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6.5
MEDIUM CVSS 3.1
CVE-2026-34756
vLLM Affected by Unauthenticated OOM Denial of Service via Unbounded `n` Parameter in OpenAI API Server
Overview
Description

vLLM is an inference and serving engine for large language models (LLMs). From 0.1.0 to before 0.19.0, a Denial of Service vulnerability exists in the vLLM OpenAI-compatible API server. Due to the lack of an upper bound validation on the n parameter in the ChatCompletionRequest and CompletionRequest Pydantic models, an unauthenticated attacker can send a single HTTP request with an astronomically large n value. This completely blocks the Python asyncio event loop and causes immediate Out-Of-Memory crashes by allocating millions of request object copies in the heap before the request even reaches the scheduling queue. This vulnerability is fixed in 0.19.0.

Details
INFO

Published Date :

April 6, 2026, 4:16 p.m.

Last Modified :

July 15, 2026, 2:20 a.m.

Remotely Exploit :

Yes !

Source :

[email protected]
Impact
Affected Products

The following products are affected by CVE-2026-34756 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

ID Vendor Product Action
1 Vllm-project vllm
1 Vllm vllm
: Total Affected Vendor : 2 | Products : 2
Scoring
CVSS Scores
The Common Vulnerability Scoring System is a standardized framework for assessing the severity of vulnerabilities in software and systems. We collect and displays CVSS scores from various sources for each CVE.
Score Version Severity Vector Exploitability Score Impact Score Source
CVSS 134c704f-9b21-4f2e-91b3-4a467353bcc0
CVSS 3.1 MEDIUM [email protected]
CVSS 3.1 MEDIUM 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Solution
Update vLLM to version 0.19.0 or later to fix the denial-of-service vulnerability.
  • Update vLLM to version 0.19.0 or later.
  • Validate the n parameter upper bound in API requests.
References
References to Advisories, Solutions, and Tools

Here, you will find a curated list of external links that provide in-depth information, practical solutions, and valuable tools related to CVE-2026-34756.

URL Resource
https://github.com/vllm-project/vllm/commit/b111f8a61f100fdca08706f41f29ef3548de7380 Patch
https://github.com/vllm-project/vllm/pull/37952 Issue Tracking Patch
https://github.com/vllm-project/vllm/security/advisories/GHSA-3mwp-wvh9-7528 Patch Vendor Advisory
https://access.redhat.com/errata/RHSA-2026:36005
https://access.redhat.com/errata/RHSA-2026:36006
https://access.redhat.com/security/cve/CVE-2026-34756
https://bugzilla.redhat.com/show_bug.cgi?id=2455425
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34756.json
CWE - Common Weakness Enumeration

While CVE identifies specific instances of vulnerabilities, CWE categorizes the common flaws or weaknesses that can lead to vulnerabilities. CVE-2026-34756 is associated with the following CWEs:

Common Attack Pattern Enumeration and Classification (CAPEC)

Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2026-34756 weaknesses.

CAPEC-125: Flooding Flooding CAPEC-130: Excessive Allocation Excessive Allocation CAPEC-147: XML Ping of the Death XML Ping of the Death CAPEC-197: Exponential Data Expansion Exponential Data Expansion CAPEC-229: Serialized Data Parameter Blowup Serialized Data Parameter Blowup CAPEC-230: Serialized Data with Nested Payloads Serialized Data with Nested Payloads CAPEC-231: Oversized Serialized Data Payloads Oversized Serialized Data Payloads CAPEC-469: HTTP DoS HTTP DoS CAPEC-482: TCP Flood TCP Flood CAPEC-486: UDP Flood UDP Flood CAPEC-487: ICMP Flood ICMP Flood CAPEC-488: HTTP Flood HTTP Flood CAPEC-489: SSL Flood SSL Flood CAPEC-490: Amplification Amplification CAPEC-491: Quadratic Data Expansion Quadratic Data Expansion CAPEC-493: SOAP Array Blowup SOAP Array Blowup CAPEC-494: TCP Fragmentation TCP Fragmentation CAPEC-495: UDP Fragmentation UDP Fragmentation CAPEC-496: ICMP Fragmentation ICMP Fragmentation CAPEC-528: XML Flood XML Flood

We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).

Results are limited to the first 15 repositories due to potential performance issues.

The following list is the news that have been mention CVE-2026-34756 vulnerability anywhere in the article.

Results are limited to the first 20 news articles due to potential performance issues.

The following table lists the changes that have been made to the CVE-2026-34756 vulnerability over time.

Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.

