CVE-2026-73556

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

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

vllm-project · vllm

CVSS v3.1 GITHUB

5.3 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS

0.52% chance of exploitation in the next 30 days, 43rd percentile

Published

2026-08-13

Updated

2026-08-14

Proof-of-concept exploits (1)

• advisories/GHSA-48jh-3gj7-fg8v

Security advisories

• vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v
• vllm-project/vllm/pull/47595

References

• CVE Record
• NVD entry