diff --git a/Zend/zend_portability.h b/Zend/zend_portability.h
index 97bd038ecf3d8..7a41a496a0ed7 100644
--- a/Zend/zend_portability.h
+++ b/Zend/zend_portability.h
@@ -496,6 +496,8 @@ extern "C++" {
 
 #ifdef ZEND_WIN32
 #define ZEND_SECURE_ZERO(var, size) RtlSecureZeroMemory((var), (size))
+#elif defined(HAVE_MEMSET_EXPLICIT)
+#define ZEND_SECURE_ZERO(var, size) memset_explicit((var), 0, (size))
 #else
 #define ZEND_SECURE_ZERO(var, size) explicit_bzero((var), (size))
 #endif
diff --git a/configure.ac b/configure.ac
index f6f305ba053a8..e4a8c31de474f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -564,6 +564,7 @@ AC_CHECK_FUNCS(m4_normalize([
   memmem
   mempcpy
   memrchr
+  memset_explicit
   mkstemp
   mmap
   nice
diff --git a/ext/opcache/zend_accelerator_module.c b/ext/opcache/zend_accelerator_module.c
index 203a41d93b40a..a4f632872f546 100644
--- a/ext/opcache/zend_accelerator_module.c
+++ b/ext/opcache/zend_accelerator_module.c
@@ -323,7 +323,7 @@ ZEND_INI_BEGIN()
 	STD_PHP_INI_ENTRY("opcache.jit_max_root_traces"           , "1024",                       PHP_INI_SYSTEM, OnUpdateLong,     max_root_traces,       zend_jit_globals, jit_globals)
 	STD_PHP_INI_ENTRY("opcache.jit_max_side_traces"           , "128",                        PHP_INI_SYSTEM, OnUpdateLong,     max_side_traces,       zend_jit_globals, jit_globals)
 	STD_PHP_INI_ENTRY("opcache.jit_max_exit_counters"         , "8192",                       PHP_INI_SYSTEM, OnUpdateLong,     max_exit_counters,     zend_jit_globals, jit_globals)
-	/* Defautl value should be a prime number, to reduce the chances of loop iterations being a factor of opcache.jit_hot_loop */
+	/* Default value should be a prime number, to reduce the chances of loop iterations being a factor of opcache.jit_hot_loop */
 	STD_PHP_INI_ENTRY("opcache.jit_hot_loop"                  , "61",                         PHP_INI_SYSTEM, OnUpdateCounter,  hot_loop,              zend_jit_globals, jit_globals)
 	STD_PHP_INI_ENTRY("opcache.jit_hot_func"                  , "127",                        PHP_INI_SYSTEM, OnUpdateCounter,  hot_func,              zend_jit_globals, jit_globals)
 	STD_PHP_INI_ENTRY("opcache.jit_hot_return"                , "8",                          PHP_INI_SYSTEM, OnUpdateCounter,  hot_return,            zend_jit_globals, jit_globals)
diff --git a/ext/sqlite3/tests/sqlite3_explain.phpt b/ext/sqlite3/tests/sqlite3_explain.phpt
index f580783ca1d14..40648588733c6 100644
--- a/ext/sqlite3/tests/sqlite3_explain.phpt
+++ b/ext/sqlite3/tests/sqlite3_explain.phpt
@@ -79,7 +79,7 @@ array(%d) {
     ["addr"]=>
     int(1)
     ["opcode"]=>
-    string(13) "InitCoroutine"
+    string(%d) "%s"
     ["p1"]=>
     int(3)
     ["p2"]=>
@@ -87,7 +87,7 @@ array(%d) {
     ["p3"]=>
     int(2)
     ["p4"]=>
-    NULL
+    %s
     ["p5"]=>
     int(0)
     ["comment"]=>
@@ -368,7 +368,7 @@ array(1) {
     ["parent"]=>
     int(0)
     ["notused"]=>
-    int(0)
+    int(%d)
     ["detail"]=>
     string(17) "SCAN test_explain"
   }
diff --git a/ext/standard/pack.c b/ext/standard/pack.c
index d4c5cc1f04cfa..bcac949d56329 100644
--- a/ext/standard/pack.c
+++ b/ext/standard/pack.c
@@ -366,7 +366,7 @@ PHP_FUNCTION(pack)
 		switch (code) {
 			case 'h':
 			case 'H':
-				INC_OUTPUTPOS((arg + (arg % 2)) / 2,1)	/* 4 bit per arg */
+				INC_OUTPUTPOS((arg / 2) + (arg % 2),1)	/* 4 bit per arg */
 				break;
 
 			case 'a':
diff --git a/ext/standard/tests/strings/gh18976.phpt b/ext/standard/tests/strings/gh18976.phpt
new file mode 100644
index 0000000000000..aa58167f9d45b
--- /dev/null
+++ b/ext/standard/tests/strings/gh18976.phpt
@@ -0,0 +1,14 @@
+--TEST--
+GH-18976 (pack overflow with h/H format)
+--INI--
+memory_limit=-1
+--FILE--
+<?php
+pack('h2147483647', 1);
+pack('H2147483647', 1);
+?>
+--EXPECTF--
+
+Warning: pack(): Type h: not enough characters in string in %s on line %d
+
+Warning: pack(): Type H: not enough characters in string in %s on line %d
diff --git a/main/explicit_bzero.c b/main/explicit_bzero.c
index 75cd126ee9a56..c49bdede66247 100644
--- a/main/explicit_bzero.c
+++ b/main/explicit_bzero.c
@@ -28,8 +28,10 @@
 
 PHPAPI void php_explicit_bzero(void *dst, size_t siz)
 {
-#ifdef HAVE_EXPLICIT_MEMSET
-    explicit_memset(dst, 0, siz);
+#ifdef HAVE_MEMSET_EXPLICIT /* C23 */
+	memset_explicit(dst, 0, siz);
+#elif defined(HAVE_EXPLICIT_MEMSET) /* NetBSD-specific */
+	explicit_memset(dst, 0, siz);
 #elif defined(PHP_WIN32)
 	RtlSecureZeroMemory(dst, siz);
 #elif defined(__GNUC__)