CVE-2021-47835: Freeter 1.2.1 XSS Vulnerability

CVE-2021-47835 Overview

CVE-2021-47835 is a persistent cross-site scripting (XSS) vulnerability affecting Freeter version 1.2.1, a productivity application designed for organizing work files and tools. The vulnerability allows attackers to store malicious payloads within custom widget titles and files. When victims interact with these crafted elements within the application, embedded scripts execute in the context of the victim's session, potentially enabling remote code execution.

Critical Impact

Attackers can achieve persistent code execution by embedding malicious scripts in widget titles and files, which execute whenever victims interact with the compromised application elements.

Affected Products

• Freeter 1.2.1
• Freeter applications with custom widget functionality

Discovery Timeline

• January 16, 2026 - CVE-2021-47835 published to NVD
• January 16, 2026 - Last updated in NVD database

Technical Details for CVE-2021-47835

Vulnerability Analysis

This persistent cross-site scripting vulnerability (CWE-79) exists in how Freeter handles user-supplied input within custom widget titles and file content. The application fails to properly sanitize or encode user input before rendering it in the application's interface, allowing attackers to inject and persist malicious JavaScript code.

The vulnerability requires network access and user interaction to exploit. An attacker must craft malicious content and convince the victim to interact with it within the Freeter application. Once triggered, the injected scripts execute with the same privileges as the application, potentially allowing attackers to steal sensitive data, modify application behavior, or pivot to more severe attacks such as remote code execution given Freeter's desktop application context.

Root Cause

The root cause is improper input validation and insufficient output encoding in Freeter's widget rendering functionality. When users create or modify widget titles, the application stores the raw input without sanitization. Upon rendering, this unsanitized content is interpreted as executable code rather than treated as data, enabling script injection attacks.

Attack Vector

The attack leverages the network-accessible nature of shared Freeter projects or imported files. An attacker crafts a malicious file containing embedded JavaScript payloads or creates a widget with a script-injected title. When a victim opens or interacts with the malicious content, the scripts execute within the Electron-based application context.

The attack chain typically involves:

1. Attacker creates a malicious Freeter project or widget configuration containing XSS payloads
2. Victim imports or opens the attacker-controlled content
3. Malicious scripts execute when the victim views or interacts with the compromised widgets
4. Attacker achieves code execution within the application's context, potentially escalating to system-level access

Technical details and a proof-of-concept demonstration are available in the Exploit-DB #49833 entry.

Detection Methods for CVE-2021-47835

Indicators of Compromise

• Presence of <script> tags or JavaScript event handlers (onerror, onload, onclick) within Freeter widget titles or configuration files
• Unusual network connections initiated by the Freeter application process
• Unexpected child processes spawned by Freeter during normal operation
• Modified or suspicious Freeter project files with encoded or obfuscated content

Detection Strategies

• Monitor Freeter configuration directories for files containing suspicious HTML/JavaScript patterns
• Implement file integrity monitoring on Freeter project storage locations
• Deploy endpoint detection rules to identify script injection patterns in application data files
• Review imported Freeter projects for embedded executable content before opening

Monitoring Recommendations

• Enable logging for Freeter application activity and monitor for anomalous behavior
• Configure web proxy logs to capture unexpected outbound connections from Freeter processes
• Implement behavioral monitoring for Electron-based applications attempting to execute system commands
• Alert on creation or modification of Freeter project files from untrusted sources

How to Mitigate CVE-2021-47835

Immediate Actions Required

• Avoid importing Freeter projects or files from untrusted sources
• Review existing Freeter widget configurations for suspicious content
• Consider disabling or restricting custom widget functionality until a patch is applied
• Isolate Freeter application usage from sensitive network resources

Patch Information

Users should check the official Freeter website for updated versions that address this vulnerability. The VulnCheck Advisory on Freeter provides additional guidance on remediation steps.

Workarounds

• Only use Freeter projects created internally or from verified trusted sources
• Implement application sandboxing to limit the impact of potential exploitation
• Use content security policies at the organizational level to restrict script execution
• Consider alternative productivity tools until the vendor releases a security update

# Content inspection for suspicious patterns in Freeter files
# Review widget configurations before importing
grep -r -E "<script|onerror=|onload=|javascript:" ~/.config/Freeter/