CVE-2019-25586: Deluge-torrent Deluge DoS Vulnerability

CVE-2019-25586 Overview

CVE-2019-25586 is a denial of service vulnerability affecting Deluge version 1.3.15, a popular open-source BitTorrent client. The vulnerability allows local attackers to crash the application by supplying an excessively long string in the URL field. Specifically, attackers can paste a buffer of 5000 characters into the 'From URL' field during torrent addition to trigger an application crash, resulting in service disruption for users.

Critical Impact

Local attackers can cause application crashes and denial of service by exploiting improper input validation in the URL field, disrupting torrent download operations.

Affected Products

• deluge-torrent deluge version 1.3.15

Discovery Timeline

• 2026-03-22 - CVE-2019-25586 published to NVD
• 2026-03-24 - Last updated in NVD database

Technical Details for CVE-2019-25586

Vulnerability Analysis

This vulnerability is classified under CWE-466 (Return of Pointer Value Outside of Expected Range), indicating that the application fails to properly handle input boundaries in the URL parsing functionality. The vulnerability exists in the torrent addition workflow where users can specify a URL to download torrent files from.

The Deluge application does not implement adequate input length validation for the 'From URL' field. When a user or local attacker inputs an extremely long string (approximately 5000 characters), the application fails to handle this input gracefully, resulting in an application crash. This represents a classic input validation vulnerability that impacts application availability.

The attack requires local access to the system where Deluge is installed, limiting its scope compared to remote vulnerabilities. However, in shared computing environments or scenarios where attackers have limited local access, this vulnerability could be leveraged to disrupt services for legitimate users.

Root Cause

The root cause of this vulnerability lies in insufficient input validation within Deluge's URL handling mechanism. The application lacks proper boundary checks on user-supplied input in the 'From URL' field, allowing excessively long strings to be processed without sanitization or length restrictions. This oversight results in memory handling issues that crash the application when attempting to process malformed input.

Attack Vector

The attack vector is local, requiring the attacker to have access to the Deluge application interface. The attacker must navigate to the torrent addition dialog and paste an excessively long string (5000+ characters) into the 'From URL' field. Upon submission or processing of this input, the application crashes, denying service to the user.

The attack is straightforward to execute, requiring no authentication bypass or privilege escalation. The exploitation process involves:

1. Opening the Deluge application
2. Navigating to the "Add Torrent" functionality
3. Selecting the "From URL" option
4. Pasting a string exceeding 5000 characters
5. Triggering the input processing, which causes the crash

For technical details and proof-of-concept information, see the Exploit-DB #46883 entry and the VulnCheck Deluge DoS Advisory.

Detection Methods for CVE-2019-25586

Indicators of Compromise

• Unexpected Deluge application crashes or termination events
• Windows Event Logs or system logs showing Deluge process failures with memory-related error codes
• User reports of application instability when adding torrents via URL
• Crash dump files indicating buffer handling failures in Deluge processes

Detection Strategies

• Monitor system logs for recurring Deluge application crashes
• Implement application-level monitoring to detect abnormal process terminations
• Deploy endpoint detection solutions to identify patterns of repeated application failures
• Review crash reports for evidence of input-triggered application failures

Monitoring Recommendations

• Enable application crash logging and configure alerts for Deluge process termination
• Use endpoint protection platforms to monitor for denial of service patterns
• Implement user behavior analytics to identify unusual application usage patterns
• Consider deploying SentinelOne Singularity to detect and respond to application-level anomalies

How to Mitigate CVE-2019-25586

Immediate Actions Required

• Upgrade Deluge to a version newer than 1.3.15 that includes proper input validation
• Restrict local access to systems running vulnerable Deluge installations
• Consider using alternative torrent clients until the vulnerable version can be upgraded
• Implement application allowlisting to control which users can access the Deluge application

Patch Information

Users should upgrade to a newer version of Deluge that addresses this input validation vulnerability. Visit the Deluge Torrent Development Site for the latest releases and security updates. The affected Windows installer can be found at Deluge Torrent Windows Installer for reference when verifying currently installed versions.

Workarounds

• Restrict physical and remote access to systems running vulnerable Deluge versions
• Educate users about the vulnerability and advise against pasting untrusted content into URL fields
• Consider implementing network-based torrent file delivery instead of URL-based addition
• Deploy application sandboxing to limit the impact of potential crashes

# Verify current Deluge version and consider upgrade
deluge --version

# On Debian/Ubuntu systems, upgrade to latest available version
sudo apt-get update && sudo apt-get upgrade deluge

# On Windows, download latest installer from official site
# https://dev.deluge-torrent.org/