CVE-2026-53509 in ckan-mcp-server
Summary
by MITRE • 08/21/2026
CKAN MCP Server is a tool for querying CKAN open data portals. A known vulnerability CVE-2026-33060 indicated tools including ckan_package_search and sparql_query that accept a base_url parameter had the risk of making HTTP requests to arbitrary endpoints without restriction. A fix was applied to filter out ip addresses. However, a method to bypass exists prior to version 0.4.106. CKAN MCP Server validates caller-supplied CKAN server URLs by inspecting only the parsed hostname string before issuing outbound HTTP requests. In `src/utils/http.ts`, hostname aliases such as `ip6-localhost` are not equal to `localhost`, are not dotted IPv4 literals, and are not bracketed IPv6 literals, so they pass the SSRF filter but can resolve to loopback when the server performs the request. A remote MCP caller that can invoke CKAN tools with a `server_url` can therefore make the server connect to local or private addresses and, for CKAN-shaped responses, receive response-derived data. The updated fix in version 0.4.106 replaced the single `hostname === 'localhost'` check with a blocked-hostname `Set` covering `ip6-localhost` and `ip6-loopback`.
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Analysis
by VulDB Data Team • 08/21/2026
The vulnerability identified as CVE-2026-33060 represents a Server-Side Request Forgery (SSRF) flaw within the CKAN MCP Server, specifically affecting versions prior to 0.4.106. This tool serves as an interface for querying open data portals hosted on CKAN instances, allowing remote Model Context Protocol callers to execute tools such as ckan_package_search and sparql_query. These tools accept a base_url parameter that dictates the target server from which data is retrieved. The core technical flaw lies in the validation logic implemented within the src/utils/http.ts module, where the application attempts to restrict outbound HTTP requests to prevent access to internal or private network resources. However, the initial mitigation strategy relied on an insufficient check that only compared the parsed hostname string against a literal value of localhost. This approach failed to account for alternative DNS representations and aliases that resolve to loopback interfaces but do not match the exact string comparison performed by the developers.
The operational mechanism of this vulnerability exploits how domain name resolution interacts with strict string matching. The validation logic explicitly filters out dotted IPv4 literals, such as 127.0.0.1, and bracketed IPv6 literals, ensuring those specific formats are blocked. It also checks for equality against the hostname localhost. However, it neglects to consider other valid DNS aliases that map to the loopback address, most notably ip6-localhost and ip6-loopback. When a remote attacker supplies one of these alternative hostnames as part of the server_url parameter, the validation function returns true because the string does not match the blocked patterns or the localhost literal. Consequently, the HTTP client proceeds to resolve the hostname via standard DNS resolution mechanisms. Since ip6-localhost is configured in most modern operating systems' hosts files and DNS resolvers to point to 127.0.0.1 ::1, the resulting network connection targets the local machine rather than an external server. This allows a remote attacker to force the CKAN MCP Server to initiate connections to internal services that are otherwise inaccessible from the public internet.
The impact of this SSRF vulnerability is significant for environments where the CKAN instance has access to sensitive internal infrastructure, such as metadata databases, administrative interfaces, or other microservices running on localhost or private network ranges. An attacker can leverage this flaw to probe internal networks, potentially extracting data from services that respond with HTTP traffic compatible with CKAN response formats. This could lead to unauthorized disclosure of confidential information stored within the local environment. Furthermore, if the underlying server is configured to follow redirects or supports other protocols beyond standard HTTP GET requests, the scope of potential exploitation expands further, although the primary risk remains focused on data exfiltration through SSRF-induced internal queries. The vulnerability aligns with CWE-918, which describes Server-Side Request Forgery flaws resulting from insufficient validation of user-supplied URLs or hostnames.
To mitigate this issue, organizations must upgrade to CKAN MCP Server version 0.4.106 or later, where the developers have addressed the gap by replacing the single hostname equality check with a comprehensive blocked-hostname Set that explicitly includes ip6-localhost and ip6-loopback alongside localhost. This ensures that all common aliases for loopback addresses are rejected before any DNS resolution occurs. In addition to upgrading, security teams should implement defense-in-depth strategies such as network segmentation to isolate CKAN servers from critical internal services. Utilizing a web application firewall or reverse proxy with strict egress filtering can also prevent outbound connections to private IP ranges and localhost regardless of the application-level validation logic. Monitoring for unusual outbound connection patterns originating from the MCP server host can aid in detecting potential exploitation attempts before significant data loss occurs. This incident highlights the importance of validating not just literal string matches but all possible DNS representations of restricted addresses when implementing SSRF protections, a principle often referenced in ATT&CK technique T1598, specifically regarding phishing and social engineering vectors that might be used to trick users into configuring malicious server URLs within trusted tools.