CVE-2026-56681 in 9router
Summary
by MITRE • 09/22/2026
9Router is an AI router & token saver. Prior to 0.5.6, 9Router deployments that allow requests to reach Next.js without the sanitizing custom-server.js wrapper trust the client-supplied X-9r-Real-Ip header in src/dashboardGuard.js when isLocalRequest decides whether canAccessPublicLlmApi may skip API-key validation for /api/v1/* routes. A remote unauthenticated attacker can set X-9r-Real-Ip to 127.0.0.1 and be classified as a local client, including on the verified GET /api/v1/models route. This permits unauthorized use of the instance owner's configured LLM providers, consumption of paid credits, and enumeration of configured providers and models. This issue is fixed in version 0.5.6.
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Analysis
by VulDB Data Team • 09/22/2026
The vulnerability identified in versions of 9Router prior to 0.5.6 represents a critical authentication bypass stemming from improper trust of client-supplied input within the application's request handling logic. The core technical flaw resides in the src/dashboardGuard.js module, specifically within the isLocalRequest function which determines whether an incoming request originates from a trusted local source. This determination directly influences the canAccessPublicLlmApi decision tree, which controls access to sensitive API endpoints under the /api/v1/* path prefix. In environments where requests reach the Next.js application without being properly sanitized by the custom-server.js wrapper, the system fails to validate the origin of the X-9r-Real-Ip header. Instead of relying on robust server-side checks such as socket address verification or internal network segmentation validation, the application blindly accepts the value provided in this HTTP header field. This architectural weakness allows a remote unauthenticated attacker to manipulate their perceived identity by setting the X-9r-Real-Ip header to 127.0.0.1, which is universally recognized as the loopback address representing localhost.
By spoofing this local IP address, an external actor can successfully bypass authentication mechanisms that are designed to restrict access to certain API functionalities for unauthenticated users. Specifically, this manipulation grants unauthorized access to the GET /api/v1/models endpoint and other protected routes within the /api/v1/* namespace. The operational impact of this vulnerability is severe, as it effectively neutralizes the intended security boundary between public-facing interfaces and private administrative or functional APIs. Attackers can exploit this flaw to enumerate all configured Large Language Model providers and available models associated with the instance owner's account. This enumeration provides a comprehensive map of the victim's AI infrastructure capabilities, facilitating further reconnaissance for more targeted attacks against specific model endpoints that may have additional weaknesses or rate-limiting bypasses.
Beyond mere information disclosure, the exploitation of this vulnerability leads to significant financial and operational consequences through unauthorized consumption of resources. Since the attacker is classified as a local client with public access privileges, they can invoke LLM API calls without providing valid authentication credentials. This results in the direct consumption of paid credits allocated by the instance owner for AI processing tasks. The ability to execute arbitrary prompts against configured providers means that attackers can generate substantial costs on behalf of the victim, leading to unexpected billing spikes and potential service degradation if rate limits are exhausted or quotas are exceeded. Furthermore, this access could potentially be leveraged to abuse compute resources for malicious purposes such as generating harmful content, conducting prompt injection attacks, or training models using stolen data contexts exposed through these endpoints.
This vulnerability aligns with CWE-287 Improper Authentication and CWE-918 Server-Side Request Forgery (SSRF) principles where the server trusts client-controlled input regarding network identity without sufficient verification. In terms of MITRE ATT&CK, this behavior corresponds to T1078 Valid Accounts or more accurately T1563 Remote Service Tampering if used to alter configurations, but primarily it falls under initial access vectors involving exploitation of trusted relationships and misconfigured trust boundaries. The attack pattern is consistent with header injection techniques where metadata fields are manipulated to influence server-side logic decisions regarding authorization levels.
To mitigate this vulnerability, organizations must upgrade immediately to version 0.5.6 or later, which addresses the flawed validation logic in dashboardGuard.js. For deployments that cannot be upgraded instantly due to operational constraints, a temporary mitigation involves ensuring that all incoming requests are processed through the custom-server.js wrapper before reaching Next.js internals, as this layer is intended to sanitize and validate headers properly. Additionally, administrators should implement strict IP allowlisting at the network perimeter or reverse proxy level for any endpoints requiring local-only access, rather than relying on HTTP header values which can be trivially spoofed from external networks. It is also advisable to monitor API usage patterns for anomalies indicative of automated enumeration or excessive credit consumption, and to enforce rate limiting policies that apply uniformly regardless of perceived client identity to limit the blast radius of such exploitation attempts.