From 98e2b7ea599625fbc75f28f20361b593f1013ace Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Sat, 6 Jun 2026 17:45:50 +1000
Subject: [PATCH] Validate size and rank when initializing RankFilter

---
 Tests/test_image_filter.py | 16 ++++++++++++++--
 src/PIL/ImageFilter.py     | 20 +++++++++++++-------
 2 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/Tests/test_image_filter.py b/Tests/test_image_filter.py
index e566cd0557a..5a7d3f90a0a 100644
--- a/Tests/test_image_filter.py
+++ b/Tests/test_image_filter.py
@@ -136,11 +136,23 @@ def test_rankfilter_error(filter: ImageFilter.RankFilter) -> None:
 
 
 def test_rankfilter_properties() -> None:
-    rankfilter = ImageFilter.RankFilter(1, 2)
+    rankfilter = ImageFilter.RankFilter(3, 2)
 
-    assert rankfilter.size == 1
+    assert rankfilter.size == 3
     assert rankfilter.rank == 2
 
+    with pytest.raises(ValueError, match="bad filter size"):
+        ImageFilter.RankFilter(2, 1)
+    with pytest.raises(ValueError, match="bad filter size"):
+        ImageFilter.MaxFilter(2)
+    with pytest.raises(ValueError, match="bad filter size"):
+        ImageFilter.MedianFilter(2)
+    with pytest.raises(ValueError, match="bad filter size"):
+        ImageFilter.MinFilter(2)
+
+    with pytest.raises(ValueError, match="bad rank value"):
+        ImageFilter.RankFilter(1, 1)
+
 
 def test_builtinfilter_p() -> None:
     builtin_filter = ImageFilter.BuiltinFilter()
diff --git a/src/PIL/ImageFilter.py b/src/PIL/ImageFilter.py
index 9326eeeda9d..a7aeff3040c 100644
--- a/src/PIL/ImageFilter.py
+++ b/src/PIL/ImageFilter.py
@@ -90,7 +90,7 @@ class RankFilter(Filter):
     Create a rank filter.  The rank filter sorts all pixels in
     a window of the given size, and returns the ``rank``'th value.
 
-    :param size: The kernel size, in pixels.
+    :param size: The kernel size, in pixels. Must be odd.
     :param rank: What pixel value to pick.  Use 0 for a min filter,
                  ``size * size / 2`` for a median filter, ``size * size - 1``
                  for a max filter, etc.
@@ -99,6 +99,12 @@ class RankFilter(Filter):
     name = "Rank"
 
     def __init__(self, size: int, rank: int) -> None:
+        if size % 2 == 0:
+            msg = "bad filter size"
+            raise ValueError(msg)
+        if rank < 0 or rank >= size * size:
+            msg = "bad rank value"
+            raise ValueError(msg)
         self.size = size
         self.rank = rank
 
@@ -121,8 +127,8 @@ class MedianFilter(RankFilter):
     name = "Median"
 
     def __init__(self, size: int = 3) -> None:
-        self.size = size
-        self.rank = size * size // 2
+        rank = size * size // 2
+        super().__init__(size, rank)
 
 
 class MinFilter(RankFilter):
@@ -136,8 +142,8 @@ class MinFilter(RankFilter):
     name = "Min"
 
     def __init__(self, size: int = 3) -> None:
-        self.size = size
-        self.rank = 0
+        rank = 0
+        super().__init__(size, rank)
 
 
 class MaxFilter(RankFilter):
@@ -151,8 +157,8 @@ class MaxFilter(RankFilter):
     name = "Max"
 
     def __init__(self, size: int = 3) -> None:
-        self.size = size
-        self.rank = size * size - 1
+        rank = size * size - 1
+        super().__init__(size, rank)
 
 
 class ModeFilter(Filter):