diff --git a/CVE-2025-64076.patch b/CVE-2025-64076.patch
new file mode 100644
index 0000000..9e3ed57
--- /dev/null
+++ b/CVE-2025-64076.patch
@@ -0,0 +1,71 @@
+From 851473490281f82d82560b2368284ef33cf6e8f9 Mon Sep 17 00:00:00 2001
+From: lizhenghao <sculizhenghao@foxmail.com>
+Date: Wed, 22 Oct 2025 10:26:34 +0800
+Subject: [PATCH 1/3] Fix: Fixed a read(-1) vulnerability caused by boundary
+ handling error in #264
+
+---
+ source/decoder.c      |  8 +++++++-
+ tests/test_decoder.py | 22 ++++++++++++++++++++++
+ 2 files changed, 29 insertions(+), 1 deletion(-)
+
+Index: cbor2-5.6.5/source/decoder.c
+===================================================================
+--- cbor2-5.6.5.orig/source/decoder.c
++++ cbor2-5.6.5/source/decoder.c
+@@ -758,7 +758,7 @@ decode_definite_long_string(CBORDecoderO
+     char *buffer = NULL;
+     while (left) {
+         // Read up to 65536 bytes of data from the stream
+-        Py_ssize_t chunk_length = 65536 - buffer_size;
++        Py_ssize_t chunk_length = 65536 - buffer_length;
+         if (left < chunk_length)
+             chunk_length = left;
+ 
+@@ -828,7 +828,13 @@ decode_definite_long_string(CBORDecoderO
+                 memcpy(buffer, bytes_buffer + consumed, unconsumed);
+             }
+             buffer_length = unconsumed;
++        } else {
++            // All bytes consumed, reset buffer_length
++            buffer_length = 0;
+         }
++
++        Py_DECREF(chunk);
++        chunk = NULL;
+     }
+ 
+     if (ret && string_namespace_add(self, ret, length) == -1)
+Index: cbor2-5.6.5/tests/test_decoder.py
+===================================================================
+--- cbor2-5.6.5.orig/tests/test_decoder.py
++++ cbor2-5.6.5/tests/test_decoder.py
+@@ -260,6 +260,28 @@ def test_string_oversized(impl) -> None:
+         (impl.loads(unhexlify("aeaeaeaeaeaeaeaeae0108c29843d90100d8249f0000aeaeffc26ca799")),)
+ 
+ 
++def test_string_issue_264_multiple_chunks_utf8_boundary(impl) -> None:
++    """Test for Issue #264: UTF-8 characters split across multiple 65536-byte chunk boundaries."""
++    import struct
++
++    # Construct: 65535 'a' + '€' (3 bytes) + 65533 'b' + '€' (3 bytes) + 100 'd'
++    # Total: 131174 bytes, which spans 3 chunks (65536 + 65536 + 102)
++    total_bytes = 65535 + 3 + 65533 + 3 + 100
++
++    payload = b"\x7a" + struct.pack(">I", total_bytes)  # major type 3, 4-byte length
++    payload += b"a" * 65535
++    payload += "€".encode()  # U+20AC: E2 82 AC
++    payload += b"b" * 65533
++    payload += "€".encode()
++    payload += b"d" * 100
++
++    expected = "a" * 65535 + "€" + "b" * 65533 + "€" + "d" * 100
++
++    result = impl.loads(payload)
++    assert result == expected
++    assert len(result) == 131170  # 65535 + 1 + 65533 + 1 + 100 characters
++
++
+ @pytest.mark.parametrize(
+     "payload, expected",
+     [
diff --git a/python-cbor2.changes b/python-cbor2.changes
index ac162ef..7753e7a 100644
--- a/python-cbor2.changes
+++ b/python-cbor2.changes
@@ -1,3 +1,11 @@
+-------------------------------------------------------------------
+Wed Nov 19 10:56:07 UTC 2025 - Daniel Garcia <daniel.garcia@suse.com>
+
+- Add CVE-2025-64076.patch from upstream. Fix: bug in
+  decode_definite_long_string() that causes incorrect chunk length
+  calculation
+  (bsc#1253746, CVE-2025-64076, gh#agronholm/cbor2#265)
+
 -------------------------------------------------------------------
 Tue Oct 22 13:48:00 UTC 2024 - Dirk Müller <dmueller@suse.com>
 
diff --git a/python-cbor2.spec b/python-cbor2.spec
index 203a2f6..602af70 100644
--- a/python-cbor2.spec
+++ b/python-cbor2.spec
@@ -24,6 +24,8 @@ Summary:        Pure Python CBOR (de)serializer with extensive tag support
 License:        MIT
 URL:            https://github.com/agronholm/cbor2
 Source:         https://files.pythonhosted.org/packages/source/c/cbor2/cbor2-%{version}.tar.gz
+# PATCH-FIX-UPSTREAM CVE-2025-64076.patch bsc#1253746 gh#agronholm/cbor2#265
+Patch0:         CVE-2025-64076.patch
 BuildRequires:  %{python_module devel}
 BuildRequires:  %{python_module hypothesis}
 BuildRequires:  %{python_module pip}