The vulnerability allows an authenticated API client to send GenerateResponse objects that are decoded without enforcing maximum response size or token limits. This permits the client to cause the server to consume excessive CPU and memory, resulting in large or unlimited responses, which can lead to denial of service or resource exhaustion.

The issue affects the vllm-project vllm inference engine before version 0.26.0. All releases prior to 0.26.0 are vulnerable; later releases contain the fix.

The CVSS score of 4.3 denotes a moderate severity. The EPSS score is not available and the vulnerability is not listed in the CISA KEV catalog, suggesting a lower immediate exploitation risk. However, because the flaw is triggered only by an authenticated user sending a specially crafted request to the derender endpoints, the attack requires valid credentials. The lack of output size checks means an attacker can drain server resources and potentially disrupt service availability within a single authenticated session.