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74 lines
2.7 KiB
Text
74 lines
2.7 KiB
Text
---
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title: security
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sidebarTitle: security
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---
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# `fastmcp.resources.security`
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Path-safety policy for templated resource parameters.
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Templated resources (`@mcp.resource("file:///{path}")`-style) extract
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parameter values straight out of the request URI and hand them to the
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resource function. When those values flow into filesystem or URI
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construction, a malicious client can smuggle path-traversal payloads
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(`../`, absolute paths, null bytes) through the template.
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`ResourceSecurity` screens extracted parameter values *before* the
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resource handler runs. It is applied by default to every templated
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read, mirroring the posture of the underlying MCP SDK's
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`ResourceSecurity` (traversal, absolute paths, and null bytes rejected).
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The screening reuses the SDK's component-based traversal check, so a
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value that merely *contains* dots (e.g. `HEAD~3..HEAD`, `v1..v2`,
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`file.tar.gz`) is not rejected — only an actual `..` path segment is.
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## Classes
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### `InheritSecurity` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/security.py#L49" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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Sentinel type: inherit the server-wide resource-security default.
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Distinguishes "no per-component policy was set" (inherit whatever the
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server configured) from an explicit ``None`` (screening disabled for
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this component).
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### `ResourceSecurity` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/security.py#L76" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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Security policy applied to extracted resource template parameters.
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These checks run after a URI has matched a template and its
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parameter values have been extracted and percent-decoded. They catch
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path-traversal and absolute-path injection regardless of how the
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value was encoded in the URI (literal, `%2F`, `%5C`, `%2E%2E`).
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All checks default on. Screen a value like `HEAD~3..HEAD` (dots
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inside a single segment) passes — only a standalone `..` segment is
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treated as traversal.
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**Methods:**
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#### `validate` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/security.py#L127" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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```python
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validate(self, params: Mapping[str, object]) -> str | None
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```
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Check all parameter values against the configured policy.
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String values (and lists of strings, from wildcard `{path*}`
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parameters that span multiple segments) are screened; non-string
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values are ignored, since traversal is a string-path concern.
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**Args:**
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- `params`: Extracted template parameters.
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**Returns:**
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- The name of the first parameter that fails, or `None` if all
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- values pass.
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