From 83cdcc0dadb4a044d7c10b0a64a6853d0889ee74 Mon Sep 17 00:00:00 2001
From: Jiseok CHOI <jiseok.dev@gmail.com>
Date: Thu, 4 Jun 2026 22:41:47 +0900
Subject: [PATCH] gh-150913: Fix sqlite3.Blob validation for empty slice
 assignment (GH-150915)

ass_subscript_slice() returned early when the computed slice length
was zero, bypassing validation performed for non-empty slices.
(cherry picked from commit fc9c4db1302f8be7527e70cf0938b629985a1d72)

Co-authored-by: Jiseok CHOI <jiseok.dev@gmail.com>
---
 Lib/test/test_sqlite3/test_dbapi.py              | 12 ++++++++++++
 ...26-06-04-21-49-18.gh-issue-150913.EmptyBl.rst |  3 +++
 Modules/_sqlite/blob.c                           | 16 ++++++++++------
 3 files changed, 25 insertions(+), 6 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-06-04-21-49-18.gh-issue-150913.EmptyBl.rst

diff --git a/Lib/test/test_sqlite3/test_dbapi.py b/Lib/test/test_sqlite3/test_dbapi.py
index 73b40e82a96811f..5f6cb527955ca17 100644
--- a/Lib/test/test_sqlite3/test_dbapi.py
+++ b/Lib/test/test_sqlite3/test_dbapi.py
@@ -1400,6 +1400,18 @@ def test_blob_set_empty_slice(self):
         self.blob[0:0] = b""
         self.assertEqual(self.blob[:], self.data)
 
+    def test_blob_set_empty_slice_wrong_type(self):
+        with self.assertRaises(TypeError):
+            self.blob[5:5] = None
+
+    def test_blob_set_empty_slice_wrong_size(self):
+        with self.assertRaisesRegex(IndexError, "wrong size"):
+            self.blob[5:5] = b"123"
+
+    def test_blob_set_empty_slice_correct(self):
+        self.blob[5:5] = b""
+        self.assertEqual(self.blob[:], self.data)
+
     def test_blob_set_slice_with_skip(self):
         self.blob[0:10:2] = b"12345"
         actual = self.cx.execute("select b from test").fetchone()[0]
diff --git a/Misc/NEWS.d/next/Library/2026-06-04-21-49-18.gh-issue-150913.EmptyBl.rst b/Misc/NEWS.d/next/Library/2026-06-04-21-49-18.gh-issue-150913.EmptyBl.rst
new file mode 100644
index 000000000000000..f95a6ee6ee15bf7
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-06-04-21-49-18.gh-issue-150913.EmptyBl.rst
@@ -0,0 +1,3 @@
+Fix :class:`sqlite3.Blob` slice assignment to raise
+:exc:`TypeError` and :exc:`IndexError` for type and size mismatches
+respectively, even when the target slice is empty.
diff --git a/Modules/_sqlite/blob.c b/Modules/_sqlite/blob.c
index 2cc62751054278f..d81784409e5d91a 100644
--- a/Modules/_sqlite/blob.c
+++ b/Modules/_sqlite/blob.c
@@ -531,21 +531,25 @@ ass_subscript_slice(pysqlite_Blob *self, PyObject *item, PyObject *value)
         return -1;
     }
 
-    if (len == 0) {
-        return 0;
-    }
-
     Py_buffer vbuf;
     if (PyObject_GetBuffer(value, &vbuf, PyBUF_SIMPLE) < 0) {
         return -1;
     }
 
-    int rc = -1;
     if (vbuf.len != len) {
         PyErr_SetString(PyExc_IndexError,
                         "Blob slice assignment is wrong size");
+        PyBuffer_Release(&vbuf);
+        return -1;
     }
-    else if (step == 1) {
+
+    if (len == 0) {
+        PyBuffer_Release(&vbuf);
+        return 0;
+    }
+
+    int rc = -1;
+    if (step == 1) {
         rc = inner_write(self, vbuf.buf, len, start);
     }
     else {