CVE-2026-55574

Description

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.

How to fix CVE-2026-55574

To remediate CVE-2026-55574, upgrade the affected package to a fixed version below.

• —upgrade to 0.24.0 or later

Is CVE-2026-55574 being exploited?

Low — EPSS is 0.3%, meaning exploitation activity has not been observed at scale.

Affected packages (1)

• from 0, < 0.24.0

CVSS scores

References (6)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-55574
• PATCHgithub.com/vllm-project/vllm
• WEBgithub.com/pypa/advisory-database/tree/main/vulns/vllm/PYSEC-2026-2304.yaml
• WEBgithub.com/vllm-project/vllm/commit/2b3006076c5e9bc4cda9e03e3641388de3c5c286