diff --git a/NEWS b/NEWS
index ee9ee810b2565..145a1d9a5cb56 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,9 @@ PHP                                                                        NEWS
   . ext/bcmath: Check for scale overflow. (SakiTakamachi)
   . [RFC] ext/bcmath: Added bcdivmod. (SakiTakamachi)
 
+- Curl:
+  . Added CURLOPT_DEBUGFUNCTION as a Curl option. (Ayesh Karunaratne)
+
 - Debugging:
   . Fixed bug GH-15923 (GDB: Python Exception <class 'TypeError'>:
     exceptions must derive from BaseException). (nielsdos)
diff --git a/UPGRADING b/UPGRADING
index 97740040a0e90..3c40a708ed4fc 100644
--- a/UPGRADING
+++ b/UPGRADING
@@ -302,6 +302,13 @@ PHP 8.4 UPGRADE NOTES
     to allow or abort the request.
   . Added CURLOPT_SERVER_RESPONSE_TIMEOUT, which was formerly known as
     CURLOPT_FTP_RESPONSE_TIMEOUT. Both constants hold the same value.
+  . Added CURLOPT_DEBUGFUNCTION support. This Curl option accepts a callable
+    that gets called during the request lifetime with the CurlHandle object,
+    an integer containing the debug message type, and a string containing the
+    debug message. The debug message type is one of CURLINFO_TEXT, CURLINFO_HEADER_IN,
+    CURLINFO_HEADER_OUT, CURLINFO_DATA_IN, CURLINFO_DATA_OUT, CURLINFO_SSL_DATA_OUT,
+    CURLINFO_SSL_DATA_IN constants. Once this option is set, CURLINFO_HEADER_OUT
+    must not be set because it uses the same libcurl functionality.
 
 - Date:
   . Added static methods
@@ -1041,6 +1048,13 @@ PHP 8.4 UPGRADE NOTES
   . CURL_PREREQFUNC_OK.
   . CURL_PREREQFUNC_ABORT.
   . CURLOPT_SERVER_RESPONSE_TIMEOUT.
+  . CURLOPT_DEBUGFUNCTION.
+  . CURLINFO_TEXT.
+  . CURLINFO_HEADER_IN.
+  . CURLINFO_DATA_IN.
+  . CURLINFO_DATA_OUT.
+  . CURLINFO_SSL_DATA_OUT.
+  . CURLINFO_SSL_DATA_IN.
 
 - Intl:
   . The IntlDateFormatter class exposes now the new PATTERN constant
diff --git a/ext/curl/curl.stub.php b/ext/curl/curl.stub.php
index e6245aab073e2..3cd442674573b 100644
--- a/ext/curl/curl.stub.php
+++ b/ext/curl/curl.stub.php
@@ -486,6 +486,48 @@
  */
 const CURLOPT_XFERINFOFUNCTION = UNKNOWN;
 
