External risk intelligence

Langchain-Chatchat Path Traversal Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.1)

CVE-2026-51883

Langchain-Chatchat is a web-based application designed for document interaction and knowledge base management. These interfaces are commonly deployed as web applications or services accessible via a network, often intended for user interaction, making the document upload and knowledge base features common targets for web-based exposure.

Path Traversal

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability exists in Langchain-Chatchat's knowledge base and document upload features, allowing an attacker to write files to arbitrary locations on the server by manipulating file names. This could potentially lead to unauthorized data access or modification. The main concern is confirming relevance and exposure.

Path traversal allows writing files anywhere.
Affects knowledge base and document upload features.
Confirm if your systems use this specific tool.

Attack Path

How an attacker could exploit the issue

An attacker could target the knowledge base creation and document upload features of this application. By providing specially crafted input, they can manipulate the system to write files to unintended locations on the server, potentially impacting the integrity of the system.

Requires network access.
Involves uploading documents.
Leads to arbitrary file writes.

Live Threat

Current exploitation, exposure, and threat context

A path traversal vulnerability in Langchain-Chatchat could allow an unauthenticated attacker to write arbitrary content to any location on the server's file system that the application has write permissions for, by manipulating the `knowledge_base_name` parameter during knowledge base creation or document upload. This could impact system integrity by overwriting critical files or introducing malicious content.

System files could be overwritten.
Attackers can write files via a web interface.
System integrity may be compromised.

Operational Fix

Recommended remediation, mitigation, and detection steps

The vulnerability in Langchain-Chatchat's knowledge base creation and document upload interfaces requires immediate attention from teams responsible for application security and infrastructure. The first critical step is to identify all instances of the affected technology, assess their exposure and business criticality, and then pinpoint the accountable owner for remediation planning.

Application owners should take ownership.
Verify external access and critical systems first.
Plan remediation based on exposure and criticality.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is Langchain-Chatchat?

Langchain-Chatchat is an open-source application framework designed to create local, private LLM-based knowledge bases. It allows users to interact with their own document collections through a web-based interface. The tool manages document uploading and indexing, functioning as a service that bridges large language models with your personal data.

What does CVE-2026-51883 mean in plain English?

This vulnerability is classified as CWE-22, or Path Traversal. It means the software fails to properly sanitize input when handling file paths. In this specific case, an attacker can manipulate the knowledge base name to bypass directory restrictions, allowing them to write files into unintended areas of the server's file system rather than just the designated storage folder.

How does an attacker trigger this vulnerability?

An attacker triggers this by injecting malicious path sequences, such as '..\', into the 'knowledge_base_name' parameter during the document upload or knowledge base creation process. Simply navigating the application's standard user interface for legitimate uploads does not trigger the bug; it requires specifically crafted input designed to escape the intended directory boundaries.

How do I know if my Langchain-Chatchat instance is at risk?

According to Halo Surface Signal, this software is typically deployed as a network-accessible web service for user interaction. You should determine if your instance is internet-facing or reachable by untrusted users. Since the vulnerability allows file writes via the web interface, any deployment exposed to a network is at higher risk than an instance restricted to a local, isolated environment.

What should I do if I use Langchain-Chatchat?

First, conduct an inventory to identify all active instances of the affected versions (0.3.0 and 0.3.1) within your infrastructure. Once identified, prioritize instances by their network accessibility and business importance. Assign ownership to the relevant technical teams so they can prepare for remediation, such as restricting access or applying authorized updates as they become available.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.