CVE-2026-18905 in ContextForge MCP Gateway
Summary
by MITRE • 09/04/2026
IBM ContextForge MCP Gateway (`mcp-contextforge-gateway`) <= v1.0.6 MCP Context Forge could allow a remote authenticated attacker to obtain sensitive information due to a DNS rebinding vulnerability during tool invocation.
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Analysis
by VulDB Data Team • 09/04/2026
The IBM ContextForge MCP Gateway, specifically versions up to and including 1.0.6, contains a critical security flaw classified as a DNS rebinding vulnerability that affects the integrity of internal service communications. This vulnerability arises from insufficient validation mechanisms within the gateway when processing tool invocations initiated by authenticated users. The core technical issue lies in the application's handling of domain name resolution during runtime operations. When an attacker provides a maliciously crafted hostname for a target resource, the system resolves this name to its corresponding IP address without adequately verifying whether that address belongs to a trusted internal network segment or if it has been dynamically bound by an external entity through DNS manipulation techniques.
DNS rebinding is a sophisticated attack vector where an adversary controls a domain and configures its DNS records to point to an internal private IP address, such as those found in local area networks or cloud provider metadata services. By exploiting the browser's same-origin policy limitations or similar trust boundaries within server-side proxying mechanisms, the attacker can trick the gateway into treating external-controlled domains as trusted internal endpoints. In this specific context, when a user invokes a tool that requires fetching data from an external source specified by hostname, the vulnerable version of ContextForge resolves the provided domain and proceeds to make requests against it without checking if the resolved IP address falls within allowed ranges or is distinct from public internet addresses. This lack of strict allow-listing for internal resources allows the gateway to act as a proxy for arbitrary network connections on behalf of the authenticated user.
The operational impact of this vulnerability is significant, primarily enabling unauthorized access to sensitive information residing behind firewalls that would otherwise be inaccessible from the public internet. An attacker who has obtained valid authentication credentials can leverage this flaw to probe internal services, exfiltrate data from cloud metadata endpoints which often contain instance identities and temporary security tokens, or interact with other backend systems such as databases, administrative consoles, or microservices running on non-public ports. This effectively bypasses network-level perimeter defenses because the traffic appears to originate from a trusted gateway server rather than an external source. The ability to access these internal resources can lead to further compromise of the broader infrastructure, including potential privilege escalation if sensitive credentials are retrieved from metadata services or configuration files accessible via the rebinding attack path.
This vulnerability aligns with CWE-20 Improper Input Validation and specifically relates to CWE-918 Server-Side Request Forgery (SSRF) variants where DNS resolution is not properly constrained. From a threat modeling perspective, particularly within the MITRE ATT&CK framework, this behavior corresponds to Tactic TA0001 Initial Access or TA0005 Defense Evasion depending on how it is leveraged for lateral movement, and Technique T1071 Application Layer Protocol if used to tunnel data. The lack of validation against DNS rebinding attacks represents a common oversight in systems that proxy requests based on user-supplied hostnames without implementing robust IP address verification post-resolution.
To mitigate this risk, organizations running IBM ContextForge MCP Gateway should immediately upgrade to version 1.0.7 or later where the issue has been addressed through enhanced input validation and stricter network boundary enforcement. In environments where upgrading is not immediately feasible, administrators can implement compensating controls such as configuring reverse proxies with strict allow-lists for outbound connections, ensuring that DNS resolution occurs in a sandboxed environment isolated from internal networks, or deploying web application firewalls capable of detecting anomalous DNS patterns associated with rebinding attacks. Additionally, restricting the gateway's network permissions to only communicate with explicitly defined and whitelisted IP addresses can prevent exploitation even if the vulnerability remains present. Regular security audits focusing on SSRF prevention strategies are recommended for all systems that process user-supplied URLs or hostnames in server-side contexts.