+/**
+ * @var int
+ * @cvalue CURLOPT_DEBUGFUNCTION
+ */
+const CURLOPT_DEBUGFUNCTION = UNKNOWN;
+
+/**
+ * @var int
+ * @cvalue CURLINFO_TEXT
+ */
+const CURLINFO_TEXT = UNKNOWN;
+
+/**
+ * @var int
+ * @cvalue CURLINFO_HEADER_IN
+ */
+const CURLINFO_HEADER_IN = UNKNOWN;
+
+/**
+ * @var int
+ * @cvalue CURLINFO_DATA_IN
+ */
+const CURLINFO_DATA_IN = UNKNOWN;
+
+/**
+ * @var int
+ * @cvalue CURLINFO_DATA_OUT
+ */
+const CURLINFO_DATA_OUT = UNKNOWN;
+
+/**
+ * @var int
+ * @cvalue CURLINFO_SSL_DATA_OUT
+ */
+const CURLINFO_SSL_DATA_OUT = UNKNOWN;
+
+/**
+ * @var int
+ * @cvalue CURLINFO_SSL_DATA_IN
+ */
+const CURLINFO_SSL_DATA_IN = UNKNOWN;
+
 /* */
 /**
  * @var int
diff --git a/ext/curl/curl_arginfo.h b/ext/curl/curl_arginfo.h
index 99db69c3f7856..b472bafe8737a 100644
--- a/ext/curl/curl_arginfo.h
+++ b/ext/curl/curl_arginfo.h
@@ -1,5 +1,5 @@
 /* This is a generated file, edit the .stub.php file instead.
- * Stub hash: 5aa5f230880f8373ef8ec378f7e600247332136e */
+ * Stub hash: c5e16a7da3f25d061813235a262501e0d8747ccb */
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_curl_close, 0, 1, IS_VOID, 0)
 	ZEND_ARG_OBJ_INFO(0, handle, CurlHandle, 0)
@@ -312,6 +312,13 @@ static void register_curl_symbols(int module_number)
 	REGISTER_LONG_CONSTANT("CURLOPT_WRITEFUNCTION", CURLOPT_WRITEFUNCTION, CONST_PERSISTENT);
 	REGISTER_LONG_CONSTANT("CURLOPT_WRITEHEADER", CURLOPT_WRITEHEADER, CONST_PERSISTENT);
 	REGISTER_LONG_CONSTANT("CURLOPT_XFERINFOFUNCTION", CURLOPT_XFERINFOFUNCTION, CONST_PERSISTENT);
+	REGISTER_LONG_CONSTANT("CURLOPT_DEBUGFUNCTION", CURLOPT_DEBUGFUNCTION, CONST_PERSISTENT);
+	REGISTER_LONG_CONSTANT("CURLINFO_TEXT", CURLINFO_TEXT, CONST_PERSISTENT);
+	REGISTER_LONG_CONSTANT("CURLINFO_HEADER_IN", CURLINFO_HEADER_IN, CONST_PERSISTENT);
+	REGISTER_LONG_CONSTANT("CURLINFO_DATA_IN", CURLINFO_DATA_IN, CONST_PERSISTENT);
+	REGISTER_LONG_CONSTANT("CURLINFO_DATA_OUT", CURLINFO_DATA_OUT, CONST_PERSISTENT);
+	REGISTER_LONG_CONSTANT("CURLINFO_SSL_DATA_OUT", CURLINFO_SSL_DATA_OUT, CONST_PERSISTENT);
+	REGISTER_LONG_CONSTANT("CURLINFO_SSL_DATA_IN", CURLINFO_SSL_DATA_IN, CONST_PERSISTENT);
 	REGISTER_LONG_CONSTANT("CURLE_ABORTED_BY_CALLBACK", CURLE_ABORTED_BY_CALLBACK, CONST_PERSISTENT);
 	REGISTER_LONG_CONSTANT("CURLE_BAD_CALLING_ORDER", CURLE_BAD_CALLING_ORDER, CONST_PERSISTENT);
 	REGISTER_LONG_CONSTANT("CURLE_BAD_CONTENT_ENCODING", CURLE_BAD_CONTENT_ENCODING, CONST_PERSISTENT);
diff --git a/ext/curl/curl_private.h b/ext/curl/curl_private.h
index 011c4874e6140..19e43094574de 100644
--- a/ext/curl/curl_private.h
+++ b/ext/curl/curl_private.h
@@ -68,6 +68,7 @@ typedef struct {
 	zend_fcall_info_cache progress;
 	zend_fcall_info_cache xferinfo;
 	zend_fcall_info_cache fnmatch;
+	zend_fcall_info_cache debug;
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 	zend_fcall_info_cache prereq;
 #endif
diff --git a/ext/curl/interface.c b/ext/curl/interface.c
index 3006b67dfce6d..540d326169e86 100644
--- a/ext/curl/interface.c
+++ b/ext/curl/interface.c
@@ -504,6 +504,10 @@ static HashTable *curl_get_gc(zend_object *object, zval **table, int *n)
 		zend_get_gc_buffer_add_fcc(gc_buffer, &curl->handlers.fnmatch);
 	}
 
+	if (ZEND_FCC_INITIALIZED(curl->handlers.debug)) {
+		zend_get_gc_buffer_add_fcc(gc_buffer, &curl->handlers.debug);
+	}
+
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 	if (ZEND_FCC_INITIALIZED(curl->handlers.prereq)) {
 		zend_get_gc_buffer_add_fcc(gc_buffer, &curl->handlers.prereq);
@@ -915,18 +919,46 @@ static size_t curl_write_header(char *data, size_t size, size_t nmemb, void *ctx
 }
 /* }}} */
 
