diff --git a/src/scriptworker/context.py b/src/scriptworker/context.py
index f60059e5..a57eb0f3 100644
--- a/src/scriptworker/context.py
+++ b/src/scriptworker/context.py
@@ -59,6 +59,7 @@ class Context(object):
 
     config: Optional[Dict[str, Any]] = None
     credentials_timestamp: Optional[int] = None
+    credentials_fd: int = -1
     proc: Optional[task_process.TaskProcess] = None
     queue: Optional[Queue] = None
     session: Optional[aiohttp.ClientSession] = None
@@ -98,6 +99,8 @@ def claim_task(self, claim_task: Optional[Dict[str, Any]]) -> None:
         if claim_task:
             self.task = claim_task["task"]
             self.verify_task()
+            # flags=0 to let the child inherit this fd
+            self.credentials_fd = os.memfd_create("scriptworker_temp_creds", flags=0)
             self.temp_credentials = claim_task["credentials"]
             path = os.path.join(self.config["work_dir"], "task.json")
             assert self.task
@@ -105,6 +108,8 @@ def claim_task(self, claim_task: Optional[Dict[str, Any]]) -> None:
         else:
             self.temp_credentials = None
             self.task = None
+            os.close(self.credentials_fd)
+            self.credentials_fd = -1
 
     def verify_task(self) -> None:
         """Run some task sanity checks on ``self.task``."""
@@ -193,6 +198,10 @@ def temp_credentials(self) -> Optional[Dict[str, Any]]:
     def temp_credentials(self, credentials: Optional[Dict[str, Any]]) -> None:
         self._temp_credentials = credentials
         self.temp_queue = self.create_queue(self.temp_credentials)
+        if credentials:
+            data = json.dumps(credentials, indent=2, sort_keys=True).encode("ascii")
+            # use pwrite so we don't confuse the child by changing the file offset
+            assert os.pwrite(self.credentials_fd, data, 0) == len(data)
 
     def write_json(self, path: str, contents: Dict[str, Any], message: str) -> None:
         """Write json to disk.
diff --git a/src/scriptworker/task.py b/src/scriptworker/task.py
index 4f4751ab..ad0e8d69 100644
--- a/src/scriptworker/task.py
+++ b/src/scriptworker/task.py
@@ -672,7 +672,16 @@ async def run_task(context, to_cancellable_process):
     env["TASK_ID"] = context.task_id or "None"
     env["RUN_ID"] = str(get_run_id(context.claim_task))
     env["TASKCLUSTER_ROOT_URL"] = context.config["taskcluster_root_url"]
-    kwargs = {"stdout": PIPE, "stderr": PIPE, "stdin": None, "close_fds": True, "preexec_fn": lambda: os.setsid(), "env": env}  # pragma: no branch
+    env["TASKCLUSTER_CREDENTIALS_FD"] = str(context.credentials_fd)
+    kwargs = {
+        "stdout": PIPE,
+        "stderr": PIPE,
+        "stdin": None,
+        "close_fds": True,
+        "preexec_fn": lambda: os.setsid(),
+        "env": env,
+        "pass_fds": (context.credentials_fd,),
+    }  # pragma: no branch
 
     timeout = get_task_maxruntime(context.task, context.config["task_max_timeout"])
     subprocess = await asyncio.create_subprocess_exec(*context.config["task_script"], **kwargs)
diff --git a/tests/test_context.py b/tests/test_context.py
index ff534cf8..5549262c 100644
--- a/tests/test_context.py
+++ b/tests/test_context.py
@@ -77,6 +77,46 @@ async def test_set_reset_task(rw_context, claim_task, reclaim_task):
     assert rw_context.temp_queue is None
 
 
+def test_credentials_fd_initial(rw_context):
+    assert rw_context.credentials_fd == -1
+
+
+@pytest.mark.asyncio
+async def test_credentials_fd_opened_on_claim_task(rw_context, claim_task):
+    rw_context.claim_task = claim_task
+    assert rw_context.credentials_fd >= 0
+    os.fstat(rw_context.credentials_fd)  # raises OSError if fd is invalid
+
+
+@pytest.mark.asyncio
+async def test_credentials_fd_content(rw_context, claim_task):
+    rw_context.claim_task = claim_task
+    fd = rw_context.credentials_fd
+    size = os.fstat(fd).st_size
+    data = os.pread(fd, size, 0)
+    assert json.loads(data) == claim_task["credentials"]
+
+
+@pytest.mark.asyncio
+async def test_credentials_fd_updated_on_reclaim(rw_context, claim_task, reclaim_task):
+    rw_context.claim_task = claim_task
+    rw_context.reclaim_task = reclaim_task
+    fd = rw_context.credentials_fd
+    size = os.fstat(fd).st_size
+    data = os.pread(fd, size, 0)
+    assert json.loads(data) == reclaim_task["credentials"]
+
+
+@pytest.mark.asyncio
+async def test_credentials_fd_closed_on_reset(rw_context, claim_task):
+    rw_context.claim_task = claim_task
+    fd = rw_context.credentials_fd
+    rw_context.claim_task = None
+    assert rw_context.credentials_fd == -1
+    with pytest.raises(OSError):
+        os.fstat(fd)
+
+
 @pytest.mark.asyncio
 async def test_projects(rw_context, mocker):
     fake_projects = {"mozilla-central": "blah", "count": 0}
diff --git a/tests/test_task.py b/tests/test_task.py
index 1b38e324..121a521c 100644
--- a/tests/test_task.py
+++ b/tests/test_task.py
@@ -567,6 +567,24 @@ async def test_run_task_timeout(context):
     assert context.proc is None
 
 
+@pytest.mark.asyncio
+async def test_run_task_credentials_fd(context):
+    """The subprocess receives the temp credentials via the fd in TASKCLUSTER_CREDENTIALS_FD."""
+    context.config["task_script"] = (
+        sys.executable,
+        "-c",
+        "import json, os, sys; "
+        "fd = int(os.environ['TASKCLUSTER_CREDENTIALS_FD']); "
+        "size = os.fstat(fd).st_size; "
+        "sys.stdout.write(os.pread(fd, size, 0).decode('ascii'))",
+    )
+    await swtask.run_task(context, noop_to_cancellable_process)
+    log_file = log.get_log_filename(context)
+    contents = read(log_file)
+    parsed, _ = json.JSONDecoder().raw_decode(contents)
+    assert parsed == context.temp_credentials
+
+
 # report* {{{1
 @pytest.mark.asyncio
 async def test_reportCompleted(context, successful_queue):