CVE-2026-61568 in gitlab-mcp
Summary
by MITRE • 09/16/2026
`@zereight/mcp-gitlab` is a Model Context Protocol server for GitLab. Versions prior to 2.1.30 expose the Streamable HTTP MCP endpoint without an effective Host or Origin allowlist. A malicious web page can use DNS rebinding to route browser requests to a victim's local MCP listener while preserving an attacker-controlled `Host` and `Origin`. The server accepts those headers and reaches the MCP initialization path instead of rejecting the request at the HTTP boundary. Version 2.1.30 contains a patch.
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Analysis
by VulDB Data Team • 09/16/2026
The vulnerability identified in @zereight/mcp-gitlab versions prior to 2.1.30 represents a critical security flaw rooted in insufficient validation of incoming HTTP headers, specifically regarding Host and Origin fields within the Streamable HTTP Model Context Protocol endpoint. This architectural weakness allows for DNS rebinding attacks where an attacker can manipulate domain resolution to direct browser-based requests toward a victim's local MCP listener while simultaneously preserving attacker-controlled values for the Host and Origin headers. By bypassing standard cross-origin checks that rely on these header values, malicious web pages can successfully interact with internal services that are typically isolated from external network access or restricted by same-origin policies.
From a technical perspective, the core issue lies in the server's failure to enforce an effective allowlist for Host and Origin headers before processing requests at the application layer. Instead of rejecting malformed or unauthorized cross-origin traffic at the HTTP boundary, the server proceeds to accept these requests and routes them into the MCP initialization path. This behavior effectively neutralizes browser security mechanisms designed to prevent unauthorized access to local resources, as the victim's browser believes it is communicating with a trusted origin due to the spoofed headers facilitated by DNS rebinding techniques. The lack of strict validation allows an attacker to exploit this trust relationship to execute arbitrary commands or extract sensitive data from the GitLab instance managed through the MCP server.
The operational impact of this vulnerability is severe, as it enables remote attackers to bypass network-level isolation and interact directly with local development tools and version control systems. An exploited system may suffer unauthorized access to repositories, exposure of private codebases, potential injection of malicious commits, or exfiltration of sensitive configuration data stored within the GitLab environment. Since Model Context Protocol servers often act as bridges between AI models and external APIs, this breach could also facilitate broader supply chain attacks if the compromised MCP server is used to feed poisoned context into automated development workflows. The ability to spoof headers means that traditional perimeter defenses are rendered ineffective against locally hosted instances exposed via loopback interfaces or local network segments accessible through DNS manipulation.
To mitigate this risk, organizations must immediately upgrade @zereight/mcp-gitlab to version 2.1.30 or later, which contains the necessary patches for header validation and origin checking. In environments where upgrading is not immediately feasible, administrators should implement strict firewall rules to restrict access to the MCP endpoint exclusively from trusted IP addresses rather than relying on browser-based security controls alone. Additionally, deploying reverse proxies with rigorous request filtering can help enforce correct Host headers and block requests originating from untrusted domains or containing suspicious DNS resolution patterns associated with rebinding attacks. Continuous monitoring of HTTP logs for anomalous origin values and implementing Content Security Policy directives that restrict WebSocket or Streamable HTTP connections to known safe origins further reduces the attack surface.
This vulnerability aligns with CWE-346, which describes the improper verification of a reference against an expected entry point, as well as CWE-918 regarding Server-Side Request Forgery (SSRF) variants where internal resources are accessed via manipulated headers. In terms of MITRE ATT&CK framework classification, this exploit leverages T1071 Application Layer Protocol for communication and potentially T1564 Hidden Files and Directories if the attacker uses local network access to evade detection. The failure to validate Host and Origin headers constitutes a significant deviation from secure coding practices recommended by OWASP for web application security, particularly in services that expose internal APIs through public-facing or locally accessible endpoints. Ensuring strict input validation at every layer of the request processing pipeline is essential to prevent such bypasses and maintain the integrity of local development infrastructure.