-static int curl_debug(CURL *cp, curl_infotype type, char *buf, size_t buf_len, void *ctx) /* {{{ */
+static int curl_debug(CURL *handle, curl_infotype type, char *data, size_t size, void *clientp) /* {{{ */
 {
-	php_curl *ch = (php_curl *)ctx;
+	php_curl *ch = (php_curl *)clientp;
 
-	if (type == CURLINFO_HEADER_OUT) {
-		if (ch->header.str) {
-			zend_string_release_ex(ch->header.str, 0);
-		}
-		ch->header.str = zend_string_init(buf, buf_len, 0);
-	}
+    #if PHP_CURL_DEBUG
+    	fprintf(stderr, "curl_debug() called\n");
+    	fprintf(stderr, "type = %d, data = %s\n", type, data);
+    #endif
+
+	// Implicitly store the headers for compatibility with CURLINFO_HEADER_OUT
+	// used as a Curl option. Previously, setting CURLINFO_HEADER_OUT set curl_debug
+	// as the CURLOPT_DEBUGFUNCTION and stored the debug data when type is set to
+	// CURLINFO_HEADER_OUT. For backward compatibility, we now store the headers
+	// but also call the user-callback function if available.
+    if (type == CURLINFO_HEADER_OUT) {
+    	if (ch->header.str) {
+    		zend_string_release_ex(ch->header.str, 0);
+    	}
+    	ch->header.str = zend_string_init(data, size, 0);
+    }
+
+    if (!ZEND_FCC_INITIALIZED(ch->handlers.debug)) {
+       	return 0;
+    }
 
-	return 0;
+    zval args[3];
+
+    GC_ADDREF(&ch->std);
+    ZVAL_OBJ(&args[0], &ch->std);
+    ZVAL_LONG(&args[1], type);
+    ZVAL_STRINGL(&args[2], data, size);
+
+    ch->in_callback = true;
+    zend_call_known_fcc(&ch->handlers.debug, NULL, /* param_count */ 3, args, /* named_params */ NULL);
+    ch->in_callback = false;
+
+    zval_ptr_dtor(&args[0]);
+    zval_ptr_dtor(&args[2]);
+
+    return 0;
 }
 /* }}} */
 
@@ -1096,6 +1128,7 @@ void init_curl_handle(php_curl *ch)
 	ch->handlers.progress = empty_fcall_info_cache;
 	ch->handlers.xferinfo = empty_fcall_info_cache;
 	ch->handlers.fnmatch = empty_fcall_info_cache;
+	ch->handlers.debug = empty_fcall_info_cache;
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 	ch->handlers.prereq = empty_fcall_info_cache;
 #endif
@@ -1269,6 +1302,7 @@ void _php_setup_easy_copy_handlers(php_curl *ch, php_curl *source)
 	php_curl_copy_fcc_with_option(ch, CURLOPT_PROGRESSDATA, &ch->handlers.progress, &source->handlers.progress);
 	php_curl_copy_fcc_with_option(ch, CURLOPT_XFERINFODATA, &ch->handlers.xferinfo, &source->handlers.xferinfo);
 	php_curl_copy_fcc_with_option(ch, CURLOPT_FNMATCH_DATA, &ch->handlers.fnmatch, &source->handlers.fnmatch);
+	php_curl_copy_fcc_with_option(ch, CURLOPT_DEBUGDATA, &ch->handlers.debug, &source->handlers.debug);
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 	php_curl_copy_fcc_with_option(ch, CURLOPT_PREREQDATA, &ch->handlers.prereq, &source->handlers.prereq);
 #endif
@@ -1632,6 +1666,8 @@ static zend_result _php_curl_setopt(php_curl *ch, zend_long option, zval *zvalue
 		HANDLE_CURL_OPTION_CALLABLE(ch, CURLOPT_PROGRESS, handlers.progress, curl_progress);
 		HANDLE_CURL_OPTION_CALLABLE(ch, CURLOPT_XFERINFO, handlers.xferinfo, curl_xferinfo);
 		HANDLE_CURL_OPTION_CALLABLE(ch, CURLOPT_FNMATCH_, handlers.fnmatch, curl_fnmatch);
+		HANDLE_CURL_OPTION_CALLABLE(ch, CURLOPT_DEBUG, handlers.debug, curl_debug);
+
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 		HANDLE_CURL_OPTION_CALLABLE(ch, CURLOPT_PREREQ, handlers.prereq, curl_prereqfunction);
 #endif
@@ -2216,6 +2252,11 @@ static zend_result _php_curl_setopt(php_curl *ch, zend_long option, zval *zvalue
 		}
 
