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CVE-2026-73556— vLLM: ReDoS via structured_outputs.regex in the lm-format-enforcer backend (no compile timeout) — missed sibling of CVE-2026-55574

Quick assessment

Affected
vllm-project vllm
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

vLLM是vLLM团队开源的一个适用于 LLM 的高吞吐量和内存高效推理和服务引擎。 vLLM 0.26.0之前版本存在资源管理错误漏洞，该漏洞源于structured_outputs.regex参数传递给lmformatenforcer.RegexParser时未进行编译正则表达式超时或验证，可能导致未经身份验证的/v1/completions请求消耗CPU核心并停滞结构化输出引擎路径，造成拒绝服务。

CVSS 5.3 · Medium EPSS 0.52% · P42

Affected Version Matrix 1

VendorProduct Version RangeStatus
vllm-project vllm < 0.26.0 affected
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I. Basic Information for CVE-2026-73556

Vulnerability Information
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Vulnerability Title
vLLM: ReDoS via structured_outputs.regex in the lm-format-enforcer backend (no compile timeout) — missed sibling of CVE-2026-55574
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5
Vulnerability Title
vLLM 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
vLLM是vLLM团队开源的一个适用于 LLM 的高吞吐量和内存高效推理和服务引擎。 vLLM 0.26.0之前版本存在资源管理错误漏洞，该漏洞源于structured_outputs.regex参数传递给lmformatenforcer.RegexParser时未进行编译正则表达式超时或验证，可能导致未经身份验证的/v1/completions请求消耗CPU核心并停滞结构化输出引擎路径，造成拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
vllm-project vllm < 0.26.0 -

II. Public POCs for CVE-2026-73556

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III. Intelligence Information for CVE-2026-73556

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Patches & Fixes for CVE-2026-73556 (2)

Vendor Advisories for CVE-2026-73556 (1)

Vendor Pages for CVE-2026-73556 (1)

Same Patch Batch · vllm-project · 2026-08-13 · 5 CVEs total

CVE-2026-73559 6.5 MEDIUM vLLM: Completion prompt lists fan out into unbounded engine requests
CVE-2026-73557 6.3 MEDIUM vLLM: Incomplete CVE-2025-62164 remediation can be bypassed by concurrent prompt parts
CVE-2026-73555 5.3 MEDIUM vLLM: Unauthenticated Internal Path and Username Disclosure via Validation Error Messages
CVE-2026-73558 5.3 MEDIUM vLLM: Cross-User Data Leak Vulnerability

IV. Related Vulnerabilities

Same product: vllm
Same vendor: vllm-project
Same weakness: CWE-400

V. Comments for CVE-2026-73556

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