What’s Vulnerable › Vulnerabilities

CVE-2026-55574: vLLM: ReDoS via structured_outputs.regex compiled without timeout in xgrammar and outlines backends

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-06 · updated 2026-10-25
• Weakness: CWE-1333

Description

vLLM is a high-throughput and memory-efficient inference and serving engine for LLMs. Prior to 0.24.0, the structured_outputs.regex API parameter passes a user-supplied regular expression string directly to the grammar compiler backends with no compilation timeout; in the xgrammar backend the string reaches the regex compiler with no guard, and in the outlines backend the validation step blocks structural issues such as lookarounds and backreferences but performs no complexity analysis, so a pattern with nested quantifiers passes all checks and causes exponential state-space expansion, allowing a single request containing an adversarial regex to hang an inference worker indefinitely and deny service. This issue is fixed in version 0.24.0.

Affected products

• vllm-project vllm: before 0.24.0 — fixed in 0.24.0

How to fix

Upgrade to a fixed version: vllm-project vllm 0.24.0. Check the vendor advisory for mitigations.

References

• https://github.com/vllm-project/vllm/commit/2b3006076c5e9bc4cda9e03e3641388de3c5c286
• https://github.com/vllm-project/vllm/pull/45118
• https://github.com/vllm-project/vllm/security/advisories/GHSA-rwxx-mrjm-wc2m

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