diff --git a/Lib/test/test_unicodedata.py b/Lib/test/test_unicodedata.py
index 3f569e6baee676..0ffedd195b5017 100644
--- a/Lib/test/test_unicodedata.py
+++ b/Lib/test/test_unicodedata.py
@@ -617,7 +617,7 @@ def test_issue10254(self):
         self.assertEqual(self.db.normalize('NFC', a), b)
 
     def test_long_combining_mark_run(self):
-        # GH-XXXXX: avoid quadratic canonical ordering.
+        # gh-149079: avoid quadratic canonical ordering.
         payload = "a" + ("\u0300\u0327" * 32)
         nfd = "a" + ("\u0327" * 32) + ("\u0300" * 32)
         nfc = "\u00e0" + ("\u0327" * 32) + ("\u0300" * 31)
@@ -628,7 +628,7 @@ def test_long_combining_mark_run(self):
         self.assertEqual(self.db.normalize("NFKC", payload), nfc)
 
     def test_combining_mark_run_fast_paths(self):
-        # GH-XXXXX: cover short runs and already-sorted long runs.
+        # gh-149079: cover short runs and already-sorted long runs.
         short_payload = "a" + ("\u0300\u0327" * 9) + "\u0300"
         short_nfd = "a" + ("\u0327" * 9) + ("\u0300" * 10)
         short_nfc = "\u00e0" + ("\u0327" * 9) + ("\u0300" * 9)
diff --git a/Misc/NEWS.d/next/Security/2026-04-27-16-36-11.gh-issue-149079.vKl-LM.rst b/Misc/NEWS.d/next/Security/2026-04-27-16-36-11.gh-issue-149079.vKl-LM.rst
index 72e8374acffb1f..4ed22b58f7405f 100644
--- a/Misc/NEWS.d/next/Security/2026-04-27-16-36-11.gh-issue-149079.vKl-LM.rst
+++ b/Misc/NEWS.d/next/Security/2026-04-27-16-36-11.gh-issue-149079.vKl-LM.rst
@@ -1,5 +1,5 @@
 Fix a potential denial of service in :func:`unicodedata.normalize`. The
-canonical ordering step of Unicode normalization used an O(n²) insertion
+canonical ordering step of Unicode normalization used a quadratic-time insertion
 sort for reordering combining characters, which could be exploited with
 crafted input containing many combining characters in non-canonical order.
 Replaced with a linear-time counting sort for long runs.
diff --git a/Modules/unicodedata.c b/Modules/unicodedata.c
index 9ac2faffb40bfb..d132e77030bf29 100644
--- a/Modules/unicodedata.c
+++ b/Modules/unicodedata.c
@@ -586,22 +586,14 @@ canonical_ordering_sort_counting(int kind, void *data,
     Py_ssize_t counts[256] = {0};
     Py_ssize_t run_length = end - start;
     Py_ssize_t total = 0;
-    unsigned char min_combining = 255;
-    unsigned char max_combining = 0;
 
     for (Py_ssize_t i = start; i < end; i++) {
         Py_UCS4 code = PyUnicode_READ(kind, data, i);
         unsigned char combining = _getrecord_ex(code)->combining;
         counts[combining]++;
-        if (combining < min_combining) {
-            min_combining = combining;
-        }
-        if (combining > max_combining) {
-            max_combining = combining;
-        }
     }
 
-    for (Py_ssize_t i = min_combining; i <= max_combining; i++) {
+    for (size_t i = 0; i < Py_ARRAY_LENGTH(counts); i++) {
         Py_ssize_t count = counts[i];
         counts[i] = total;
         total += count;
@@ -629,7 +621,7 @@ nfd_nfkd(PyObject *self, PyObject *input, int k)
     void *result_data;
     /* Longest decomposition in Unicode 3.2: U+FDFA */
     Py_UCS4 stack[20];
-    Py_ssize_t space, isize, length;
+    Py_ssize_t space, isize;
     int index, prefix, count, stackptr;
     unsigned char prev, cur;
     Py_UCS4 *sortbuf = NULL;
@@ -727,25 +719,24 @@ nfd_nfkd(PyObject *self, PyObject *input, int k)
 
     result_kind = PyUnicode_KIND(result);
     result_data = PyUnicode_DATA(result);
-    length = PyUnicode_GET_LENGTH(result);
 
     /* Sort each consecutive combining-character run canonically. */
     i = 0;
-    while (i < length) {
+    while (i < o) {
         Py_ssize_t run_length, run_start;
         int needs_sort = 0;
 
-        prev = _getrecord_ex(
-            PyUnicode_READ(result_kind, result_data, i))->combining;
+        Py_UCS4 ch = PyUnicode_READ(result_kind, result_data, i);
+        prev = _getrecord_ex(ch)->combining;
         if (prev == 0) {
             i++;
             continue;
         }
 
         run_start = i++;
-        while (i < length) {
-            cur = _getrecord_ex(
-                PyUnicode_READ(result_kind, result_data, i))->combining;
+        while (i < o) {
+            Py_UCS4 ch = PyUnicode_READ(result_kind, result_data, i);
+            cur = _getrecord_ex(ch)->combining;
             if (cur == 0) {
                 break;
             }
@@ -767,8 +758,9 @@ nfd_nfkd(PyObject *self, PyObject *input, int k)
         }
 
         if (run_length > sortbuflen) {
-            Py_UCS4 *new_sortbuf = PyMem_Realloc(sortbuf,
-                                                 run_length * sizeof(Py_UCS4));
+            Py_UCS4 *new_sortbuf = PyMem_Resize(sortbuf,
+                                                Py_UCS4,
+                                                run_length);
             if (new_sortbuf == NULL) {
                 PyErr_NoMemory();
                 PyMem_Free(sortbuf);