High [CVE-2026-73556] Denial of Service via Regular Expression processing
This high-severity Red Hat Linux advisory covers CVE-2026-73556 affecting Red Hat AI Inference Server, Red Hat Enterprise Linux AI (RHEL AI) 3, Red Hat OpenShift AI (RHOAI).
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Summary
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.
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. Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
Weakness: CWE-1333. Affected Red Hat products: Red Hat AI Inference Server; Red Hat Enterprise Linux AI (RHEL AI) 3; Red Hat OpenShift AI (RHOAI).
Red Hat does not currently list a fixing RHSA for this CVE.
- < 0.26.0
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
Mitigation
Upgrade to a fixed release: 0.26.0. That is the remediation for this advisory.
The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
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