CVE-2025-6776: Openvpn-cms-flask Path Traversal Flaw

CVE-2025-6776 Overview

A critical path traversal vulnerability has been identified in xiaoyunjie openvpn-cms-flask versions up to 1.2.7. This vulnerability affects the Upload function in the file app/plugins/oss/app/controller.py within the File Upload component. An attacker can manipulate the image argument to achieve path traversal, potentially allowing unauthorized file access or modification on the affected system. The attack can be initiated remotely without authentication, making this a significant security concern for organizations using this OpenVPN management platform.

Critical Impact

Remote attackers can exploit this path traversal vulnerability to write files to arbitrary locations on the server, potentially leading to code execution, configuration tampering, or sensitive data exposure.

Affected Products

• xiaoyunjie openvpn-cms-flask versions up to 1.2.7
• Deployments using the vulnerable app/plugins/oss/app/controller.py File Upload component
• Docker deployments using affected container images

Discovery Timeline

• 2025-06-27 - CVE-2025-6776 published to NVD
• 2026-01-30 - Last updated in NVD database

Technical Details for CVE-2025-6776

Vulnerability Analysis

This vulnerability is classified as a Path Traversal (CWE-22) issue in the file upload functionality of openvpn-cms-flask. The Upload function in app/plugins/oss/app/controller.py fails to properly sanitize the image parameter before using it in file system operations. This allows remote attackers to craft malicious requests containing directory traversal sequences (such as ../) to write files outside the intended upload directory.

The vulnerability is network-accessible and requires no authentication or user interaction to exploit. An attacker can leverage this flaw to overwrite critical system files, plant malicious scripts in web-accessible directories, or access sensitive configuration files. The exploit has been publicly disclosed, increasing the risk of active exploitation in the wild.

Root Cause

The root cause of this vulnerability lies in insufficient input validation within the Upload function. The image argument is directly used in file path construction without proper sanitization to remove or neutralize path traversal sequences. This allows attackers to escape the designated upload directory and access or modify files elsewhere on the filesystem. Proper implementation should include strict validation of filenames, removal of special characters, and enforcement of a canonical path within the allowed upload directory.

Attack Vector

The attack vector is network-based, allowing remote exploitation without authentication. An attacker can send a crafted HTTP request to the file upload endpoint with a malicious filename containing path traversal sequences in the image parameter. The server processes this request and writes the uploaded content to an attacker-controlled location on the filesystem.

The security patch in commit e23559b98c8ea2957f09978c29f4e512ba789eb6 addresses this issue along with infrastructure updates:

 
 # python
 RUN set -ex \
+    && yum makecache \
     && yum install -y gcc GeoIP GeoIP-devel net-tools  \
     && pip3 install --no-cache-dir -r requirements.txt  -i https://pypi.tuna.tsinghua.edu.cn/simple \
     && sed -i s/localhost/mysql/g  /opt/openvpn-cms-flask/app/config/secure.py

Source: GitHub Commit

The version bump in the Makefile confirms the release of the patched version:

 all: build push
 
 build:
-	docker build --pull --platform linux/amd64 -t registry.cn-hangzhou.aliyuncs.com/browser/openvpn-cms-flask:v1.2.7 .
+	docker build --pull --platform linux/amd64 -t registry.cn-hangzhou.aliyuncs.com/browser/openvpn-cms-flask:v1.2.8 .
 
 push:
-	docker push registry.cn-hangzhou.aliyuncs.com/browser/openvpn-cms-flask:v1.2.7
+	docker push registry.cn-hangzhou.aliyuncs.com/browser/openvpn-cms-flask:v1.2.8
 
 .PHONY: all build push

Source: GitHub Commit

Detection Methods for CVE-2025-6776

Indicators of Compromise

• HTTP requests to file upload endpoints containing path traversal sequences such as ../, ..%2f, or ..%5c in the image parameter
• Unexpected files appearing in system directories outside the designated upload folder
• Web server logs showing unusual POST requests to /plugins/oss/ endpoints with malformed filenames
• Modified or newly created files with timestamps matching suspicious upload activity

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block path traversal patterns in HTTP request parameters
• Monitor file system integrity on the server, particularly in sensitive directories such as /etc/, /var/www/, and application configuration paths
• Review web server access logs for requests containing encoded traversal sequences targeting upload functionality
• Deploy application-level logging to track all file upload operations and their target paths

Monitoring Recommendations

• Enable verbose logging for the openvpn-cms-flask application to capture all file upload attempts and their destination paths
• Configure file integrity monitoring (FIM) on critical system directories to detect unauthorized modifications
• Set up alerts for HTTP 4xx/5xx responses from the upload endpoint that may indicate exploitation attempts
• Monitor for unusual outbound connections from the server that could indicate post-exploitation activity

How to Mitigate CVE-2025-6776

Immediate Actions Required

• Upgrade openvpn-cms-flask to version 1.2.8 or later immediately
• Review server file systems for any evidence of unauthorized file writes or modifications
• Audit access logs for historical exploitation attempts targeting the file upload endpoint
• Restrict network access to the application to trusted sources while patching is in progress

Patch Information

The vulnerability is addressed in version 1.2.8 of openvpn-cms-flask. The fix is available in commit e23559b98c8ea2957f09978c29f4e512ba789eb6. Organizations should upgrade to the patched version as soon as possible. The official release is available at the GitHub Release v1.2.8. Additional technical details can be found in the GitHub Issue Tracker.

Workarounds

• Implement a reverse proxy or WAF rule to filter requests containing path traversal patterns before they reach the application
• Restrict file upload functionality to authenticated users only with proper authorization checks
• Apply filesystem-level access controls to limit the application's write permissions to only the necessary upload directory
• Consider temporarily disabling the file upload feature if it is not critical for operations until patching can be completed

# Example WAF rule to block path traversal attempts (ModSecurity)
SecRule ARGS "@contains ../" "id:100001,phase:2,deny,status:403,msg:'Path traversal attempt blocked'"
SecRule ARGS "@contains ..%2f" "id:100002,phase:2,deny,status:403,msg:'Encoded path traversal attempt blocked'"