Copyright © 2012 Red Hat, Inc. All rights reserved. Important 2026-07-06T20:05:31 vllm: vLLM: Denial of Service via adversarial regular expression in structured outputs API 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H CWE-1333

vLLM is a high-throughput and memory-efficient inference and serving engine for LLMs. Prior to 0.24.0, the structured_outputs.regex API parameter passes a user-supplied regular expression string directly to the grammar compiler backends with no compilation timeout; in the xgrammar backend the string reaches the regex compiler with no guard, and in the outlines backend the validation step blocks structural issues such as lookarounds and backreferences but performs no complexity analysis, so a pattern with nested quantifiers passes all checks and causes exponential state-space expansion, allowing a single request containing an adversarial regex to hang an inference worker indefinitely and deny service. This issue is fixed in version 0.24.0.

A flaw was found in vLLM, a high-throughput and memory-efficient inference and serving engine for large language models (LLMs). A remote attacker could exploit this vulnerability by providing a specially crafted regular expression to the structured_outputs.regex API parameter. This adversarial regex, containing nested quantifiers, can cause an exponential expansion of the state-space in the grammar compiler, leading to an inference worker hanging indefinitely. This results in a Denial of Service (DoS) for the affected system.

An Important denial of service vulnerability exists in vLLM, as utilized within Red Hat AI Inference Server and Red Hat OpenShift AI. This flaw allows a remote, unauthenticated attacker to cause an inference worker to hang indefinitely by submitting a specially crafted regular expression to the structured outputs API. The absence of complexity analysis for nested quantifiers in the regex compiler leads to an exponential state-space expansion, resulting in prolonged service disruption. 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. Red Hat AI Inference Server 3.2 2026-08-31T00:00:00Z RHSA-2026:61627 rhaiis/vllm-cuda-rhel9:1787860580 Red Hat AI Inference Server 3.2 2026-08-31T00:00:00Z RHSA-2026:61629 rhaiis/vllm-rocm-rhel9:1787884873 Red Hat AI Inference Server 3.3 2026-08-26T00:00:00Z RHSA-2026:60363 rhaiis/vllm-spyre-rhel9:1787161776 Red Hat AI Inference Server 3.4 2026-09-21T00:00:00Z RHSA-2026:69464 rhaii/vllm-spyre-rhel9:1789681201 Red Hat AI Inference Server 3.4 2026-09-21T00:00:00Z RHSA-2026:69466 rhaii/vllm-cpu-rhel9:1789681128 Red Hat AI Inference Server 3.4 2026-09-21T00:00:00Z RHSA-2026:69467 rhaii/vllm-cuda-rhel9:1789681126 Red Hat AI Inference Server 3.4 2026-09-21T00:00:00Z RHSA-2026:69469 rhaii/vllm-rocm-rhel9:1789681126 Red Hat AI Inference Server Will not fix rhaiis/vllm-neuron-rhel9 Red Hat AI Inference Server Will not fix rhaiis/vllm-tpu-rhel9 Red Hat AI Inference Server Will not fix rhaii/vllm-gaudi-rhel9 Red Hat AI Inference Server Will not fix rhaii/vllm-neuron-rhel9 Red Hat AI Inference Server Will not fix rhaii/vllm-tpu-rhel9 Red Hat Enterprise Linux AI (RHEL AI) 3 Affected rhelai3/bootc-aws-cuda-rhel9 Red Hat Enterprise Linux AI (RHEL AI) 3 Affected rhelai3/bootc-azure-cuda-rhel9 Red Hat Enterprise Linux AI (RHEL AI) 3 Affected rhelai3/bootc-azure-rocm-rhel9 Red Hat Enterprise Linux AI (RHEL AI) 3 Affected rhelai3/bootc-cuda-rhel9 Red Hat Enterprise Linux AI (RHEL AI) 3 Affected rhelai3/bootc-gaudi-rhel9 Red Hat Enterprise Linux AI (RHEL AI) 3 Affected rhelai3/bootc-gcp-cuda-rhel9 Red Hat Enterprise Linux AI (RHEL AI) 3 Affected rhelai3/bootc-rocm-rhel9 Red Hat OpenShift AI (RHOAI) Not affected rhoai/odh-kserve-agent-rhel9 Red Hat OpenShift AI (RHOAI) Not affected rhoai/odh-kserve-controller-rhel9 Red Hat OpenShift AI (RHOAI) Not affected rhoai/odh-kserve-router-rhel9 Red Hat OpenShift AI (RHOAI) Not affected rhoai/odh-kserve-storage-initializer-rhel9 Red Hat OpenShift AI (RHOAI) Not affected rhoai/odh-llm-d-kv-cache-rhel9 Red Hat OpenShift AI (RHOAI) Affected rhoai/odh-vllm-gaudi-rhel9 https://www.cve.org/CVERecord?id=CVE-2026-55574 https://nvd.nist.gov/vuln/detail/CVE-2026-55574 https://github.com/vllm-project/vllm/commit/2b3006076c5e9bc4cda9e03e3641388de3c5c286 https://github.com/vllm-project/vllm/pull/45118 https://github.com/vllm-project/vllm/security/advisories/GHSA-rwxx-mrjm-wc2m