vllm-project vLLM up to 0.23.x xgrammar Backend/outlines Backend structured_outputs.regex incorrect regex

Summaryinfo

A vulnerability marked as problematic has been reported in vllm-project vLLM up to 0.23.x. This affects an unknown function of the file structured_outputs.regex of the component xgrammar Backend/outlines Backend. Performing a manipulation results in incorrect regex. This vulnerability is reported as CVE-2026-55574. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability, which was classified as problematic, was found in vllm-project vLLM up to 0.23.x. This affects an unknown code of the file structured_outputs.regex of the component xgrammar Backend/outlines Backend. The manipulation with an unknown input leads to a incorrect regex vulnerability. CWE is classifying the issue as CWE-185. The product specifies a regular expression in a way that causes data to be improperly matched or compared. This is going to have an impact on availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-55574 since 06/17/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 0.24.0 eliminates this vulnerability.

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Productinfo

Type

• Project Management Software

Vendor

• vllm-project

Name

• vLLM

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6
• 0.7
• 0.8
• 0.9
• 0.10
• 0.11
• 0.12
• 0.13
• 0.14
• 0.15
• 0.16
• 0.17
• 0.18
• 0.19
• 0.20
• 0.21
• 0.22
• 0.23

Website

• Product: https://github.com/vllm-project/vllm/

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