Google mcp-toolbox-sdk-python up to 1.1.0 toolbox-core authentication replay

Summaryinfo

A vulnerability was found in Google mcp-toolbox-sdk-python up to 1.1.0. It has been declared as critical. This issue affects some unknown processing of the component toolbox-core. Such manipulation leads to authentication replay. This vulnerability is traded as CVE-2026-19202. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Google mcp-toolbox-sdk-python up to 1.1.0. Affected by this issue is some unknown processing of the component toolbox-core. The manipulation with an unknown input leads to a authentication replay vulnerability. Using CWE to declare the problem leads to CWE-294. A capture-replay flaw exists when the design of the product makes it possible for a malicious user to sniff network traffic and bypass authentication by replaying it to the server in question to the same effect as the original message (or with minor changes). Impacted is confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-19202 since 08/07/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $5k-$25k (estimation calculated on 09/23/2026). The MITRE ATT&CK project declares the attack technique as T1040.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• Programming Language Software

Vendor

• Google

Name

• mcp-toolbox-sdk-python

Version

• 1.0
• 1.1.0

License

• free

Website

• Vendor: https://www.google.com/

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