CVE-2026-34756

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An unauthenticated attacker can exploit this vulnerability by sending a specially crafted HTTP request with an excessively large 'n' parameter to the vLLM OpenAI-compatible API server. 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{"bugzilla": {"description": "vllm: vLLM: Denial of Service via excessively large 'n' parameter in OpenAI-compatible API", "id": "2455425", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2455425"}, "csaw": false, "cvss3": {"cvss3_base_score": "6.5", "cvss3_scoring_vector": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "status": "draft"}, "cwe": "CWE-1284", "details": ["A flaw was found in vLLM, an inference and serving engine for large language models (LLMs). An unauthenticated attacker can exploit this vulnerability by sending a specially crafted HTTP request with an excessively large 'n' parameter to the vLLM OpenAI-compatible API server. This can lead to a Denial of Service (DoS) by consuming excessive memory and blocking the system's event loop, causing the server to crash."], "mitigation": {"lang": "en:us", "value": "Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability."}, "name": "CVE-2026-34756", "package_state": [{"cpe": "cpe:/a:redhat:ai_inference_server:3", "fix_state": "Fix deferred", "package_name": "rhaiis-preview/vllm-cuda-rhel9", "product_name": "Red Hat AI Inference Server"}, {"cpe": "cpe:/a:redhat:ai_inference_server:3", "fix_state": "Fix deferred", "package_name": "rhaiis/vllm-cpu-rhel9", "product_name": "Red Hat AI Inference Server"}, {"cpe": "cpe:/a:redhat:ai_inference_server:3", "fix_state": "Fix deferred", "package_name": "rhaiis/vllm-cuda-rhel9", "product_name": "Red Hat AI Inference Server"}, {"cpe": "cpe:/a:redhat:ai_inference_server:3", "fix_state": "Fix deferred", "package_name": "rhaiis/vllm-neuron-rhel9", "product_name": "Red Hat AI Inference Server"}, {"cpe": "cpe:/a:redhat:ai_inference_server:3", "fix_state": "Fix deferred", "package_name": "rhaiis/vllm-rocm-rhel9", "product_name": "Red Hat AI Inference Server"}, {"cpe": "cpe:/a:redhat:ai_inference_server:3", "fix_state": "Fix deferred", "package_name": "rhaiis/vllm-spyre-rhel9", "product_name": "Red Hat AI Inference Server"}, {"cpe": "cpe:/a:redhat:ai_inference_server:3", "fix_state": "Fix deferred", "package_name": "rhaiis/vllm-tpu-rhel9", "product_name": "Red Hat AI Inference Server"}, {"cpe": "cpe:/a:redhat:enterprise_linux_ai:3", "fix_state": "Fix deferred", "package_name": "rhelai3/bootc-aws-cuda-rhel9", "product_name": "Red Hat Enterprise Linux AI (RHEL AI) 3"}, {"cpe": "cpe:/a:redhat:enterprise_linux_ai:3", "fix_state": "Fix deferred", "package_name": "rhelai3/bootc-azure-cuda-rhel9", "product_name": "Red Hat Enterprise Linux AI (RHEL AI) 3"}, {"cpe": "cpe:/a:redhat:enterprise_linux_ai:3", "fix_state": "Fix deferred", "package_name": "rhelai3/bootc-azure-rocm-rhel9", "product_name": "Red Hat Enterprise Linux AI (RHEL AI) 3"}, {"cpe": "cpe:/a:redhat:enterprise_linux_ai:3", "fix_state": "Fix deferred", "package_name": "rhelai3/bootc-cuda-rhel9", "product_name": "Red Hat Enterprise Linux AI (RHEL AI) 3"}, {"cpe": "cpe:/a:redhat:enterprise_linux_ai:3", "fix_state": "Fix deferred", "package_name": "rhelai3/bootc-gcp-cuda-rhel9", "product_name": "Red Hat Enterprise Linux AI (RHEL AI) 3"}, {"cpe": "cpe:/a:redhat:enterprise_linux_ai:3", "fix_state": "Fix deferred", "package_name": "rhelai3/bootc-rocm-rhel9", "product_name": "Red Hat Enterprise Linux AI (RHEL AI) 3"}, {"cpe": "cpe:/a:redhat:openshift_ai", "fix_state": "Fix deferred", "package_name": "rhoai/odh-kserve-agent-rhel9", "product_name": "Red Hat OpenShift AI (RHOAI)"}, {"cpe": "cpe:/a:redhat:openshift_ai", "fix_state": "Fix deferred", "package_name": "rhoai/odh-kserve-controller-rhel9", "product_name": "Red Hat OpenShift AI (RHOAI)"}, {"cpe": "cpe:/a:redhat:openshift_ai", "fix_state": "Fix deferred", "package_name": "rhoai/odh-kserve-router-rhel9", "product_name": "Red Hat OpenShift AI (RHOAI)"}, {"cpe": "cpe:/a:redhat:openshift_ai", "fix_state": "Fix deferred", "package_name": "rhoai/odh-kserve-storage-initializer-rhel9", "product_name": "Red Hat OpenShift AI (RHOAI)"}, {"cpe": "cpe:/a:redhat:openshift_ai", "fix_state": "Fix deferred", "package_name": "rhoai/odh-vllm-cpu-rhel9", "product_name": "Red Hat OpenShift AI (RHOAI)"}, {"cpe": "cpe:/a:redhat:openshift_ai", "fix_state": "Fix deferred", "package_name": "rhoai/odh-vllm-cuda-rhel9", "product_name": "Red Hat OpenShift AI (RHOAI)"}, {"cpe": "cpe:/a:redhat:openshift_ai", "fix_state": "Fix deferred", "package_name": "rhoai/odh-vllm-gaudi-rhel9", "product_name": "Red Hat OpenShift AI (RHOAI)"}, {"cpe": "cpe:/a:redhat:openshift_ai", "fix_state": "Fix deferred", "package_name": "rhoai/odh-vllm-rocm-rhel9", "product_name": "Red Hat OpenShift AI (RHOAI)"}], "public_date": "2026-04-06T15:40:03Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-34756\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-34756\nhttps://github.com/vllm-project/vllm/commit/b111f8a61f100fdca08706f41f29ef3548de7380\nhttps://github.com/vllm-project/vllm/pull/37952\nhttps://github.com/vllm-project/vllm/security/advisories/GHSA-3mwp-wvh9-7528"], "threat_severity": "Important"}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[0.1.0,0.19.0)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "vllm", "source": "cna", "vendor": "vllm-project"}, "product": "vllm", "vendor": "vllm-project"}], "analysis": {"en": {"generated_at": "2026-04-07T01:43:55.944918+00:00", "value": {"mitigation_remediation": ["Upgrade vLLM to version 0.19.0 or newer, which includes the bound validation for the 'n' parameter.", "If an immediate upgrade is not possible, restrict external access to the OpenAI-compatible API endpoint to trusted internal networks or apply firewall rules to block requests from untrusted sources.", "As a temporary safeguard, implement application\u2011level rate limiting or a reverse\u2011proxy that enforces a maximum 'n' value to prevent oversized requests from reaching the server.", "Continuously monitor request logs for unusually large 'n' values and be prepared to restart the service quickly if an OOM event occurs."], "summary": {"action": "Immediate Patch", "impact": "Denial of Service via Out\u2011of\u2011Memory crash"}, "threat_synthesis": {"affected_systems": "Affected instances are vLLM deployments using versions from 0.1.0 up through 0.18.x. The issue is resolved in vLLM 0.19.0 and later. The affected product is the vllm-project vllm inference and serving engine for large language models.", "description_and_impact": "The vulnerability stems from the lack of an upper bound on the 'n' parameter in vLLM's OpenAI-compatible API server. An unauthenticated attacker can send a request with an astronomically large 'n' value, causing the server to allocate millions of request objects and exhaust memory before the request reaches the scheduling queue. This leads to an immediate Out\u2011of\u2011Memory crash and blocks the Python asyncio event loop, effectively denying service to all clients.", "risk_and_exploitability": "The CVSS score of 6.5 classifies the vulnerability as moderate severity, with a strong impact on availability and no authentication required. The EPSS score is not available, so the exploitation likelihood cannot be quantified, and the vulnerability is not listed in the CISA KEV catalog. Based on the description it is inferred that the attack vector is remote, performed by sending an unauthenticated HTTP request to the API server's completion endpoint."}}}}, "created": "2026-04-06T20:13:54.001503+00:00", "updated": "2026-04-07T06:54:58.517016+00:00", "vendors": ["vllm-project", "vllm-project$PRODUCT$vllm"]}