Server-Side Request Forgery in Eclipse Theia

Mitigation Strategies

Immediate mitigation steps include restricting access to the /services/request-service RPC endpoint to trusted users only.

Additional measures involve validating or allowlisting destination URLs to prevent server-side requests to unauthorized internal resources.

Network-level controls such as firewall rules or proxy configurations should be used to block or limit outbound HTTP requests from the backend to internal or localhost addresses.

Blocking the RPC endpoint at the proxy layer or restricting network access to the backend service can also reduce exposure.

Upgrading Eclipse Theia to version 1.73.0 or later, where the vulnerability is patched, is a recommended long-term solution.

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Executive Summary

CVE-2026-10055 is a Server-Side Request Forgery (SSRF) vulnerability in Eclipse Theia versions 1.26.0 and above. The backend /services/request-service RPC accepts a URL from any client connected to the standard /services messaging endpoint and performs the HTTP request server-side without validating or allowlisting the destination URL.

This allows an attacker with access to the Theia service connection to make the backend fetch and return responses from internal or localhost services that are normally inaccessible from the browser, exposing sensitive internal resources.

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Impact Analysis

This vulnerability can lead to unauthorized access to internal administrative endpoints, cloud instance metadata services, and other sensitive internal resources that should be protected from untrusted users.

An attacker with low privileges and no user interaction can exploit this to read confidential information by making the backend server perform HTTP requests to internal services and returning their full response bodies.

This is especially dangerous in multi-tenant or publicly accessible Theia deployments where untrusted users can reach the backend service connection.

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Detection Guidance

Detection of this vulnerability involves monitoring for unusual or unauthorized requests to the /services/request-service RPC endpoint in Eclipse Theia deployments.

Specifically, look for HTTP requests sent to the backend that include attacker-controlled URLs targeting localhost or internal services.

Commands to detect potential exploitation attempts could include inspecting network traffic or logs for requests to /services/request-service with suspicious URL parameters.

• Use network monitoring tools like tcpdump or Wireshark to capture traffic to the Theia service endpoint and filter for requests containing /services/request-service.
• Example tcpdump command: tcpdump -i <interface> -A 'tcp port 80 or tcp port 443' | grep '/services/request-service'
• Check Theia server logs for RPC calls to /services/request-service with URLs pointing to localhost or internal IP ranges.

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Compliance Impact

This vulnerability allows unauthorized access to internal resources and sensitive data by exposing internal administrative endpoints, cloud instance metadata services, and other protected resources through server-side request forgery (SSRF).

Such unauthorized data exposure can lead to violations of data protection regulations and standards like GDPR and HIPAA, which require strict controls on access to sensitive and personal data.

Because the vulnerability enables attackers to retrieve sensitive internal information without proper authorization, affected deployments may face compliance risks related to confidentiality and data protection requirements.

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