CVE-2025-0520: ShowDoc RCE via File Upload Flaw Under Active Attack

A critical security flaw impacting ShowDoc, a widely utilized document management and collaboration platform, is currently being exploited in the wild. According to The Hacker News, this vulnerability allows unauthenticated attackers to achieve RCE by bypassing file upload restrictions. The CVE identified as CVE-2025-0520 (also tracked as CNVD-2020-26585) has been assigned a CVSS score of 9.4, reflecting its high severity and ease of exploitation.

Technical Analysis of CVE-2025-0520

The core of the issue lies in the application’s handling of image uploads within its API endpoints. ShowDoc fails to adequately validate the extensions and MIME types of files uploaded to the server. Specifically, the vulnerability resides in the server/index.php?s=/home/page/uploadImg path. While the application is designed to accept only image formats, insufficient server-side checks allow an attacker to upload a PHP script disguised with a double extension or a modified header.

Once the file is successfully uploaded to the Public/Uploads directory, the attacker can navigate directly to the file’s URL. Since the web server environment is typically configured to execute PHP files within this directory, the attacker gains the ability to run arbitrary code under the context of the web user. This sequence of events allows for a complete system compromise, enabling Lateral Movement or data exfiltration from the documentation database.

How to Detect CVE-2025-0520 Exploit Activity

Security teams and SOC analysts should immediately audit their web server logs for suspicious POST requests directed at the ShowDoc upload endpoints. Identifying unusual file names in the upload directory, such as those containing .php, .php5, or .phtml extensions, is a primary IoC. Using an EDR solution to monitor for the spawning of shells (like cmd.exe or /bin/sh) from the web server process is another effective method for detection.

Threat Landscape and Impact

ShowDoc is particularly popular in China for internal technical documentation and API management. Because these platforms often store sensitive intellectual property, network configurations, and credentials, they are high-value targets for an APT or opportunistic ransomware groups. A successful breach of a documentation server provides attackers with a roadmap of the internal network, significantly lowering the barrier for subsequent attacks.

The MITRE ATT&CK framework classifies this technique as Exploit Public-Facing Application (T1190). The transition from a simple file upload to full system access highlights the danger of placing documentation platforms on the public internet without proper Zero Trust controls or multi-factor authentication.

Mitigate ShowDoc File Upload Vulnerability and Prevent RCE

To secure affected environments, organizations must prioritize the following remediation steps:

• Apply Security Updates: Ensure you have applied the ShowDoc version 2.8.6 RCE patch or the most recent stable release available on the official repository.
• Web Server Hardening: Configure the web server (Nginx/Apache) to disable the execution of scripts within the Public/Uploads directory. This acts as a fail-safe even if the application logic is bypassed.
• Egress Filtering: Restrict the server’s ability to initiate outbound connections to prevent the download of second-stage malware or the establishment of a C2 channel.
• Input Validation: Implement stricter server-side validation that checks file signatures (magic bytes) rather than relying solely on file extensions.