  • CVE Modified by 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

    Jul. 15, 2026

    Action Type Old Value New Value
    Changed Affected [{'cpes': ['cpe:/a:redhat:ai_inference_server:3.2::el9'], 'vendor': 'Red Hat', 'product': 'Red Hat AI Inference Server 3.2', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:ai_inference_server:3'], 'vendor': 'Red Hat', 'product': 'Red Hat AI Inference Server', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:enterprise_linux_ai:3'], 'vendor': 'Red Hat', 'product': 'Red Hat Enterprise Linux AI (RHEL AI) 3', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_ai'], 'vendor': 'Red Hat', 'product': 'Red Hat OpenShift AI (RHOAI)', 'defaultStatus': 'affected'}] [{'cpes': ['cpe:/a:redhat:ai_inference_server:3.2::el9'], 'vendor': 'Red Hat', 'product': 'Red Hat AI Inference Server 3.2', 'versions': [{'status': 'unaffected', 'version': '1782951012', 'lessThan': '*', 'versionType': 'rpm'}], 'packageName': 'rhaiis/vllm-cuda-rhel9', 'collectionURL': 'https://catalog.redhat.com/software/containers/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:ai_inference_server:3.2::el9'], 'vendor': 'Red Hat', 'product': 'Red Hat AI Inference Server 3.2', 'versions': [{'status': 'unaffected', 'version': '1782951244', 'lessThan': '*', 'versionType': 'rpm'}], 'packageName': 'rhaiis/vllm-rocm-rhel9', 'collectionURL': 'https://catalog.redhat.com/software/containers/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:ai_inference_server:3'], 'vendor': 'Red Hat', 'product': 'Red Hat AI Inference Server', 'packageName': 'rhaiis/vllm-cpu-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:ai_inference_server:3'], 'vendor': 'Red Hat', 'product': 'Red Hat AI Inference Server', 'packageName': 'rhaiis/vllm-neuron-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:ai_inference_server:3'], 'vendor': 'Red Hat', 'product': 'Red Hat AI Inference Server', 'packageName': 'rhaiis/vllm-spyre-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:ai_inference_server:3'], 'vendor': 'Red Hat', 'product': 'Red Hat AI Inference Server', 'packageName': 'rhaiis/vllm-tpu-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:enterprise_linux_ai:3'], 'vendor': 'Red Hat', 'product': 'Red Hat Enterprise Linux AI (RHEL AI) 3', 'packageName': 'rhelai3/bootc-aws-cuda-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:enterprise_linux_ai:3'], 'vendor': 'Red Hat', 'product': 'Red Hat Enterprise Linux AI (RHEL AI) 3', 'packageName': 'rhelai3/bootc-azure-cuda-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:enterprise_linux_ai:3'], 'vendor': 'Red Hat', 'product': 'Red Hat Enterprise Linux AI (RHEL AI) 3', 'packageName': 'rhelai3/bootc-azure-rocm-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:enterprise_linux_ai:3'], 'vendor': 'Red Hat', 'product': 'Red Hat Enterprise Linux AI (RHEL AI) 3', 'packageName': 'rhelai3/bootc-cuda-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:enterprise_linux_ai:3'], 'vendor': 'Red Hat', 'product': 'Red Hat Enterprise Linux AI (RHEL AI) 3', 'packageName': 'rhelai3/bootc-gcp-cuda-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:enterprise_linux_ai:3'], 'vendor': 'Red Hat', 'product': 'Red Hat Enterprise Linux AI (RHEL AI) 3', 'packageName': 'rhelai3/bootc-rocm-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_ai'], 'vendor': 'Red Hat', 'product': 'Red Hat OpenShift AI (RHOAI)', 'packageName': 'rhoai/odh-kserve-agent-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_ai'], 'vendor': 'Red Hat', 'product': 'Red Hat OpenShift AI (RHOAI)', 'packageName': 'rhoai/odh-kserve-controller-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_ai'], 'vendor': 'Red Hat', 'product': 'Red Hat OpenShift AI (RHOAI)', 'packageName': 'rhoai/odh-kserve-router-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_ai'], 'vendor': 'Red Hat', 'product': 'Red Hat OpenShift AI (RHOAI)', 'packageName': 'rhoai/odh-kserve-storage-initializer-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_ai'], 'vendor': 'Red Hat', 'product': 'Red Hat OpenShift AI (RHOAI)', 'packageName': 'rhoai/odh-vllm-cpu-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_ai'], 'vendor': 'Red Hat', 'product': 'Red Hat OpenShift AI (RHOAI)', 'packageName': 'rhoai/odh-vllm-cuda-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_ai'], 'vendor': 'Red Hat', 'product': 'Red Hat OpenShift AI (RHOAI)', 'packageName': 'rhoai/odh-vllm-gaudi-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_ai'], 'vendor': 'Red Hat', 'product': 'Red Hat OpenShift AI (RHOAI)', 'packageName': 'rhoai/odh-vllm-rocm-rhel9', 'collectionURL': 'https://access.redhat.com/downloads/content/package-browser/', 'defaultStatus': 'affected'}]
  • CVE Modified by 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