 		case CURLINFO_HEADER_OUT:
+			if (ZEND_FCC_INITIALIZED(ch->handlers.debug)) {
+                zend_value_error("CURLINFO_HEADER_OUT option must not be set when the CURLOPT_DEBUGFUNCTION option is set");
+                return FAILURE;
+            }
+
 			if (zend_is_true(zvalue)) {
 				curl_easy_setopt(ch->cp, CURLOPT_DEBUGFUNCTION, curl_debug);
 				curl_easy_setopt(ch->cp, CURLOPT_DEBUGDATA, (void *)ch);
@@ -2795,6 +2836,9 @@ static void curl_free_obj(zend_object *object)
 	if (ZEND_FCC_INITIALIZED(ch->handlers.fnmatch)) {
 		zend_fcc_dtor(&ch->handlers.fnmatch);
 	}
+	if (ZEND_FCC_INITIALIZED(ch->handlers.debug)) {
+		zend_fcc_dtor(&ch->handlers.debug);
+	}
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 	if (ZEND_FCC_INITIALIZED(ch->handlers.prereq)) {
 		zend_fcc_dtor(&ch->handlers.prereq);
@@ -2878,6 +2922,10 @@ static void _php_curl_reset_handlers(php_curl *ch)
 	if (ZEND_FCC_INITIALIZED(ch->handlers.fnmatch)) {
 		zend_fcc_dtor(&ch->handlers.fnmatch);
 	}
+
+	if (ZEND_FCC_INITIALIZED(ch->handlers.debug)) {
+		zend_fcc_dtor(&ch->handlers.debug);
+	}
 #if LIBCURL_VERSION_NUM >= 0x075000 /* Available since 7.80.0 */
 	if (ZEND_FCC_INITIALIZED(ch->handlers.prereq)) {
 		zend_fcc_dtor(&ch->handlers.prereq);
diff --git a/ext/curl/sync-constants.php b/ext/curl/sync-constants.php
index 8f35f7b05fa38..87868bb5b31d9 100755
--- a/ext/curl/sync-constants.php
+++ b/ext/curl/sync-constants.php
@@ -18,6 +18,7 @@
     'CURLOPT_PROGRESSDATA',
     'CURLOPT_XFERINFODATA',
     'CURLOPT_PREREQDATA',
+    'CURLOPT_DEBUGDATA',
 ];
 
