vllm-project vLLM up to 0.25.x lm-format-enforcer backend backend_lm_format_enforcer.py structured_outputs.regex incorrect regex

Summaryinfo

A vulnerability classified as problematic has been found in vllm-project vLLM up to 0.25.x. Impacted is the function validate_structured_output_request_lm_format_enforcer of the file vllm/v1/structured_output/backend_lm_format_enforcer.py of the component lm-format-enforcer backend. This manipulation of the argument structured_outputs.regex causes incorrect regex. This vulnerability is tracked as CVE-2026-73556. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability classified as problematic was found in vllm-project vLLM up to 0.25.x. Affected by this vulnerability is the function validate_structured_output_request_lm_format_enforcer of the file vllm/v1/structured_output/backend_lm_format_enforcer.py of the component lm-format-enforcer backend. The manipulation of the argument structured_outputs.regex with an unknown input leads to a incorrect regex vulnerability. The CWE definition for the vulnerability is CWE-185. The product specifies a regular expression in a way that causes data to be improperly matched or compared. As an impact it is known to affect availability. The summary by CVE is:

vLLM is an inference and serving engine for large language models. Prior to 0.26.0, the structured_outputs.regex parameter in vllm/v1/structured_output/backend_lm_format_enforcer.py is passed to lmformatenforcer.RegexParser without compile_regex_with_timeout or validation in validate_structured_output_request_lm_format_enforcer, allowing an unauthenticated /v1/completions request against the lm-format-enforcer backend to consume a CPU core and stall the structured-output engine path with a catastrophic regular expression. This issue is fixed in version 0.26.0.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-73556 since 08/12/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 0.26.0 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
• 0.24
• 0.25

Website

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

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