CVE-2026-55574

vLLM: ReDoS via structured_outputs.regex compiled without timeout in xgrammar and outlines backends

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.

Scores

Weaknesses (CWE)

• CWE-1333

Advisories

• GHSA-rwxx-mrjm-wc2m — vLLM: ReDoS via structured_outputs.regex compiled without timeout in xgrammar and outlines backends
• PYSEC-2026-2304 — 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-

European references

• ENISA EUVD · EUVD-2026-41924
• GCVE · GCVE-0-2026-55574

Affected configurations (NVD CPE)

• cpe:2.3:a:vllm:vllm:*:*:*:*:*:*:*:* < 0.24.0

Affected products

References

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

Sources