vLLM vulnerable to DoS via large Chat Completion or Tokenization requests with specially crafted `chat_template_kwargs`

{
  "id": "462a3de64014e2b8f5bbc525ca200b3549a0a17c317771de53eb7c86fb3156c8",
  "url": "https://osv.dev/vulnerability/CVE-2025-62426",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "vLLM vulnerable to DoS via large Chat Completion or Tokenization requests with specially crafted `chat_template_kwargs`",
    "summary": "vLLM is an inference and serving engine for large language models (LLMs). From version 0.5.5 to before 0.11.1, the /v1/chat/completions and /tokenize endpoints allow a chat_template_kwargs request parameter that is used in the code before it is properly validated against the chat template. With the right chat_template_kwargs parameters, it is possible to block processing of the API server for long periods of time, delaying all other requests. This issue has been patched in version 0.11.1.",
    "evidence": "osv:CVE-2025-62426",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2025-62426",
      "aliases": [
        "CVE-2025-62426",
        "GHSA-69j4-grxj-j64p",
        "PYSEC-2026-2012"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/vllm-project/vllm",
              "type": "GIT",
              "events": [
                {
                  "introduced": "09c7792610ada9f88bbf87d32b472dd44bf23cc2"
                },
                {
                  "fixed": "439368496db48d8f992ba8c606a0c0b1eebbfa69"
                },
                {
                  "introduced": "b761df963c2032144468a99bcb39a11e73e16ca4"
                },
                {
                  "fixed": "3ada34f9cb4d1af763fdfa3b481862a93eb6bd2b"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:vllm:vllm:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0.5.5"
                      },
                      {
                        "fixed": "0.11.1"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:vllm:vllm:0.11.1:rc0:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0.11.1-rc0"
                      },
                      {
                        "last_affected": "0.11.1-rc0"
                      }
                    ],
                    "source": "CPE_STRING"
                  },
                  {
                    "cpe": "cpe:2.3:a:vllm:vllm:0.11.1:rc1:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0.11.1-rc1"
                      },
                      {
                        "last_affected": "0.11.1-rc1"
                      }
                    ],
                    "source": "CPE_STRING"
                  },
                  {
                    "range": [
                      {
                        "fixed": "3ada34f9cb4d1af763fdfa3b481862a93eb6bd2b"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "0.11.1-rc0",
            "0.11.1-rc1",
            "v0.11.1rc1",
            "v0.11.1rc0",
            "v0.11.0rc1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-62426.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:40.139382315Z",
      "provider": "osv",
      "references": [
        "https://github.com/vllm-project/vllm/blob/2a6dc67eb520ddb9c4138d8b35ed6fe6226997fb/vllm/entrypoints/chat_utils.py#L1602-L1610",
        "https://github.com/vllm-project/vllm/blob/2a6dc67eb520ddb9c4138d8b35ed6fe6226997fb/vllm/entrypoints/openai/serving_engine.py#L809-L814",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/62xxx/CVE-2025-62426.json",
        "https://github.com/vllm-project/vllm/security/advisories/GHSA-69j4-grxj-j64p",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-62426",
        "https://github.com/vllm-project/vllm/commit/3ada34f9cb4d1af763fdfa3b481862a93eb6bd2b",
        "https://github.com/vllm-project/vllm/pull/27205"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-770"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/62xxx/CVE-2025-62426.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-62426",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 507766,
  "published_at": "2025-11-21T01:21:29.546+00:00"
}