ShowDoc RCE Vulnerability CVE-2025-0520 Under Active Exploitation

Executive Summary

A critical remote code execution (RCE) vulnerability in the ShowDoc document collaboration platform, tracked as CVE-2025-0520, is being actively exploited in the wild. The flaw, an unrestricted file upload issue with a CVSS score of 9.4, allows unauthenticated attackers to upload malicious PHP files and gain full control of affected servers. ShowDoc is widely used in China, putting a significant number of internet-facing systems at immediate risk if not patched.

Technical Analysis

The vulnerability, also known as CNVD-2020-26585, resides in ShowDoc's file upload functionality. According to The Hacker News, the flaw stems from improper validation of user-supplied files, specifically within the /index.php?s=/home/page/uploadImg endpoint. This allows an attacker to bypass intended restrictions and upload arbitrary files, including webshells, to the server.

The technical root cause is an insufficient filtering mechanism that fails to verify the file extension or content of uploaded items. Attackers can craft HTTP POST requests containing a malicious PHP file, which the server accepts and stores in a web-accessible directory. Once uploaded, the attacker can directly execute the file by navigating to its location, resulting in remote code execution with the privileges of the web server process. This provides a direct pathway to server compromise, data theft, and further network penetration.

Tactics, Techniques & Procedures

Based on the nature of CVE-2025-0520, the observed exploitation likely follows a consistent pattern. Attackers are scanning for exposed ShowDoc instances, particularly versions prior to the fix. The primary Tactic is Initial Access (TA0001). The key Techniques include:

• T1190: Exploit Public-Facing Application: Targeting the vulnerable /uploadImg endpoint.
• T1505.003: Server Software Component – Web Shell: Uploading a PHP file to establish a persistent backdoor on the compromised server.

The exploitation is straightforward and does not require authentication, making it suitable for automated, large-scale attack campaigns.

Threat Actor Context

The source material does not attribute this exploitation campaign to a specific named threat actor or group. The widespread availability of the vulnerability details and proof-of-concept exploitation code makes it accessible to a broad range of malicious actors, from opportunistic script-kiddies to more advanced groups conducting automated scans for vulnerable infrastructure. The primary motivation appears to be initial server compromise, which can serve as a foothold for subsequent activities like data exfiltration, ransomware deployment, or launching attacks on internal networks.

Mitigations & Recommendations

The most critical action is immediate patching. Administrators must upgrade ShowDoc to a version that addresses CVE-2025-0520. If immediate patching is not possible, the following compensatory controls should be implemented urgently:

1. Network Segmentation: Restrict network access to ShowDoc administration interfaces and instances, ensuring they are not directly exposed to the internet unless absolutely necessary.
2. Web Application Firewall (WAF): Deploy a WAF with rules configured to block HTTP POST requests attempting to upload files with .php extensions or other executable content to the vulnerable endpoint.
3. File Integrity Monitoring: Implement monitoring on web directories for unauthorized file creation, particularly files with executable extensions like .php, .jsp, or .asp in upload directories.
4. Incident Response Review: Organizations running ShowDoc should review server logs for suspicious POST requests to /index.php?s=/home/page/uploadImg and conduct forensic analysis on any uploaded files in web-accessible directories.