Bug 2515404 (CVE-2026-73556)

Summary:	CVE-2026-73556 vllm: vLLM: Denial of Service via Regular Expression processing
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	alinfoot, bbrownin, dtrifiro, rbryant, weaton
Target Milestone:	---	Keywords:	Security
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Hardware:	All
OS:	Linux
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Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in vLLM, an inference and serving engine for large language models. An unauthenticated remote attacker can exploit a Regular Expression Denial of Service (ReDoS) vulnerability in the lm-format-enforcer backend. By submitting a specially crafted regular expression through the structured_outputs.regex parameter, the attacker can cause the system to consume excessive CPU resources. This leads to a denial of service, stalling the structured-output engine and preventing legitimate requests from being processed.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-08-13 15:51:37 UTC

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.