diff --git a/common/misc_utils.py b/common/misc_utils.py
index 1826be77f3..9225fcd25d 100644
--- a/common/misc_utils.py
+++ b/common/misc_utils.py
@@ -24,22 +24,146 @@ import subprocess
 import sys
 import threading
 import uuid
+from urllib.parse import urljoin
 
 from concurrent.futures import ThreadPoolExecutor
 
+logger = logging.getLogger(__name__)
+
 
 def get_uuid():
     return uuid.uuid1().hex
 
 
+# OAuth avatar fetch: bounded size; each redirect hop is SSRF-checked and DNS-pinned
+# (see common.ssrf_guard).
+_OAUTH_AVATAR_MAX_BYTES = int(os.environ.get("RAGFLOW_OAUTH_AVATAR_MAX_BYTES", str(5 * 1024 * 1024)))
+_OAUTH_AVATAR_MAX_REDIRECTS = int(os.environ.get("RAGFLOW_OAUTH_AVATAR_MAX_REDIRECTS", "5"))
+_REDIRECT_STATUS = frozenset({301, 302, 303, 307, 308})
+
+
 async def download_img(url):
+    """Fetch an image URL and return a data URI, or empty string on failure / SSRF block.
+
+    URLs must resolve only to globally routable addresses; redirects are followed
+    only up to ``_OAUTH_AVATAR_MAX_REDIRECTS`` with each target validated.
+    """
     if not url:
         return ""
-    from common.http_client import async_request
-    response = await async_request("GET", url)
-    return "data:" + \
-        response.headers.get('Content-Type', 'image/jpg') + ";" + \
-        "base64," + base64.b64encode(response.content).decode("utf-8")
+    if not isinstance(url, str):
+        url = str(url)
+    url = url.strip()
+    if not url:
+        return ""
+
+    current_url = url
+    redirect_hops = 0
+
+    # Match common/http_client.py defaults without importing http_client (avoids
+    # pulling settings and keeps this path usable in lightweight test envs).
+    request_timeout = float(os.environ.get("HTTP_CLIENT_TIMEOUT", "15"))
+    proxy = os.environ.get("HTTP_CLIENT_PROXY")
+    user_agent = os.environ.get("HTTP_CLIENT_USER_AGENT", "ragflow-http-client")
+
+    from common.ssrf_guard import assert_url_is_safe, pin_dns_global
+
+    while redirect_hops <= _OAUTH_AVATAR_MAX_REDIRECTS:
+        try:
+            hostname, pin_ip = assert_url_is_safe(current_url)
+        except ValueError as exc:
+            logger.warning("download_img rejected URL (SSRF guard): %s", exc)
+            return ""
+
+        import httpx
+
+        timeout = httpx.Timeout(request_timeout)
+        headers = {}
+        if user_agent:
+            headers["User-Agent"] = user_agent
+
+        async def _stream_one_get() -> tuple[str, str | None]:
+            """Return ``('redirect', new_url)``, ``('data', data_uri)``, or ``('fail', None)``."""
+            with pin_dns_global(hostname, pin_ip):
+                async with httpx.AsyncClient(
+                    timeout=timeout,
+                    follow_redirects=False,
+                    proxy=proxy,
+                ) as client:
+                    async with client.stream("GET", current_url, headers=headers or None) as response:
+                        if response.status_code in _REDIRECT_STATUS:
+                            await response.aclose()
+                            location = response.headers.get("location")
+                            if not location:
+                                logger.warning(
+                                    "download_img redirect missing Location header: url=%r status=%s redirect_hops=%s",
+                                    current_url,
+                                    response.status_code,
+                                    redirect_hops,
+                                )
+                                return ("fail", None)
+                            return ("redirect", urljoin(current_url, location))
+                        if response.status_code != 200:
+                            logger.warning(
+                                "download_img non-200 response: url=%r status=%s redirect_hops=%s",
+                                current_url,
+                                response.status_code,
+                                redirect_hops,
+                            )
+                            return ("fail", None)
+                        body = bytearray()
+                        async for chunk in response.aiter_bytes():
+                            if len(body) + len(chunk) > _OAUTH_AVATAR_MAX_BYTES:
+                                logger.warning(
+                                    "download_img response exceeded max size: url=%r max_bytes=%s",
+                                    current_url,
+                                    _OAUTH_AVATAR_MAX_BYTES,
+                                )
+                                await response.aclose()
+                                return ("fail", None)
+                            body.extend(chunk)
+                        content_type = response.headers.get("Content-Type", "image/jpeg")
+                        data_uri = (
+                            "data:"
+                            + content_type
+                            + ";base64,"
+                            + base64.b64encode(bytes(body)).decode("utf-8")
+                        )
+                        return ("data", data_uri)
+
+        try:
+            kind, payload = await asyncio.wait_for(_stream_one_get(), timeout=request_timeout)
+        except asyncio.TimeoutError:
+            logger.warning(
+                "download_img total wall-clock timeout: url=%r redirect_hops=%s timeout=%s",
+                current_url,
+                redirect_hops,
+                request_timeout,
+            )
+            return ""
+        except Exception as exc:
+            logger.warning(
+                "download_img request failed: url=%r redirect_hops=%s err=%s",
+                current_url,
+                redirect_hops,
+                exc,
+            )
+            return ""
+
+        if kind == "redirect":
+            current_url = str(payload)
+            redirect_hops += 1
+            continue
+        if kind == "fail":
+            return ""
+        return str(payload)
+
+    logger.warning(
+        "download_img redirect hop limit exceeded: url=%r redirect_hops=%s max_redirects=%s",
+        current_url,
+        redirect_hops,
+        _OAUTH_AVATAR_MAX_REDIRECTS,
+    )
+    return ""
 
