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Critical

Token Cache Reuse in mcp-toolbox-sdk-python

Type: advisorySources: OSV

A caching flaw in the toolbox-core package of the mcp-toolbox-sdk-python SDK causes the same Google ID token to be cached and reused across different audiences. If an application uses the SDK to authenticate to two or more different audiences within the same process, the module-level token cache fails to key its cached tokens by the requested audience. Consequently, a valid, unexpired token minted for a sensitive service (Service A) can be retrieved from the cache and sent to a secondary service (Service B). An attacker who operates, compromises, or monitors traffic to Service B can capture this token and replay it to impersonate the victim application against Service A.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-19202
Confirmed fixed CVEs
Not specified
Updated in this feed
4 Nov 2026, 18:28 UTC · Revision 1

Source evidence

Token Cache Reuse in mcp-toolbox-sdk-python

core-osv · Original source

Published 22 Sept 2026, 21:48 UTC

A caching flaw in the toolbox-core package of the mcp-toolbox-sdk-python SDK causes the same Google ID token to be cached and reused across different audiences. If an application uses the SDK to authenticate to two or more different audiences within the same process, the module-level token cache fails to key its cached tokens by the requested audience. Consequently, a valid, unexpired token minted for a sensitive service (Service A) can be retrieved from the cache and sent to a secondary service (Service B). An attacker who operates, compromises, or monitors traffic to Service B can capture this token and replay it to impersonate the victim application against Service A.

osv:CVE-2026-19202
Complete source record
{
  "id": "c87d4cc0e609dd7c8b96650b26394a6945b205b7acc2193276b8305368eef496",
  "url": "https://osv.dev/vulnerability/CVE-2026-19202",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Token Cache Reuse in mcp-toolbox-sdk-python",
    "summary": "A caching flaw in the toolbox-core package of the mcp-toolbox-sdk-python SDK causes the same Google ID token to be cached and reused across different audiences. If an application uses the SDK to authenticate to two or more different audiences within the same process, the module-level token cache fails to key its cached tokens by the requested audience. Consequently, a valid, unexpired token minted for a sensitive service (Service A) can be retrieved from the cache and sent to a secondary service (Service B). An attacker who operates, compromises, or monitors traffic to Service B can capture this token and replay it to impersonate the victim application against Service A.",
    "evidence": "osv:CVE-2026-19202",
    "products": [],
    "severity": "critical",
    "structured": {
      "id": "CVE-2026-19202",
      "aliases": [
        "CVE-2026-19202"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/googleapis/mcp-toolbox-sdk-python",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "last_affected": "aa299d3bc8524ec0b99770adee880ed32a1bf818"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "last_affected": "1.1.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  }
                ]
              }
            }
          ],
          "versions": [
            "toolbox-core-v1.1.0",
            "release-please-611",
            "toolbox-llamaindex-v1.0.0",
            "release-please-589",
            "toolbox-langchain-v1.0.0",
            "release-please-591",
            "toolbox-adk-v1.0.0",
            "release-please-588",
            "toolbox-core-v1.0.0",
            "release-please-590",
            "toolbox-llamaindex-v0.6.0",
            "release-please-576",
            "toolbox-langchain-v0.6.0",
            "release-please-577",
            "toolbox-adk-v0.7.0",
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            "toolbox-core-v0.6.0",
            "release-please-574",
            "toolbox-llamaindex-v0.5.10",
            "release-please-557",
            "toolbox-langchain-v0.5.10",
            "release-please-558",
            "toolbox-adk-v0.6.1",
            "release-please-564",
            "toolbox-core-v0.5.10",
            "release-please-559",
            "toolbox-llamaindex-v0.5.9",
            "release-please-528",
            "toolbox-langchain-v0.5.9",
            "release-please-529",
            "toolbox-adk-v0.6.0",
            "release-please-526",
            "toolbox-core-v0.5.9",
            "release-please-527",
            "toolbox-adk-v0.5.8",
            "release-please-516",
            "toolbox-llamaindex-v0.5.8",
            "release-please-518",
            "toolbox-langchain-v0.5.8",
            "release-please-519",
            "toolbox-core-v0.5.8",
            "release-please-517",
            "toolbox-llamaindex-v0.5.7",
            "toolbox-langchain-v0.5.7",
            "toolbox-core-v0.5.7",
            "toolbox-adk-v0.5.7",
            "release-please-493",
            "toolbox-llamaindex-v0.5.6",
            "toolbox-langchain-v0.5.6",
            "toolbox-core-v0.5.6",
            "toolbox-adk-v0.5.6",
            "release-please-491",
            "toolbox-llamaindex-v0.5.4",
            "toolbox-langchain-v0.5.4",
            "toolbox-core-v0.5.4",
            "release-please-432",
            "toolbox-llamaindex-v0.5.3",
            "toolbox-langchain-v0.5.3",
            "toolbox-core-v0.5.3",
            "release-please-381",
            "toolbox-llamaindex-v0.5.2",
            "toolbox-langchain-v0.5.2",
            "toolbox-core-v0.5.2",
            "release-please-373",
            "toolbox-llamaindex-v0.5.1",
            "toolbox-langchain-v0.5.1",
            "toolbox-core-v0.5.1",
            "release-please-343",
            "toolbox-llamaindex-v0.5.0",
            "toolbox-langchain-v0.5.0",
            "toolbox-core-v0.5.0",
            "release-please-317",
            "toolbox-llamaindex-v0.4.0",
            "toolbox-langchain-v0.4.0",
            "toolbox-core-v0.4.0",
            "release-please-304",
            "toolbox-llamaindex-v0.3.0",
            "toolbox-langchain-v0.3.0",
            "toolbox-core-v0.3.0",
            "release-please-285",
            "toolbox-llamaindex-v0.2.1",
            "toolbox-langchain-v0.2.1",
            "toolbox-core-v0.2.1",
            "release-please-262",
            "toolbox-llamaindex-v0.2.0",
            "toolbox-langchain-v0.2.0",
            "toolbox-core-v0.2.0",
            "toolbox-core-v0.1.0",
            "toolbox-langchain-v0.1.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-19202.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:38.387305188Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/19xxx/CVE-2026-19202.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-19202",
        "https://github.com/googleapis/mcp-toolbox-sdk-python/pull/675"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-524"
        ],
        "cna_assigner": "Google",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/19xxx/CVE-2026-19202.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-19202",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 505694,
  "published_at": "2026-09-22T21:48:26.539+00:00"
}