[Bug]: REST task/request id sanitization #805

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1. bartek-w

   added a parent issue on Mar 11, 2026

   • 1.0 Release #701
2. bartek-w

   added the

   Bug

   issue type on Mar 11, 2026
3. rohityan

   added

   maintainers-only

   on Mar 11, 2026
4. ishymko

   removed a parent issue on Apr 9, 2026

   • 1.0 Release #701
5. mtsmyassin commented on Apr 17, 2026

   

   mtsmyassin

   on Apr 17, 2026

   More actions

   Proposed Fix: Validate task/request IDs in REST transport

   The REST transport exposes endpoints like GET /v1/tasks/{task_id} where task_id comes directly from the URL path. Since these IDs are later used to look up tasks in the store (and potentially in file paths or database keys), accepting values like ../secret or ../../etc/passwd could be dangerous.

   Root Cause

   Starlette path parameters are URL-decoded by the time they reach the handler, so a request to /v1/tasks/..%2F..%2Fconfig would arrive as ../../config. Without sanitization this string is passed verbatim to task_store.get().

   Suggested Fix

   Add a shared validator function and apply it as a Starlette dependency (or inline check) at the REST handler layer:

   import re
   from a2a.types import InvalidParamsError
   from a2a.utils.errors import ServerError
   
   # Only allow characters that are safe in a task/request ID:
   # alphanumerics, hyphens, underscores, dots (but not leading dots)
   _SAFE_ID_RE = re.compile(r'^[a-zA-Z0-9][a-zA-Z0-9_\-\.]{0,127}$')
   
   def validate_task_id(task_id: str) -> str:
       """Validates that a task/request ID is safe to use."""
       if not task_id or not _SAFE_ID_RE.match(task_id):
           raise ServerError(
               error=InvalidParamsError(
                   message=f'Invalid task ID format: {task_id!r}'
               )
           )
       return task_id

   This can be called at the top of every REST handler that accepts a path parameter:

   async def get_task(request: Request) -> Response:
       task_id = validate_task_id(request.path_params["task_id"])
       # ...

   Alternative: Starlette Path Regex Constraint

   Starlette also supports regex constraints directly in route definitions, which catches the issue before it even reaches handler code:

   Route("/v1/tasks/{task_id:str}", endpoint=get_task)
   # becomes:
   Route(r"/v1/tasks/{task_id:[a-zA-Z0-9][a-zA-Z0-9_\-\.]{0,127}}", endpoint=get_task)

   However, this only works if path parameters are defined with regex syntax, which requires Starlette ≥ 0.20. The inline validate_task_id() approach is more portable and gives a better error message to clients.

   Notes

   • The same validation should apply to context_id if it appears as a path parameter.
   • • JSON-RPC transport is not affected because IDs come in the request body and Pydantic already validates them as strings; the attack surface is the URL path.
   • • • The InvalidParamsError response ensures spec-compliant error responses (-32602).
         Happy to submit a PR for this if it would be helpful.
6. Linux2010

   added a commit that references this issue on Jul 26, 2026

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7. Linux2010

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8. Linux2010

   added a commit that references this issue on Aug 14, 2026

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9. Linux2010

   added a commit that references this issue on Sep 16, 2026

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