A critical ShowDoc RCE vulnerability (CNVD-2020-26585) is currently being actively exploited in the wild, putting organizations at serious risk of remote compromise.
ShowDoc is widely used by IT and DevOps teams for internal documentation, API specs, and collaboration workflows. However, this convenience comes with high risk when exposed or misconfigured.
Security researchers confirm that attackers can exploit this flaw to achieve unauthenticated remote code execution (RCE) by uploading malicious files to vulnerable servers.
Because ShowDoc often contains sensitive internal architecture details, API endpoints, and system documentation, successful exploitation can provide attackers with a direct entry point into enterprise networks.
What Is the ShowDoc RCE Vulnerability (CNVD-2020-26585)?
The ShowDoc RCE vulnerability is a critical security flaw caused by unrestricted file upload handling in ShowDoc versions prior to 2.8.7.
Key issue:
The application fails to properly validate uploaded file types through its image upload API.
This allows attackers to:
- Upload executable PHP files disguised as images
- Bypass extension-based validation
- Execute arbitrary code on the server
How the ShowDoc RCE Exploit Works
The vulnerability is particularly dangerous because it requires no authentication and only a single crafted HTTP request.
Attack flow overview
1. Target vulnerable endpoint
Attackers send a request to:
/index.php?s=/home/page/uploadImg
2. Bypass file validation
They manipulate upload metadata such as:
- Filename tricks (e.g.,
test.<>php) - Content-Disposition header injection
This bypasses weak extension filtering logic.
3. Upload malicious payload
Attackers embed:
- PHP web shells
- Remote command execution scripts
- Arbitrary system commands
inside multipart form data.
4. Server stores executable file
The server responds with a URL pointing to the uploaded file.
5. Execute remote code
Visiting the uploaded file URL triggers:
- PHP execution on the server
- Full remote code execution (RCE)
- Web server-level compromise
Why This Vulnerability Is Actively Exploited
Security reports indicate that:
- Exploit code is publicly available
- Automated scanners actively target exposed ShowDoc instances
- Vulnerable servers are being rapidly discovered and attacked
High-risk factors include:
- No authentication required
- Single-request exploitation
- Public exploit scripts available
- Common exposure of internal documentation tools
This combination makes ShowDoc a high-value target for opportunistic attackers and automated botnets.
Impact of ShowDoc RCE Vulnerability
A successful exploit can lead to:
1. Full server compromise
Attackers gain execution rights under web server privileges.
2. Internal network access
ShowDoc often sits inside trusted environments, enabling lateral movement.
3. Data exposure
Potential access to:
- API keys
- Architecture diagrams
- Internal system documentation
4. Persistent backdoors
Attackers can install:
- Web shells
- Reverse shells
- Credential harvesting tools
Risk summary table
| Factor | Impact |
|---|---|
| Authentication required | None |
| Exploit complexity | Low |
| Attack type | Remote Code Execution |
| Exposure risk | High (internal tools) |
Affected Versions
- ShowDoc all versions before 2.8.7
Attack Surface in Real Environments
ShowDoc becomes especially dangerous when:
- Exposed to the public internet
- Used without strict access controls
- Integrated into CI/CD or DevOps pipelines
- Hosting sensitive internal documentation
Mitigation and Security Recommendations
1. Immediate upgrade (critical)
Upgrade ShowDoc to:
- Version 2.8.7 or later
2. Restrict network exposure
- Do not expose ShowDoc publicly
- Restrict access to VPN or internal networks
- Apply IP allowlisting where possible
3. Monitor web server logs
Security teams should inspect:
- POST requests to
/uploadImg - Unexpected file upload patterns
- Requests with unusual filename structures
4. Deploy Web Application Firewall (WAF)
Configure WAF rules to:
- Block PHP or executable file uploads
- Detect malformed multipart requests
- Filter suspicious content-disposition headers
5. Disable unnecessary upload functionality
If possible:
- Restrict or disable image upload endpoints
- Enforce strict file type validation server-side
Expert Security Insights
This vulnerability highlights a classic but still dangerous issue:
File upload mechanisms remain one of the most exploited attack vectors in web applications.
Key lessons:
- Client-side validation is not security
- File extension checks are easily bypassed
- Upload endpoints must treat all input as hostile
Mapped to:
- OWASP Top 10: A03 Injection & A05 Security Misconfiguration
- MITRE ATT&CK: T1190 (Exploit Public-Facing Application)
FAQs
What is the ShowDoc RCE vulnerability?
It is a critical flaw (CNVD-2020-26585) allowing remote code execution via malicious file uploads.
Is authentication required to exploit it?
No. Attackers can exploit it without authentication.
Which versions are affected?
All ShowDoc versions prior to 2.8.7.
How is it exploited?
Through a malicious file upload to the image upload API endpoint.
What is the impact of exploitation?
Full remote code execution and potential internal network compromise.
How can organizations protect themselves?
By upgrading, restricting access, and deploying WAF protections.
Conclusion
The ShowDoc RCE vulnerability (CNVD-2020-26585) is a high-risk security issue that is currently being actively exploited in the wild.
Due to its unauthenticated nature and simple exploit path, it poses a serious threat to organizations using ShowDoc for internal documentation.
Immediate patching, network restriction, and upload hardening are essential to prevent compromise.
