What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-13 · updated 2026-09-28
• Weakness: CWE-400

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.

Affected products

• vllm-project vllm: before 0.26.0 — fixed in 0.26.0

How to fix

Upgrade to a fixed version: vllm-project vllm 0.26.0. Check the vendor advisory for mitigations.

References

• https://github.com/vllm-project/vllm/commit/c9a788eedc412acceaa5112e0d44624b49841577
• https://github.com/vllm-project/vllm/pull/47595
• https://github.com/vllm-project/vllm/releases/tag/v0.26.0
• https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v
• https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v

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