Origin: https://github.com/python-pillow/Pillow/pull/7655

From 45c726fd4daa63236a8f3653530f297dc87b160a Mon Sep 17 00:00:00 2001
From: Eric Soroos <eric-github@soroos.net>
Date: Fri, 27 Oct 2023 11:21:18 +0200
Subject: [PATCH 1/3] Don't allow __ or builtins in env dictionarys for
 ImageMath.eval

---
 src/PIL/ImageMath.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/PIL/ImageMath.py b/src/PIL/ImageMath.py
index 7ca512e7568..cf108e2586f 100644
--- a/src/PIL/ImageMath.py
+++ b/src/PIL/ImageMath.py
@@ -237,6 +237,10 @@ def eval(expression, _dict={}, **kw):
     args.update(_dict)
     args.update(kw)
-    for k, v in list(args.items()):
+    for k, v in args.items():
+        if '__' in k or hasattr(__builtins__, k):
+            msg = f"'{k}' not allowed"
+            raise ValueError(msg)
+
         if hasattr(v, "im"):
             args[k] = _Operand(v)
 

From 0ca3c33c59927e1c7e0c14dbc1eea1dfb2431a80 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Sat, 28 Oct 2023 15:58:52 +1100
Subject: [PATCH 2/3] Allow ops

---
 Tests/test_imagemath.py | 5 +++++
 src/PIL/ImageMath.py    | 9 +++++----
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/Tests/test_imagemath.py b/Tests/test_imagemath.py
index 22de86c7cab..9a0326ece3b 100644
--- a/Tests/test_imagemath.py
+++ b/Tests/test_imagemath.py
@@ -64,6 +64,11 @@ def test_prevent_exec(expression):
         ImageMath.eval(expression)
 
 
+def test_prevent_double_underscores():
+    with pytest.raises(ValueError):
+        ImageMath.eval("1", {"__": None})
+
+
 def test_logical():
     assert pixel(ImageMath.eval("not A", images)) == 0
     assert pixel(ImageMath.eval("A and B", images)) == "L 2"
diff --git a/src/PIL/ImageMath.py b/src/PIL/ImageMath.py
index cf108e2586f..fd7d78d4583 100644
--- a/src/PIL/ImageMath.py
+++ b/src/PIL/ImageMath.py
@@ -234,13 +234,14 @@ def eval(expression, _dict={}, **kw):
 
     # build execution namespace
     args = ops.copy()
-    args.update(_dict)
-    args.update(kw)
-    for k, v in args.items():
-        if '__' in k or hasattr(__builtins__, k):
+    for k in list(_dict.keys()) + list(kw.keys()):
+        if "__" in k or hasattr(__builtins__, k):
             msg = f"'{k}' not allowed"
             raise ValueError(msg)
 
+    args.update(_dict)
+    args.update(kw)
+    for k, v in args.items():
         if hasattr(v, "im"):
             args[k] = _Operand(v)
 

From 557ba59d13de919d04b3fd4cdef8634f7d4b3348 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Sat, 30 Dec 2023 09:30:12 +1100
Subject: [PATCH 3/3] Include further builtins

---
 Tests/test_imagemath.py      | 5 +++++
 docs/releasenotes/10.2.0.rst | 9 ++++++---
 src/PIL/ImageMath.py         | 2 +-
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/Tests/test_imagemath.py b/Tests/test_imagemath.py
index 9a0326ece3b..9281de6f66a 100644
--- a/Tests/test_imagemath.py
+++ b/Tests/test_imagemath.py
@@ -69,6 +69,11 @@ def test_prevent_double_underscores():
         ImageMath.eval("1", {"__": None})
 
 
+def test_prevent_builtins():
+    with pytest.raises(ValueError):
+        ImageMath.eval("(lambda: exec('exit()'))()", {"exec": None})
+
+
 def test_logical():
     assert pixel(ImageMath.eval("not A", images)) == 0
     assert pixel(ImageMath.eval("A and B", images)) == "L 2"
diff --git a/src/PIL/ImageMath.py b/src/PIL/ImageMath.py
index fd7d78d4583..b77f4bce567 100644
--- a/src/PIL/ImageMath.py
+++ b/src/PIL/ImageMath.py
@@ -235,7 +235,7 @@ def eval(expression, _dict={}, **kw):
     # build execution namespace
     args = ops.copy()
     for k in list(_dict.keys()) + list(kw.keys()):
-        if "__" in k or hasattr(__builtins__, k):
+        if "__" in k or hasattr(builtins, k):
             msg = f"'{k}' not allowed"
             raise ValueError(msg)
 
