CVE-2024-28335: Lektor Path Traversal Vulnerability

CVE-2024-28335 Overview

CVE-2024-28335 is a path traversal vulnerability in Lektor, an open-source static content management system (CMS), affecting versions prior to 3.3.11. The vulnerability stems from improper sanitization of database path traversal sequences, enabling attackers to upload malicious files to the templates directory and achieve remote code execution through shell command execution.

Critical Impact

This vulnerability allows attackers to execute arbitrary shell commands on systems running the Lektor development server by exploiting path traversal in conjunction with cross-origin requests from malicious websites targeting localhost port 5000.

Affected Products

• Lektor Static CMS versions prior to 3.3.11
• Systems running lektor server command on localhost port 5000
• Development environments where users browse untrusted websites while running the Lektor server

Discovery Timeline

• 2024-03-27 - CVE-2024-28335 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-28335

Vulnerability Analysis

This vulnerability exists due to insufficient input validation when handling database path operations within the Lektor CMS. The application fails to properly sanitize path traversal sequences (such as ../), allowing attackers to escape intended directory boundaries and write files to arbitrary locations on the filesystem, including the templates directory.

The attack scenario requires a specific condition where the victim is running the lektor server development command while simultaneously browsing an attacker-controlled website. The malicious website leverages JavaScript to send cross-origin requests to localhost:5000, exploiting the fact that the development server binds to the local interface without proper origin validation.

When a malicious file is successfully placed in the templates directory through path traversal, the Lektor templating engine processes it, leading to arbitrary shell command execution in the context of the user running the server.

Root Cause

The root cause is classified as CWE-22 (Improper Limitation of a Pathname to a Restricted Directory, commonly known as Path Traversal). The Lektor CMS does not adequately validate or sanitize user-supplied path components before using them in filesystem operations. This allows an attacker to construct paths containing directory traversal sequences that escape the intended directory structure.

Attack Vector

The attack leverages a network-based attack vector requiring no authentication or user interaction beyond running the development server while browsing untrusted websites. The exploitation chain works as follows:

1. An attacker hosts a malicious website containing JavaScript code designed to send HTTP requests to localhost:5000
2. The victim, who is running lektor server on their local machine, visits the malicious website
3. The JavaScript sends crafted requests to the local Lektor server containing path traversal sequences
4. Due to insufficient path sanitization, a malicious file is written to the templates directory
5. When the template is processed, arbitrary shell commands embedded in the file are executed

The vulnerability allows attackers to bypass intended directory restrictions and achieve arbitrary file upload, ultimately resulting in remote code execution. Detailed technical information about the exploitation mechanism can be found in the Packet Storm Security Advisory and the CXSecurity Issue Report.

Detection Methods for CVE-2024-28335

Indicators of Compromise

• Unexpected files appearing in the Lektor templates directory
• Unusual HTTP requests to localhost:5000 originating from web browser processes
• Presence of files with path traversal sequences (../) in access logs
• Unexplained shell processes spawned as children of the Lektor server process
• Modified or newly created files in sensitive directories during Lektor server operation

Detection Strategies

• Monitor filesystem activity in Lektor installation directories for unauthorized file creation or modification
• Implement network monitoring to detect unusual localhost traffic patterns to port 5000
• Review web server access logs for requests containing path traversal sequences or encoded variants
• Deploy endpoint detection and response (EDR) solutions to identify suspicious process chains originating from Lektor processes

Monitoring Recommendations

• Enable verbose logging on Lektor development servers to capture all incoming requests
• Implement file integrity monitoring on the templates directory and related Lektor directories
• Use browser extensions or security tools that restrict localhost access from external websites
• Monitor for cross-origin requests targeting local development servers from untrusted origins

How to Mitigate CVE-2024-28335

Immediate Actions Required

• Upgrade Lektor to version 3.3.11 or later immediately
• Avoid running lektor server while browsing untrusted websites
• Restrict the Lektor development server from accepting connections by using firewall rules
• Consider using browser configurations that block localhost access from external origins, as documented in Brave's Privacy Update

Patch Information

The vulnerability has been addressed in Lektor version 3.3.11. The fix implements proper path sanitization to prevent directory traversal attacks. Users should upgrade to this version or later to remediate the vulnerability.

The patch details can be reviewed in the GitHub Pull Request, and the patched version is available at the Lektor v3.3.11 Release.

Workarounds

• Bind the Lektor server to a different port and use firewall rules to restrict access
• Run the Lektor development server in an isolated environment or container
• Use a browser profile without JavaScript enabled when running local development servers
• Implement network-level filtering to block cross-origin requests to localhost from external websites

# Restrict access to Lektor development server using iptables
# Block external access to port 5000
iptables -A INPUT -p tcp --dport 5000 -s 127.0.0.1 -j ACCEPT
iptables -A INPUT -p tcp --dport 5000 -j DROP

# Alternative: Run Lektor in a container with network isolation
docker run --network=none -v $(pwd):/site lektor/lektor server