External risk intelligence

DedeCMS PHP Code Injection leading to Command Execution

CVE advisorySeverity: CRITICAL (CVSS 9.3)

CVE-2021-48016

The vulnerability exists in a Content Management System (CMS), which is a type of application typically deployed as a public-facing web service to manage website content. As the exploit is reachable via standard HTTP requests to a specific PHP script within the application, it commonly resides on internet-exposed web servers.

Code Injection

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 advisory details a critical vulnerability in DedeCMS, a content management system. The flaw allows unauthenticated attackers to execute arbitrary code on affected systems by manipulating HTTP headers. This could potentially lead to a compromise of the underlying server.

Allows unauthorized code execution.
Impacts systems using DedeCMS.
Confirm relevance and potential exposure.

Attack Path

How an attacker could exploit the issue

An unauthenticated attacker can exploit this vulnerability by sending a specially crafted HTTP Referer header to the `flink.php` script. This crafted header will be processed by the `ShowMsg()` function, leading to arbitrary PHP code execution on the server. This can allow an attacker to run system commands.

No authentication required.
Craft HTTP Referer header.
Execute arbitrary code and commands.

Live Threat

Current exploitation, exposure, and threat context

A PHP code injection vulnerability in DedeCMS could allow unauthenticated attackers to execute arbitrary PHP code and system commands. This could occur when an attacker sends a crafted HTTP Referer header to the `flink.php` script.

System commands could be executed.
Arbitrary code execution is possible.
Unauthenticated remote command execution.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability affects DedeCMS, a content management system often deployed on public-facing web servers. Responsibility for addressing this issue likely falls to application owners, web administrators, or platform teams managing the DedeCMS instances. The immediate first step should be to identify all deployed instances, assess their exposure and business criticality, and then prioritize remediation based on risk, coordinating with vendor management if applicable.

Application owners should own this issue.
Verify public exposure and business criticality.
Plan risk-based remediation and vendor coordination.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

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Frequently asked questions

What is DedeCMS?

DedeCMS is a popular PHP-based Content Management System (CMS) often used to build and manage dynamic websites. It provides frameworks for users to publish content, handle media, and manage site architecture. Like many web platforms, it relies on server-side scripts to process user interactions and templates, which is where this specific vulnerability resides.

What does CWE-94 mean in the context of CVE-2021-48016?

CWE-94 refers to Improper Control of Generation of Code, commonly known as Code Injection. In this CVE, the vulnerability allows an attacker to inject unauthorized PHP instructions into the system. Because the application improperly handles data provided in an HTTP header, it inadvertently treats that input as executable code, granting the attacker control over the server's command execution.

How does an attacker trigger this DedeCMS vulnerability?

An attacker triggers this flaw by sending a specifically crafted HTTP Referer header to the flink.php script. The vulnerability requires no authentication, meaning anyone can send this request. It is important to note that the issue specifically relates to how the ShowMsg() function processes this header; simply visiting the site normally or using other, unaffected scripts will not trigger the bug.

Is my instance at risk according to Halo Surface Signal?

Because DedeCMS is a Content Management System typically deployed as a public-facing web service, Halo Surface Signal classifies this as highly likely to be internet-exposed. Since the exploit is reachable via standard HTTP requests to a specific script, any instance accessible from the internet is at elevated risk of being targeted by unauthorized remote commands.

What should I do first to address CVE-2021-48016?

Your first step is to perform an inventory to identify all instances of DedeCMS running in your environment. Once identified, evaluate the criticality and internet exposure of each server. Since this vulnerability allows for unauthenticated command execution, prioritize patching or updating your CMS instances and coordinate with your web administrators to restrict access to the affected script while remediation plans are finalized.

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.