CVE-2026-52001 in mcp-remote
Summary
by MITRE • 09/24/2026
An issue in geelen mcp-remote 0.1.18 through 0.1.38 allows a remote attacker to obtain sensitive information via the SSE transport eventSourceInit fetch wrapper " src/lib/utils.ts
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Analysis
by VulDB Data Team • 09/24/2026
The vulnerability identified in geelen mcp-remote versions 0.1.18 through 0.1.38 represents a significant security flaw within the server-sent events (SSE) implementation, specifically located in the transport layer's fetch wrapper utility found at src/lib/utils.ts. This component is responsible for managing the initialization and configuration of HTTP requests used to establish persistent connections with remote servers. The core issue stems from an improper handling or exposure of sensitive data during the setup phase of these event streams. When a client initiates a connection, the application processes various parameters intended to configure the underlying fetch API call. Due to insufficient sanitization or validation logic within this wrapper, certain internal states, configuration details, or potentially authentication tokens can be inadvertently exposed through the SSE transport mechanism. This exposure allows an external actor who has network access to intercept and extract information that was not designed for public consumption, thereby compromising the confidentiality of the communication channel.
From a technical perspective, this flaw aligns with CWE-209, which describes the generation of error messages containing sensitive information, or more broadly with CWE-200, where an attacker gains access to critical system resources without authorization. The vulnerability exploits the trust placed in the transport layer by assuming that internal utility functions will not leak state data when interacting with remote endpoints. In modern web architectures relying on SSE for real-time updates, maintaining strict separation between control plane metadata and user-facing event payloads is essential. Here, the boundary appears blurred, allowing an attacker to leverage standard HTTP request/response patterns or WebSocket-like behaviors inherent in SSE implementations to probe for leaked headers, cookies, or internal routing information that could facilitate further attacks such as session hijacking or privilege escalation if combined with other vulnerabilities.
The operational impact of this vulnerability is primarily centered on data confidentiality and potential downstream exploitation risks. While the immediate effect may appear limited to informational disclosure, the leakage of sensitive configuration details can provide attackers with valuable intelligence about the target environment's architecture, authentication mechanisms, or internal service endpoints. This information gathering phase is critical in attack chains as defined by MITRE ATT&CK technique T1078, Valid Accounts, if credentials are exposed, or T1539, Steal Web Session Cookie, if session tokens are leaked. Furthermore, knowledge of internal API structures can aid an attacker in crafting more precise malicious payloads for subsequent injection attacks against the application's backend services. For organizations deploying geelen mcp-remote in production environments, this vulnerability undermines trust in secure communications and may violate compliance requirements related to data protection standards such as GDPR or HIPAA if personal identifiable information is inadvertently transmitted through these exposed channels.
To mitigate this risk, immediate action should be taken by upgrading the geelen mcp-remote package to a version beyond 0.1.38 where the issue has been resolved in subsequent releases. Developers must ensure that their dependency management systems are configured to automatically check for and apply security patches related to SSE transport layers. In cases where an upgrade is not immediately feasible, implementing network-level controls such as strict firewall rules or Web Application Firewalls (WAF) can help monitor and filter anomalous traffic patterns associated with probing for sensitive data leaks. Additionally, code reviews focusing on the src/lib/utils.ts file should be conducted to verify that all fetch wrapper configurations explicitly strip out non-essential headers and internal state variables before transmission. Adopting a defense-in-depth strategy by validating input parameters and enforcing least privilege principles in transport layer implementations will significantly reduce the attack surface associated with real-time communication protocols.