    Jul. 07, 2026

    Action Type Old Value New Value
    Added Reference https://access.redhat.com/errata/RHSA-2026:36005
    Added Reference https://access.redhat.com/errata/RHSA-2026:36006
    Changed Affected [{'cpes': ['cpe:/a:redhat:ai_inference_server:3'], 'vendor': 'Red Hat', 'product': 'Red Hat AI Inference Server', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:enterprise_linux_ai:3'], 'vendor': 'Red Hat', 'product': 'Red Hat Enterprise Linux AI (RHEL AI) 3', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_ai'], 'vendor': 'Red Hat', 'product': 'Red Hat OpenShift AI (RHOAI)', 'defaultStatus': 'affected'}] [{'cpes': ['cpe:/a:redhat:ai_inference_server:3.2::el9'], 'vendor': 'Red Hat', 'product': 'Red Hat AI Inference Server 3.2', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:ai_inference_server:3'], 'vendor': 'Red Hat', 'product': 'Red Hat AI Inference Server', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:enterprise_linux_ai:3'], 'vendor': 'Red Hat', 'product': 'Red Hat Enterprise Linux AI (RHEL AI) 3', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_ai'], 'vendor': 'Red Hat', 'product': 'Red Hat OpenShift AI (RHOAI)', 'defaultStatus': 'affected'}]
  • CVE Modified by 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

    Jun. 30, 2026

    Action Type Old Value New Value
    Added Affected [{'cpes': ['cpe:/a:redhat:ai_inference_server:3'], 'vendor': 'Red Hat', 'product': 'Red Hat AI Inference Server', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:enterprise_linux_ai:3'], 'vendor': 'Red Hat', 'product': 'Red Hat Enterprise Linux AI (RHEL AI) 3', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_ai'], 'vendor': 'Red Hat', 'product': 'Red Hat OpenShift AI (RHOAI)', 'defaultStatus': 'affected'}]
    Added CVSS V3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
    Added CWE CWE-1284
    Added Reference https://access.redhat.com/security/cve/CVE-2026-34756
    Added Reference https://bugzilla.redhat.com/show_bug.cgi?id=2455425
    Added Reference https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34756.json
  • CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Jun. 17, 2026

    Action Type Old Value New Value
    Added SSVC {'id': 'CVE-2026-34756', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-04-07T14:16:25.517505Z'}
  • CVE Modified by [email protected]

    Jun. 17, 2026

    Action Type Old Value New Value
    Added Affected [{'vendor': 'vllm-project', 'product': 'vllm', 'versions': [{'status': 'affected', 'version': '>= 0.1.0, < 0.19.0'}]}]
  • Initial Analysis by [email protected]

    Apr. 20, 2026

    Action Type Old Value New Value
    Added CPE Configuration OR *cpe:2.3:a:vllm:vllm:*:*:*:*:*:*:*:* versions from (including) 0.1.0 up to (excluding) 0.19.0
    Added Reference Type GitHub, Inc.: https://github.com/vllm-project/vllm/commit/b111f8a61f100fdca08706f41f29ef3548de7380 Types: Patch
    Added Reference Type GitHub, Inc.: https://github.com/vllm-project/vllm/pull/37952 Types: Issue Tracking, Patch
    Added Reference Type GitHub, Inc.: https://github.com/vllm-project/vllm/security/advisories/GHSA-3mwp-wvh9-7528 Types: Patch, Vendor Advisory
  • New CVE Received by [email protected]

    Apr. 06, 2026

    Action Type Old Value New Value
    Added Description vLLM is an inference and serving engine for large language models (LLMs). From 0.1.0 to before 0.19.0, a Denial of Service vulnerability exists in the vLLM OpenAI-compatible API server. Due to the lack of an upper bound validation on the n parameter in the ChatCompletionRequest and CompletionRequest Pydantic models, an unauthenticated attacker can send a single HTTP request with an astronomically large n value. This completely blocks the Python asyncio event loop and causes immediate Out-Of-Memory crashes by allocating millions of request object copies in the heap before the request even reaches the scheduling queue. This vulnerability is fixed in 0.19.0.
    Added CVSS V3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
    Added CWE CWE-770
    Added Reference https://github.com/vllm-project/vllm/commit/b111f8a61f100fdca08706f41f29ef3548de7380
    Added Reference https://github.com/vllm-project/vllm/pull/37952
    Added Reference https://github.com/vllm-project/vllm/security/advisories/GHSA-3mwp-wvh9-7528
EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days. Following chart shows the EPSS score history of the vulnerability.
CVSS
Vulnerability Scoring Details
Base CVSS Score: 6.5
Attack Vector
Attack Complexity
Privileges Required
User Interaction
Scope
Confidentiality Impact
Integrity Impact
Availability Impact