---
id: CVE-2026-115911
aliases:
  - GHSA-542m-9234-8gvf
  - PYSEC-2026-4344
title: >-
  vLLM: DoS via unbounded chat_template Jinja2 rendering exhausts the renderer
  thread pool
summary: >-
  vLLM: DoS via unbounded chat_template Jinja2 rendering exhausts the renderer
  thread pool
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
vendor: vllm
product: vllm
ecosystem: pip
affected:
  - 'vllm >= 0.19.0, < 0.32.0'
patched:
  - vllm 0.32.0
published: '2026-10-28'
updated: '2026-10-29'
sourceUpdated: '2026-10-29T11:10:38.035035010Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-542m-9234-8gvf'
references:
  - url: >-
      https://github.com/vllm-project/vllm/security/advisories/GHSA-542m-9234-8gvf
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-115911'
  - url: 'https://github.com/vllm-project/vllm/pull/50300'
  - url: >-
      https://github.com/vllm-project/vllm/commit/cff08b461e086523cee8bba5bd3c66d302625134
  - url: 'https://github.com/vllm-project/vllm'
  - url: 'https://github.com/vllm-project/vllm/releases/tag/v0.32.0'
  - url: 'https://github.com/advisories/GHSA-542m-9234-8gvf'
tags:
  - osv
  - pip
  - ghsa
  - cve.org
epss: 0.00312
epssPercentile: 0.24041
cwe:
  - CWE-400
  - CWE-770
  - CWE-834
ingestedAt: '2026-10-26T17:33:33.065Z'
---

## Overview

### Summary
vLLM renders chat templates by passing the resolved Jinja2 source to `tokenizer.apply_chat_template()`, which compiles and `.render()`s it in an `ImmutableSandboxedEnvironment`. The sandbox prevents code-execution escapes but imposes **no wall-clock timeout, no output-size cap, and no nested-loop or binop limit**. The render runs in a `ThreadPoolExecutor` whose `max_workers` defaults to **1**, and CPython worker threads cannot be interrupted. An authenticated API client (or a malicious model repo loaded with `trust_remote_code=False`) can therefore submit a single short template and permanently wedge **all** chat-style endpoints (`/v1/chat/completions`, `/v1/responses`, `/tokenize`, `/pooling`-chat, `/invocations`-chat) for every tenant until the process is restarted. A string-multiplication variant instead OOM-kills the API-server process. Because of a separately-reported (GHSA-jmjw-q4x3-hmc2) gate omission on `/v1/responses`, the remote authenticated attacker vector works in **default `vllm serve` configuration** with no operator opt-in.

### Impact
A single authenticated request of <100 bytes permanently denies all chat-style inference (`/v1/chat/completions`, `/v1/responses`, `/tokenize`, `/pooling`-chat, `/invocations`-chat) to **every tenant** of the API-server replica until the operator restarts the process. The string-multiplication variant OOM-kills the process. In a multi-tenant deployment this is a cross-tenant denial-of-service from any one tenant. From the malicious-model angle, a model repo whose `tokenizer_config.json` carries the hostile template wedges every replica that loads it on the first legitimate chat request, with `trust_remote_code=False`.

**Preconditions:** any non-harmony model (`model_type != gpt_oss`); `renderer_num_workers` at its default of 1; for the default-config authenticated API attacker vector, `--chat-template` must be unset (the default because most HF models ship their own).
**Blast radius:** API-server process, per replica. Engine/worker processes unaffected by the CPU variant (event loop survives); affected by the memory variant (process OOM).
**Persistence:** until process restart. Survives client disconnect.

This advisory was fixed in [MR50300](https://github.com/vllm-project/vllm/pull/50300).

## Affected packages

- `vllm >= 0.19.0, < 0.32.0`

## Remediation

Upgrade to a patched release:

- `vllm 0.32.0`