 const IGNORED_PHP_CONSTANTS = [
diff --git a/ext/curl/tests/bug48203_multi.phpt b/ext/curl/tests/bug48203_multi.phpt
index ed58f8540d9ef..ec9748517ab85 100644
--- a/ext/curl/tests/bug48203_multi.phpt
+++ b/ext/curl/tests/bug48203_multi.phpt
@@ -4,8 +4,9 @@ Variation of bug #48203 with curl_multi_exec (Crash when file pointers passed to
 curl
 --SKIPIF--
 <?php
-if (getenv("GITHUB_ACTIONS") && PHP_OS_FAMILY === "Darwin" && php_uname("m") === "x86_64") {
-    die("xfail Test fails for unknown reasons");
+if (curl_version()['version_number'] === 0x080a00) {
+    // https://github.com/php/php-src/issues/15997
+    die('xfail due to a libcurl bug');
 }
 ?>
 --FILE--
diff --git a/ext/curl/tests/bug71523.phpt b/ext/curl/tests/bug71523.phpt
index fa32ecdccd596..2cf2477409dae 100644
--- a/ext/curl/tests/bug71523.phpt
+++ b/ext/curl/tests/bug71523.phpt
@@ -4,8 +4,9 @@ Bug #71523 (Copied handle with new option CURLOPT_HTTPHEADER crashes while curl_
 curl
 --SKIPIF--
 <?php
-if (getenv("GITHUB_ACTIONS") && PHP_OS_FAMILY === "Darwin" && php_uname("m") === "x86_64") {
-    die("xfail Test fails for unknown reasons");
+if (curl_version()['version_number'] === 0x080a00) {
+    // https://github.com/php/php-src/issues/15997
+    die('xfail due to a libcurl bug');
 }
 ?>
 --FILE--
diff --git a/ext/curl/tests/curl_basic_018.phpt b/ext/curl/tests/curl_basic_018.phpt
index 72778c82e9ad2..1c907a05fb092 100644
--- a/ext/curl/tests/curl_basic_018.phpt
+++ b/ext/curl/tests/curl_basic_018.phpt
@@ -6,8 +6,9 @@ TestFest 2009 - AFUP - Thomas Rabaix <thomas.rabaix@gmail.com>
 curl
 --SKIPIF--
 <?php
-if (getenv("GITHUB_ACTIONS") && PHP_OS_FAMILY === "Darwin" && php_uname("m") === "x86_64") {
-    die("xfail Test fails for unknown reasons");
+if (curl_version()['version_number'] === 0x080a00) {
+    // https://github.com/php/php-src/issues/15997
+    die('xfail due to a libcurl bug');
 }
 ?>
 --FILE--
diff --git a/ext/curl/tests/curl_multi_getcontent_basic3.phpt b/ext/curl/tests/curl_multi_getcontent_basic3.phpt
index 558440bfe20e5..79002a56430d2 100644
--- a/ext/curl/tests/curl_multi_getcontent_basic3.phpt
+++ b/ext/curl/tests/curl_multi_getcontent_basic3.phpt
@@ -7,8 +7,9 @@ Rein Velt (rein@velt.org)
 curl
 --SKIPIF--
 <?php
-if (getenv("GITHUB_ACTIONS") && PHP_OS_FAMILY === "Darwin" && php_uname("m") === "x86_64") {
-    die("xfail Test fails for unknown reasons");
+if (curl_version()['version_number'] === 0x080a00) {
+    // https://github.com/php/php-src/issues/15997
+    die('xfail due to a libcurl bug');
 }
 ?>
 --FILE--
diff --git a/ext/curl/tests/curl_setopt_CURLOPT_DEBUGFUNCTION.phpt b/ext/curl/tests/curl_setopt_CURLOPT_DEBUGFUNCTION.phpt
new file mode 100644
index 0000000000000..7193642dcab04
--- /dev/null
+++ b/ext/curl/tests/curl_setopt_CURLOPT_DEBUGFUNCTION.phpt
@@ -0,0 +1,236 @@
+--TEST--
+Curl option CURLOPT_DEBUGFUNCTION
+--EXTENSIONS--
+curl
+--FILE--
+<?php
+include 'server.inc';
+
+$allowedTypes = [
+    CURLINFO_TEXT,
+    CURLINFO_HEADER_IN,
+    CURLINFO_HEADER_OUT,
+    CURLINFO_DATA_IN,
+    CURLINFO_DATA_OUT,
+    CURLINFO_SSL_DATA_OUT,
+    CURLINFO_SSL_DATA_IN,
+];
+
+var_dump(CURLOPT_DEBUGFUNCTION);
+
+$host = curl_cli_server_start();
+
+echo "\n===Testing with regular CURLOPT_VERBOSE with verbose=false===\n";
+$ch = curl_init();
+curl_setopt($ch, CURLOPT_URL, "{$host}/get.inc?test=file");
+curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
