Token Cache Reuse in mcp-toolbox-sdk-python

Answer in brief

CVE-2026-19202 records a Critical severity (CVSS 9.1) vulnerability in Token Cache Reuse in mcp-toolbox-sdk-python. The current sources do not mark it as known exploited. The current feed maps Google/mcp-toolbox-sdk-python (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 22, 2026Updated Sep 22, 2026Source checked Sep 22, 2026First seen by HOL Sep 22, 2026Material review Sep 22, 2026

Upstream Advisory

Key facts

Risk: Critical · CVSS 9.1
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

CVSS is 9.1. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Google/mcp-toolbox-sdk-python (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Google/mcp-toolbox-sdk-pythongeneric	>=0 <=1.1.0	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Google/mcp-toolbox-sdk-python.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Sep 22, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 22, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 22, 2026

Sources and claim methodology

GitHub security advisorygithub.com

Upstream source description

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.

Quoted source text, attributed separately from HOL analysis.