PT-2025-19362 · Pypi · Vllm

Published 2025-04-15 · Updated 2025-04-15

OSV

CVSS v3.1

6.5

Medium

Base vector

AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Impact

This report is to highlight a vulnerability in XGrammar, a library used by the structured output feature in vLLM. The XGrammar advisory is here: https://github.com/mlc-ai/xgrammar/security/advisories/GHSA-389x-67px-mjg3

The xgrammar library is the default backend used by vLLM to support structured output (a.k.a. guided decoding). Xgrammar provides a required, built-in cache for its compiled grammars stored in RAM. xgrammar is available by default through the OpenAI compatible API server with both the V0 and V1 engines.

A malicious user can send a stream of very short decoding requests with unique schemas, resulting in an addition to the cache for each request. This can result in a Denial of Service by consuming all of the system's RAM.

Note that even if vLLM was configured to use a different backend by default, it is still possible to choose xgrammar on a per-request basis using the guided decoding backend key of the extra body field of the request with the V0 engine. This per-request choice is not available when using the V1 engine.

Patches

• https://github.com/vllm-project/vllm/pull/16283

Workarounds

There is no way to workaround this issue in existing versions of vLLM other than preventing untrusted access to the OpenAI compatible API server.

References

• https://github.com/mlc-ai/xgrammar/security/advisories/GHSA-389x-67px-mjg3

Fix

Allocation of Resources Without Limits

Weakness Enumeration

CWE-770

CWE-1395

Related Identifiers

GHSA-HF3C-WXG2-49Q9

Affected Products

Vllm

References · 6

• https://osv.dev/vulnerability/GHSA-hf3c-wxg2-49q9 · Vendor Advisory
• https://github.com/vllm-project/vllm · Note
• https://github.com/vllm-project/vllm/pull/16283 · Note
• https://github.com/vllm-project/vllm/security/advisories/GHSA-hf3c-wxg2-49q9 · Note
• https://github.com/vllm-project/vllm/commit/cb84e45ac75b42ba6795145923e8eb323bb825ad · Note
• https://github.com/mlc-ai/xgrammar/security/advisories/GHSA-389x-67px-mjg3 · Note