirm relevance and assess exposure.

Attack Path

How an attacker could exploit the issue

An attacker can leverage this vulnerability by uploading a specially crafted file through a web application that uses a vulnerable version of the class.upload.php library. This could occur in systems like Joomla! with the K2 extension, where the library is integrated for handling file uploads. By exploiting the library's oversight in filtering dangerous file extensions, an attacker could potentially gain unauthorized access and execute arbitrary code.

Unauthenticated remote access required.
Uploading a malicious file triggers vulnerability.
Allows arbitrary code execution.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an attacker to upload malicious files, potentially leading to the execution of arbitrary code on the server when supported by the advisory. This could impact the integrity and availability of the affected system.

Server-side code execution and system compromise.
Uploading specially crafted files through vulnerable components.
Complete loss of system control and data corruption.

Operational Fix

Recommended remediation, mitigation, and detection steps

Security teams and application owners should prioritize identifying all instances of the affected upload library. Confirming the reachability and business criticality of these instances will determine the remediation priority and inform discussions with vendor management if the library is part of a third-party solution. The first practical step is to locate where the vulnerable code resides, assess its exposure, and then plan for mitigation based on the identified risk.

Identify affected systems and owners.
Verify public exposure and business criticality.
Plan coordinated remediation efforts.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is verot.net class.upload.php?

It is a PHP library designed to manage file uploads within web applications. Developers use it to simplify tasks like moving, renaming, and validating files submitted by users. It is frequently integrated into larger software, such as the K2 extension for Joomla!, to handle the mechanics of processing user-provided attachments or media.

What does CVE-2019-19634 mean by arbitrary file upload?

This vulnerability relates to CWE-434, which is the Unrestricted Upload of File with Dangerous Type. In this specific case, the library fails to recognize '.pht' as a dangerous file extension. Because the code does not block this extension, an attacker could upload a file that the web server might mistakenly execute as a script, potentially giving them the ability to run unauthorized commands.

How is this vulnerability triggered?

The flaw is triggered when a user uploads a file with a restricted extension, like '.pht', through a form powered by the vulnerable library code. It is important to note that uploading standard, harmless file types—such as plain text documents or common image formats not targeted by the bypass—does not inherently trigger this specific vulnerability.

Is my system at risk?

Halo Surface Signal indicates that because this library is typically embedded in public-facing web forms, it is frequently found in internet-accessible environments. If your application uses an affected version of the K2 extension or the library directly and exposes file upload features to the public, the risk is higher. You should assess whether these components are reachable from the internet.

What steps should I take if I use this software?

Start by identifying all instances of the affected library within your web environment. Once located, verify which applications rely on these versions and assess their public exposure. Coordinate with your team to review the implementation and plan for updates or security patches provided by the software maintainers or third-party vendors.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.