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

Published Aug 13, 2026
·
Updated

vLLM is an inference and serving engine for large language models. Prior to 0.26.0, the structuredoutputs.regex parameter in vllm/v1/structuredoutput/backendlmformatenforcer.py is passed to lmformatenforcer.RegexParser without compileregexwithtimeout or validation in validatestructuredoutputrequestlmformatenforcer, 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.

Affected Software

1 affected component
vllm vllm<0.26.0

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade vllm to a version that resolves this vulnerability.

    Fixed in 0.26.0

Event History

Aug 13, 2026
CVE Published
via MITRE·02:56 PM
Data Sourced
via MITRE·02:56 PM
DescriptionSeverityWeakness
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Frequently Asked Questions

1

What is the severity of CVE-2026-73556?

The severity of CVE-2026-73556 is classified as medium with a score of 5.3.

2

How do I fix CVE-2026-73556?

To fix CVE-2026-73556, upgrade the vLLM software to version 0.26.0 or later.

3

What is the nature of the vulnerability described in CVE-2026-73556?

CVE-2026-73556 is a ReDoS vulnerability in the vLLM structured_outputs.regex parameter due to a lack of compile timeout.

4

Which versions of vLLM are affected by CVE-2026-73556?

Versions of vLLM prior to 0.26.0 are affected by CVE-2026-73556.

5

What component is specifically involved in CVE-2026-73556?

The structured_outputs.regex parameter in the lm-format-enforcer backend is specifically involved in CVE-2026-73556.

Company

Resources

Contact

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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 - SecAlerts