Synapse bot

What is Synapse?

Synapse appears in several contexts across web technology, with three primary implementations. Apache Synapse is an open-source mediation framework developed by The Apache Software Foundation for routing, transformation, and protocol switching in web services. It identifies itself with the user-agent string Mozilla/4.0 (compatible; Synapse). This implementation functions as a lightweight HTTP client that doesn't support JavaScript, cookies, or dynamic content rendering.

In enterprise environments, the WSO2 API Gateway (which uses Apache Synapse) replaces original user agents with Synapse-PT-HttpComponents-NIO. This practice centralizes traffic identification but can obscure client-specific details in logs.

Microsoft's Azure Synapse Analytics represents a different implementation entirely. This cloud-based analytics service employs service principals and agents that facilitate data integration between systems. These components operate with specific user agent strings that identify them as part of the Azure ecosystem.

Why is Synapse crawling my site?

When you see Synapse user agents in your logs, the context matters significantly. Apache Synapse-based bots typically crawl websites to collect structured data, often as part of data integration processes or API interactions. These visits are generally programmatic and focused on specific endpoints rather than general browsing.

The WSO2 implementation might appear when your site is being accessed through an enterprise API gateway, indicating that a business partner or service is interacting with your API endpoints. These requests replace the original client's user agent, making them appear as coming from Synapse directly.

Unfortunately, security researchers have noted that the Apache Synapse user agent has been associated with probing activities and potential attack attempts. Some malicious actors leverage tools built with the Synapse library to mask reconnaissance activities. If you're seeing unusual patterns or suspicious requests from this user agent, particularly against non-API endpoints, this may warrant further investigation.

What is the purpose of Synapse?

The legitimate purpose of Apache Synapse is to facilitate communication between web services and applications. It serves as middleware that enables different systems to exchange data efficiently, transforming messages between formats and protocols as needed. For organizations using WSO2's API Gateway, it centralizes API management and provides a consistent way to handle external requests.

Azure Synapse Analytics focuses on data integration and analytics in the Microsoft cloud ecosystem. Its agents connect various data sources and enable sophisticated analysis workflows.

When used properly, these technologies provide valuable infrastructure for system integration and data processing. However, the same capabilities that make them useful for legitimate purposes can be repurposed for unauthorized data collection or security probing when deployed by third parties without permission.

How do I block Synapse?

For Apache Synapse-based crawlers, you can use robots.txt directives to request that legitimate bots respect your crawling preferences:

User-agent: Synapse
Disallow: /

For the WSO2 API Gateway variant:

User-agent: Synapse-PT-HttpComponents-NIO
Disallow: /

However, it's important to note that malicious bots using these user agents often ignore robots.txt rules. If you're experiencing suspicious traffic, you may need to implement more robust blocking measures through your web server configuration or web application firewall.

For Apache-based servers, you can add rules to your .htaccess file to block requests with these user agents. In Nginx, similar rules can be added to your server configuration. Many content management systems and security plugins also provide interfaces for blocking specific user agents.

If you're working with legitimate Azure Synapse Analytics integrations, blocking should be handled through proper authentication and authorization mechanisms rather than user agent filtering, as these are typically authenticated service connections rather than web crawlers.