 
 def hash_str2int(line: str, mod: int = 10 ** 8) -> int:
diff --git a/test/unit_test/common/test_misc_utils.py b/test/unit_test/common/test_misc_utils.py
index 82c8f97657..6ca24f1bbd 100644
--- a/test/unit_test/common/test_misc_utils.py
+++ b/test/unit_test/common/test_misc_utils.py
@@ -13,10 +13,96 @@
 #  See the License for the specific language governing permissions and
 #  limitations under the License.
 #
-import uuid
+import asyncio
 import hashlib
-import pytest
-from common.misc_utils import get_uuid, download_img, hash_str2int, convert_bytes
+import sys
+import types
+import uuid
+from contextlib import contextmanager
+from unittest.mock import patch
+
+from common import ssrf_guard
+from common.misc_utils import convert_bytes, download_img, get_uuid, hash_str2int
+
+
+class _Hdr:
+    def __init__(self, mapping: dict[str, str]):
+        self._m = {k.lower(): v for k, v in mapping.items()}
+
+    def get(self, key: str, default=None):
+        return self._m.get(key.lower(), default)
+
+
+class _MockStreamResp:
+    def __init__(self, status_code: int, *, location: str | None = None, body: bytes = b""):
+        self.status_code = status_code
+        hdrs: dict[str, str] = {}
+        if location is not None:
+            hdrs["Location"] = location
+        if body:
+            hdrs.setdefault("Content-Type", "image/jpeg")
+        self.headers = _Hdr(hdrs)
+        self._body = body
+
+    async def aclose(self):
+        return None
+
+    async def aiter_bytes(self):
+        if self._body:
+            yield self._body
+
+
+class _FakeStreamCtx:
+    def __init__(self, resp: _MockStreamResp):
+        self._resp = resp
+
+    async def __aenter__(self):
+        return self._resp
+
+    async def __aexit__(self, exc_type, exc, tb):
+        return None
+
+
+class _FakeAsyncClient:
+    def __init__(self, responses: list[_MockStreamResp]):
+        self._responses = responses
+
+    async def __aenter__(self):
+        return self
+
+    async def __aexit__(self, exc_type, exc, tb):
+        return None
+
+    def stream(self, method, url, headers=None):
+        if not self._responses:
+            return _FakeStreamCtx(_MockStreamResp(404))
+        return _FakeStreamCtx(self._responses.pop(0))
+
+
+@contextmanager
+def _fake_httpx_sys_modules(client):
+    """Minimal ``httpx`` stub so ``download_img`` can be exercised without real httpx."""
+    saved = sys.modules.get("httpx")
+    fake = types.ModuleType("httpx")
+
+    class _Timeout:
+        def __init__(self, *_a, **_kw):
+            pass
+
+    fake.Timeout = _Timeout
+
+    def _AsyncClient(*_a, **_kw):
+        return client
+
+    fake.AsyncClient = _AsyncClient
+    sys.modules["httpx"] = fake
+    try:
+        yield
+    finally:
+        if saved is not None:
+            sys.modules["httpx"] = saved
+        else:
+            sys.modules.pop("httpx", None)
 
