CVE-2026-23835: LobeHub File Upload DoS Vulnerability

CVE-2026-23835 Overview

CVE-2026-23835 is an improper input validation vulnerability affecting LobeHub, an open source human-and-AI-agent network platform. The vulnerability exists in the file upload feature within the Knowledge Base > File Upload functionality, which fails to validate the integrity of upload request parameters. This allows authenticated users to intercept and modify request parameters, enabling arbitrary file creation in unintended paths and manipulation of file size reporting for quota bypass.

Critical Impact

Attackers can bypass monthly upload quotas, create arbitrary files in unintended paths, and cause resource exhaustion leading to denial of service for legitimate users.

Affected Products

• LobeHub versions prior to 1.143.3
• LobeChat (lobechat.com) cloud service
• Self-hosted LobeHub deployments with Knowledge Base functionality enabled

Discovery Timeline

• 2026-01-30 - CVE CVE-2026-23835 published to NVD
• 2026-02-04 - Last updated in NVD database

Technical Details for CVE-2026-23835

Vulnerability Analysis

This vulnerability is classified under CWE-73 (External Control of File Name or Path), where the application fails to properly validate user-controlled input that influences file system operations. The core issue stems from the Knowledge Base file upload feature trusting client-provided parameters without server-side validation.

The vulnerability presents two distinct attack surfaces. First, the file path parameter can be manipulated to create files in arbitrary or abnormal locations within the file system. Second, the size parameter used for quota calculations can be falsified, allowing attackers to report inaccurate file sizes to the billing and quota enforcement systems.

Because lobechat.com relies on the size parameter from the client request to calculate file usage and enforce storage quotas, an attacker can upload a 1 GB file while reporting it as 10 MB, or conversely, falsely declare a 10 MB file as 1 GB. This creates a significant discrepancy between actual resource consumption and billing calculations.

Root Cause

The root cause is improper input validation in the file upload request handler. The server trusts client-provided values for critical parameters including file paths and file sizes without performing server-side integrity verification. This violates the security principle of never trusting client-side input for security-critical decisions such as quota enforcement and file storage location.

Attack Vector

The attack can be executed remotely over the network by any authenticated user with access to the Knowledge Base file upload functionality. An attacker intercepts the file upload HTTP request using a proxy tool, modifies the path parameter to specify an arbitrary file location, and adjusts the size parameter to misrepresent the actual file size.

This manipulation enables several attack scenarios: bypassing monthly upload quotas to continuously upload files beyond storage limits, causing billing discrepancies that result in financial impact to service operators, exhausting storage resources to degrade service availability for legitimate users, and affecting other users sharing the same subscription plan in a multi-tenant environment.

The vulnerability description notes that excessive uploads can also distort monitoring metrics and overload downstream systems such as backup processes, malware scanning, and media processing pipelines.

Detection Methods for CVE-2026-23835

Indicators of Compromise

• Unusual discrepancies between reported file sizes in upload logs and actual file sizes on disk
• Files appearing in unexpected directories outside of standard upload paths
• Sudden spikes in storage consumption without corresponding quota deductions
• Upload requests with manipulated size parameters that don't match actual content length

Detection Strategies

• Implement server-side file size verification by comparing reported size against actual uploaded content length
• Monitor for path traversal patterns or unexpected directory references in upload requests
• Audit file creation events for files appearing outside designated upload directories
• Cross-reference billing records with actual storage utilization to identify discrepancies

Monitoring Recommendations

• Enable detailed logging for all file upload operations including request parameters and actual file metadata
• Set up alerts for storage consumption anomalies that exceed reported quota usage
• Monitor for rapid successive uploads from single users that may indicate quota bypass attempts
• Track downstream system load on backup, scanning, and processing pipelines for unusual activity

How to Mitigate CVE-2026-23835

Immediate Actions Required

• Upgrade LobeHub to version 1.143.3 or later immediately
• Audit existing uploaded files for any stored in unexpected locations
• Review storage consumption against billing records to identify potential exploitation
• Temporarily restrict file upload access if patching cannot be performed immediately

Patch Information

The vulnerability has been addressed in LobeHub version 1.143.3. Organizations running affected versions should upgrade immediately. For detailed patch information and security advisory, refer to the GitHub Security Advisory GHSA-wrrr-8jcv-wjf5.

Workarounds

• Implement a reverse proxy or WAF rule to validate file upload request parameters before reaching the application
• Restrict access to the Knowledge Base file upload feature to trusted users only
• Deploy server-side file size verification at the infrastructure level to override client-reported values
• Monitor and enforce hard storage limits at the filesystem or cloud storage provider level

# Example: Restrict upload directory permissions and implement quota at filesystem level
# Set strict permissions on upload directory
chmod 750 /var/lobehub/uploads
chown lobehub:lobehub /var/lobehub/uploads

# Implement filesystem quota (Linux)
setquota -u lobehub 5G 6G 0 0 /var/lobehub