CVE-2026-115917 in vLLM
Summary
by MITRE • 10/26/2026
vLLM is an inference and serving engine for large language models. Prior to 0.32.0, the OpenAI-compatible server configures Starlette CORSMiddleware with allowed_origins set to a wildcard by default. A malicious web page can use a victim's browser to reach an unauthenticated vLLM server on localhost, an internal network, or a VPN, call endpoints including GET /v1/models and POST /v1/chat/completions, consume GPU resources, and read responses. Cookie-based cross-site request forgery does not apply because credentials are disabled by default, and deployments requiring bearer authentication are exposed only when the caller already has a usable token. This issue is fixed in version 0.32.0.
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Analysis
by VulDB Data Team • 10/26/2026
The vulnerability identified in vLLM versions prior to 0.32.0 stems from an overly permissive Cross-Origin Resource Sharing configuration within its OpenAI-compatible server interface. Specifically, the application utilizes Starlette's CORSMiddleware with the allowed_origins parameter set to a wildcard value by default. This misconfiguration effectively disables origin validation for HTTP requests originating from web browsers, allowing any website loaded in a user's browser to make cross-origin API calls to the vLLM instance without restriction. The core technical flaw lies not in an authentication bypass per se, but in the failure to restrict which origins are permitted to interact with the service via standard web protocols, thereby exposing internal or localhost-bound services to public internet traffic if network access is available.
From a security architecture perspective, this configuration creates a significant exposure surface for unauthenticated interactions when the server is bound to 0.0.0.0 or accessible from external networks. Although cookie-based cross-site request forgery attacks are mitigated because credentials such as cookies are disabled by default in these deployments, the lack of origin checks allows malicious web pages to leverage the victim's browser context to send requests directly to the API endpoints. This means that any user who visits a crafted webpage while having an active session or network path to the vLLM server can trigger actions on their behalf without explicit consent, relying solely on the browser's automatic inclusion of certain headers and the permissive CORS policy.
The operational impact of this vulnerability is substantial for organizations deploying large language models via vLLM in production or testing environments that are inadvertently exposed. An attacker can exploit this to consume significant GPU resources by sending repeated inference requests through endpoints such as GET /v1/models and POST /v1/chat/completions. This resource exhaustion can lead to denial of service conditions, increasing infrastructure costs and degrading performance for legitimate users. Furthermore, the ability to read responses from these endpoints allows attackers to extract sensitive data processed or generated by the model, potentially leading to information disclosure if the inputs contained proprietary or personal data that is reflected in the output.
This vulnerability aligns with CWE-942, which describes Permissive Cross-domain Policy with Untrusted Domains, as it permits cross-origin requests from any source without adequate verification of intent or origin legitimacy. In terms of attack vectors, this scenario maps to ATT&CK technique T1505.003, Server Software Component: Web Shell, although in this context the exploitation is more akin to unauthorized API access via web-based interactions rather than a traditional shell. It also relates to CWE-284, Improper Access Control, because the default configuration fails to enforce appropriate restrictions on who can interact with the service through browser-mediated requests.
To mitigate this risk, organizations must upgrade vLLM to version 0.32.0 or later where the CORS middleware is configured more restrictively by default. For deployments that cannot immediately upgrade, administrators should manually configure the allowed_origins parameter in the server settings to explicitly list trusted domains rather than using a wildcard. Additionally, binding the service to localhost only and ensuring it is not exposed to external networks via firewalls or reverse proxies provides an essential layer of defense-in-depth. Implementing proper network segmentation ensures that even if CORS restrictions are bypassed, the underlying API remains inaccessible from untrusted environments.