From 7621d8e6d6c926d1961a66af6255aa02f5f6c1cb Mon Sep 17 00:00:00 2001
From: Stefan <96178532+stefan6419846@users.noreply.github.com>
Date: Thu, 7 Dec 2023 09:49:32 +0100
Subject: [PATCH 1/4] BUG: Relax flate decoding for too many lookup values

---
 pypdf/_xobj_image_helpers.py | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/pypdf/_xobj_image_helpers.py b/pypdf/_xobj_image_helpers.py
index 515c01ebe..577979db3 100644
--- a/pypdf/_xobj_image_helpers.py
+++ b/pypdf/_xobj_image_helpers.py
@@ -195,7 +195,14 @@ def bits2byte(data: bytes, size: Tuple[int, int], bits: int) -> bytes:
         else:
             if img.mode == "1":
                 # Two values ("high" and "low").
-                assert len(lookup) == 2 * nb, len(lookup)
+                if len(lookup) != 2 * nb:
+                    if len(lookup) < 2 * nb:
+                        raise PdfReadError(f"Not enough lookup values: Expected {2 * nb}, got {len(lookup)}.")
+                    logger_warning(
+                        f"Expected {2 * nb} lookup values, got {len(lookup)}. Ignoring trailing ones.",
+                        __name__,
+                    )
+                    lookup = lookup[:2 * nb]
                 colors_arr = [lookup[:nb], lookup[nb:]]
                 arr = b"".join(
                     [

From 676abc891069c1f550ae037e9c8886efba8fee2c Mon Sep 17 00:00:00 2001
From: Stefan <96178532+stefan6419846@users.noreply.github.com>
Date: Fri, 8 Dec 2023 08:52:35 +0100
Subject: [PATCH 2/4] only accept whitespace characters as trailing ones

---
 pypdf/_xobj_image_helpers.py | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/pypdf/_xobj_image_helpers.py b/pypdf/_xobj_image_helpers.py
index 577979db3..30b69aa9d 100644
--- a/pypdf/_xobj_image_helpers.py
+++ b/pypdf/_xobj_image_helpers.py
@@ -4,7 +4,7 @@
 from io import BytesIO
 from typing import Any, List, Tuple, Union, cast
 
-from ._utils import logger_warning
+from ._utils import logger_warning, WHITESPACES
 from .constants import ColorSpaces
 from .errors import PdfReadError
 from .generic import (
@@ -195,14 +195,13 @@ def bits2byte(data: bytes, size: Tuple[int, int], bits: int) -> bytes:
         else:
             if img.mode == "1":
                 # Two values ("high" and "low").
-                if len(lookup) != 2 * nb:
-                    if len(lookup) < 2 * nb:
-                        raise PdfReadError(f"Not enough lookup values: Expected {2 * nb}, got {len(lookup)}.")
-                    logger_warning(
-                        f"Expected {2 * nb} lookup values, got {len(lookup)}. Ignoring trailing ones.",
-                        __name__,
-                    )
-                    lookup = lookup[:2 * nb]
+                expected_count = 2 * nb
+                if len(lookup) != expected_count:
+                    if len(lookup) < expected_count:
+                        raise PdfReadError(f"Not enough lookup values: Expected {expected_count}, got {len(lookup)}.")
+                    lookup = lookup[:expected_count]
+                    if not all(_value in WHITESPACES for _value in lookup[expected_count:]):
+                        raise PdfReadError(f"Too many lookup values: Expected {expected_count}, got {len(lookup)}.")
                 colors_arr = [lookup[:nb], lookup[nb:]]
                 arr = b"".join(
                     [

From c34e9fc5f68ff65d2aa941c377a78ecce3666762 Mon Sep 17 00:00:00 2001
From: Stefan <96178532+stefan6419846@users.noreply.github.com>
Date: Fri, 8 Dec 2023 08:55:21 +0100
Subject: [PATCH 3/4] fix import sort oder

---
 pypdf/_xobj_image_helpers.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pypdf/_xobj_image_helpers.py b/pypdf/_xobj_image_helpers.py
index 30b69aa9d..a390357dd 100644
--- a/pypdf/_xobj_image_helpers.py
+++ b/pypdf/_xobj_image_helpers.py
@@ -4,7 +4,7 @@
 from io import BytesIO
 from typing import Any, List, Tuple, Union, cast
 
-from ._utils import logger_warning, WHITESPACES
+from ._utils import WHITESPACES, logger_warning
 from .constants import ColorSpaces
 from .errors import PdfReadError
 from .generic import (

From 73308dc17659d02f4b0ea25c5a8c3204c6960db2 Mon Sep 17 00:00:00 2001
From: Stefan <96178532+stefan6419846@users.noreply.github.com>
Date: Fri, 8 Dec 2023 08:58:16 +0100
Subject: [PATCH 4/4] add test with trailing newline

---
 tests/test_filters.py | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tests/test_filters.py b/tests/test_filters.py
index 00a548ab0..72d6f76cc 100644
--- a/tests/test_filters.py
+++ b/tests/test_filters.py
@@ -649,3 +649,12 @@ def test_flate_decode_with_image_mode_1():
     reader = PdfReader(BytesIO(get_data_from_url(url, name=name)))
     for image in reader.pages[7].images:
         _ = image
+
+
+@pytest.mark.enable_socket()
+def test_flate_decode_with_image_mode_1__whitespace_at_end_of_lookup():
+    """From #2331"""
+    url = "https://github.com/py-pdf/pypdf/files/13611048/out1.pdf"
+    name = "issue2331.pdf"
+    reader = PdfReader(BytesIO(get_data_from_url(url, name=name)))
+    reader.pages[0].images[0]