 
 class TestGetUuid:
@@ -92,16 +178,68 @@ class TestGetUuid:
 class TestDownloadImg:
     """Test cases for download_img function"""
 
-    @pytest.mark.asyncio
-    async def test_empty_url_returns_empty_string(self):
+    def test_empty_url_returns_empty_string(self):
         """Test that empty URL returns empty string"""
-        result = await download_img("")
+        result = asyncio.run(download_img(""))
         assert result == ""
 
-    @pytest.mark.asyncio
-    async def test_none_url_returns_empty_string(self):
+    def test_none_url_returns_empty_string(self):
         """Test that None URL returns empty string"""
-        result = await download_img(None)
+        result = asyncio.run(download_img(None))
+        assert result == ""
+
+    def test_loopback_url_blocked(self):
+        """OAuth avatar fetch must not call loopback (SSRF regression)."""
+        result = asyncio.run(download_img("http://127.0.0.1/avatar.png"))
+        assert result == ""
+
+    def test_metadata_ip_blocked(self):
+        """Link-local / cloud metadata ranges are non-global and must be rejected."""
+        result = asyncio.run(download_img("http://169.254.169.254/latest/meta-data/"))
+        assert result == ""
+
+    def test_disallowed_scheme_blocked(self):
+        result = asyncio.run(download_img("file:///etc/passwd"))
+        assert result == ""
+
+    def test_redirect_to_loopback_blocked(self):
+        """Redirect from an allowed host to loopback must be rejected (SSRF)."""
+        from urllib.parse import urlparse
+
+        real_assert = ssrf_guard.assert_url_is_safe
+
+        def selective_assert(url: str, **kwargs):
+            host = urlparse(url).hostname or ""
+            if host in ("127.0.0.1", "localhost", "169.254.169.254"):
+                return real_assert(url, **kwargs)
+            return ("public-avatar.test", "8.8.8.8")
+
+        client = _FakeAsyncClient([_MockStreamResp(302, location="http://127.0.0.1/next")])
+
+        with (
+            patch.object(ssrf_guard, "assert_url_is_safe", side_effect=selective_assert),
+            _fake_httpx_sys_modules(client),
+        ):
+            result = asyncio.run(download_img("http://public-avatar.test/start.png"))
+        assert result == ""
+
+    def test_redirect_too_many_hops_blocked(self):
+        """Excessive redirect chains must return empty without hanging."""
+        import common.misc_utils as misc_utils
+
+        hops = [
+            _MockStreamResp(302, location="http://h.example/1"),
+            _MockStreamResp(302, location="http://h.example/2"),
+            _MockStreamResp(302, location="http://h.example/3"),
+        ]
+        client = _FakeAsyncClient(hops)
+
+        with (
+            patch.object(misc_utils, "_OAUTH_AVATAR_MAX_REDIRECTS", 2),
+            patch.object(ssrf_guard, "assert_url_is_safe", return_value=("h.example", "8.8.8.8")),
+            _fake_httpx_sys_modules(client),
+        ):
+            result = asyncio.run(misc_utils.download_img("http://h.example/start"))
         assert result == ""