CVE-2025-27787: Applio Voice Conversion Tool DoS Vulnerability

CVE-2025-27787 Overview

CVE-2025-27787 is a path traversal and denial of service vulnerability in Applio, an open-source voice conversion tool. The vulnerability exists in the restart.py module where the model_name parameter from train.py is used to construct a file path without proper sanitization. An attacker can exploit this flaw to read arbitrary config.json files via path traversal and subsequently kill arbitrary processes on the system, leading to denial of service.

Critical Impact

Remote attackers can cause denial of service by killing arbitrary processes on the server, including the Applio application itself and other critical system processes, through a combination of arbitrary file write and path traversal attacks.

Affected Products

• Applio versions 3.2.8-bugfix and prior
• Applio voice conversion tool (all versions prior to patch)
• Systems running Applio with network-accessible endpoints

Discovery Timeline

• 2025-03-19 - CVE-2025-27787 published to NVD
• 2025-08-01 - Last updated in NVD database

Technical Details for CVE-2025-27787

Vulnerability Analysis

This vulnerability combines two dangerous attack patterns: path traversal (CWE-22) and arbitrary process termination. The model_name parameter in train.py accepts user input and passes it to the stop_train function in restart.py. This function constructs a path to a config.json file using the unsanitized input, reads the process_pids array from that JSON file, and then terminates all processes with those IDs.

The attack chain requires exploiting an arbitrary file write vulnerability first to plant a malicious config.json file containing target process IDs. Once the file is in place, an attacker triggers the vulnerable endpoint with a crafted model_name to read the malicious configuration and kill the specified processes. Since process IDs are typically unpredictable, an attacker can include hundreds of process IDs in their payload to maximize disruption, potentially killing the Applio server process itself along with other critical system services.

Root Cause

The root cause is improper input validation in the path construction logic within restart.py. User-supplied input (model_name) is directly concatenated into a file path without sanitization, enabling directory traversal sequences like ../../ to escape the intended directory structure. Additionally, the application blindly trusts the contents of config.json files and executes process kill operations based on the process_pids values without any validation or authorization checks.

Attack Vector

The vulnerability is exploitable over the network without authentication. An attacker first leverages an arbitrary file write primitive to place a malicious config.json file in a predictable location such as logs/foobar. This file contains a JSON array of process IDs under the process_pids key. The attacker then sends a request to the training endpoint with a crafted model_name value that traverses to the planted file. When processed, the application reads the malicious configuration and terminates all listed processes.

The path traversal component allows attackers to supply values like ../../ in the model_name parameter to access config.json files from directories outside the intended scope, potentially two or more levels up the directory hierarchy from the application root.

Detection Methods for CVE-2025-27787

Indicators of Compromise

• Unexpected config.json files appearing in the logs/ directory or other writable locations
• HTTP requests containing path traversal sequences (../, ..%2f) in the model_name parameter
• Unusual process termination events or sudden service outages
• Log entries showing access to training endpoints with suspicious model name values

Detection Strategies

• Monitor web application logs for requests containing directory traversal patterns in input parameters
• Implement file integrity monitoring on the Applio installation directory to detect unauthorized file creation
• Set up process monitoring alerts for unexpected termination of the Applio service and related processes
• Deploy web application firewall rules to block requests containing path traversal sequences

Monitoring Recommendations

• Enable verbose logging for all training-related endpoints in Applio
• Configure system auditing to track file creation events in the application directory
• Monitor for abnormal patterns in process termination system calls
• Implement anomaly detection for unusual file access patterns in the logs directory

How to Mitigate CVE-2025-27787

Immediate Actions Required

• Restrict network access to Applio instances to trusted users and networks only
• Implement input validation to reject model_name values containing path traversal sequences
• Consider running Applio in a containerized environment to limit process termination impact
• Review and restrict file system permissions for the Applio user account

Patch Information

As of the publication date, no official patch is available from the vendor. Users should monitor the GitHub Security Advisory for updates on remediation. The vulnerability was identified in the following code locations:

• restart.py line 9
• train.py line 306

Workarounds

• Deploy Applio behind a reverse proxy with strict input validation rules that reject path traversal attempts
• Run Applio with minimal privileges and in an isolated environment (container, VM, or sandbox)
• Implement network segmentation to limit access to the Applio service to authorized users only
• Remove or restrict write permissions to directories where malicious config.json files could be planted

# Example: Restrict Applio network access using iptables
# Allow only specific trusted IPs to access Applio
iptables -A INPUT -p tcp --dport 7865 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 7865 -j DROP

# Example: Run Applio with restricted permissions
# Create dedicated user with minimal privileges
useradd -r -s /bin/false applio_user
chown -R applio_user:applio_user /opt/applio
chmod -R 750 /opt/applio