CVE-2026-73556 vllm-project CVE debrief

Who should care

Defenders responsible for vLLM deployments should assess exposure to this vulnerability and prioritize upgrading to version 0.26.0 or later. They should also verify the affected scope, severity, and vendor guidance, and plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.

Why it matters

Defenders should prioritize verifying exposure to this vulnerability and upgrading to version 0.26.0 or later to prevent potential CPU core consumption and engine stall via catastrophic regular expression.

• Potential CPU core consumption and engine stall via catastrophic regular expression
• Verification of exposure and remediation priority

Technical summary

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, allowing an unauthenticated /v1/completions request to consume a CPU core and stall the structured-output engine path. This issue is fixed in version 0.26.0. The vulnerability allows an unauthenticated request to cause a denial-of-service (DoS) attack on the affected system, which could lead to a consumption of a CPU core and stall the structured-output engine path.

Defensive priority

Defenders should prioritize verifying exposure to this vulnerability and upgrading to version 0.26.0 or later.

Recommended defensive actions

• Verify exposure to this vulnerability in vLLM deployments
• Upgrade to version 0.26.0 or later
• Monitor for unauthenticated /v1/completions requests
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, but the scope of affected versions and deployments requires further verification. 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, allowing an unauthenticated /v1/completions request to consume a CPU core and stall the structured-output engine path. Defenders should verify exposure to this vulnerability and prioritize upgrading to

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.