From fedb0407b4cd14a285fbc641761d9bc6a5348c37 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Thu, 26 Dec 2019 13:10:39 +1100
Subject: [PATCH] Raise ValueError for io.StringIO in Image.open

---
 Tests/test_image.py | 4 ++++
 src/PIL/Image.py    | 6 ++++++
 2 files changed, 10 insertions(+)

diff --git a/Tests/test_image.py b/Tests/test_image.py
index 83da76b96..47e7420ef 100644
--- a/Tests/test_image.py
+++ b/Tests/test_image.py
@@ -1,3 +1,4 @@
+import io
 import os
 import shutil
 import tempfile
@@ -91,6 +92,9 @@ class TestImage(PillowTestCase):
     def test_bad_mode(self):
         self.assertRaises(ValueError, Image.open, "filename", "bad mode")
 
+    def test_stringio(self):
+        self.assertRaises(ValueError, Image.open, io.StringIO())
+
     def test_pathlib(self):
         from PIL.Image import Path
 
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 41e9c9fe8..3827ab09d 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -2690,10 +2690,16 @@ def open(fp, mode="r"):
     :exception FileNotFoundError: If the file cannot be found.
     :exception PIL.UnidentifiedImageError: If the image cannot be opened and
        identified.
+    :exception ValueError: If the ``mode`` is not "r", or if a StringIO
+       instance is used for ``fp``.
     """
 
     if mode != "r":
         raise ValueError("bad mode %r" % mode)
+    elif isinstance(fp, io.StringIO):
+        raise ValueError(
+            "StringIO cannot be used to open an image. Binary data must be used instead"
+        )
 
     exclusive_fp = False
     filename = ""