+curl_setopt($ch, CURLOPT_VERBOSE, 0);
+var_dump(curl_setopt($ch, CURLOPT_DEBUGFUNCTION, function() {
+    echo 'This should not be called';
+}));
+curl_exec($ch);
+curl_setopt($ch, CURLOPT_VERBOSE, 1);
+
+echo "\n===Testing with regular CURLOPT_VERBOSE on stderr===\n";
+$ch = curl_init();
+curl_setopt($ch, CURLOPT_URL, "{$host}/get.inc?test=file");
+curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
+curl_setopt($ch, CURLOPT_VERBOSE, 1);
+$stderr = fopen('php://temp', 'wb+');
+curl_setopt($ch, CURLOPT_STDERR, $stderr);
+$curlVerboseOutput = curl_exec($ch);
+rewind($stderr);
+$receivedOutput = stream_get_contents($stderr);
+fclose($stderr);
+var_dump(str_contains($receivedOutput, 'Host'));
+
+echo "\n===Testing with CURLOPT_DEBUGFUNCTION happy path===\n";
+$stderr = fopen('php://temp', 'wb+');
+curl_setopt($ch, CURLOPT_STDERR, $stderr);
+
+$debugOutput = [];
+var_dump(curl_setopt($ch, CURLOPT_DEBUGFUNCTION, function(CurlHandle $curlHandle, int $type, string $data) use ($allowedTypes, &$debugOutput) {
+    if (!in_array($type, $allowedTypes)) {
+        throw new Exception('Unexpected type value: '. $type);
+    }
+    $debugOutput[$type][] = $data;
+}));
+
+$result = curl_exec($ch);
+rewind($stderr);
+$receivedOutputWithDebugFunction = stream_get_contents($stderr);
+fclose($stderr);
+echo "Received stderr empty:\n";
+var_dump($result);
+var_dump($receivedOutputWithDebugFunction);
+
+// Header-out should be an exact match
+var_dump(str_contains($receivedOutput, $debugOutput[CURLINFO_HEADER_OUT][0]));
+
+// Header-in fields should match, except for the "Date" header that is dynamic.
+foreach ($debugOutput[CURLINFO_HEADER_IN] as $headerReceived) {
+    if (str_starts_with($headerReceived, 'Date')) {
+        continue;
+    }
+    if (!str_contains($receivedOutput, $headerReceived)) {
+        throw new \Exception('DEBUGFUNCTION header field does not match the previous verbose debug message');
+    }
+}
+
+echo "\n===Test attempting to set CURLINFO_HEADER_OUT while CURLOPT_DEBUGFUNCTION in effect throws===\n";
+$ch = curl_init();
+var_dump(curl_setopt($ch, CURLINFO_HEADER_OUT, true));
+var_dump(curl_setopt($ch, CURLOPT_DEBUGFUNCTION, null));
+var_dump(curl_setopt($ch, CURLINFO_HEADER_OUT, true));
+var_dump(curl_setopt($ch, CURLOPT_DEBUGFUNCTION, 'strlen'));
+try {
+    var_dump(curl_setopt($ch, CURLINFO_HEADER_OUT, true));
+}
+catch (\ValueError $e) {
+    var_dump($e->getMessage());
+}
+$chCopy = curl_copy_handle($ch);
+try {
+    var_dump(curl_setopt($chCopy, CURLINFO_HEADER_OUT, true));
+}
+catch (\ValueError $e) {
+    var_dump($e->getMessage());
+}
+var_dump(curl_setopt($chCopy, CURLOPT_DEBUGFUNCTION, null));
+var_dump(curl_setopt($chCopy, CURLINFO_HEADER_OUT, true));
+
+echo "\n===Test attempting to set CURLOPT_DEBUGFUNCTION while CURLINFO_HEADER_OUT does not throw===\n";
+$ch = curl_init();
+var_dump(curl_setopt($ch, CURLINFO_HEADER_OUT, true));
+var_dump(curl_setopt($ch, CURLOPT_DEBUGFUNCTION, null));
+var_dump(curl_setopt($ch, CURLINFO_HEADER_OUT, true));
+var_dump(curl_setopt($ch, CURLOPT_DEBUGFUNCTION, 'strlen'));
+$chCopy = curl_copy_handle($ch);
+var_dump(curl_setopt($ch, CURLOPT_DEBUGFUNCTION, 'strlen'));
+var_dump(curl_setopt($chCopy, CURLOPT_DEBUGFUNCTION, null));
+var_dump(curl_setopt($chCopy, CURLINFO_HEADER_OUT, 1));
+
+echo "\n===Test CURLOPT_DEBUGFUNCTION=null works===\n";
+$ch = curl_init("{$host}/get.inc?test=file");
+var_dump(curl_setopt($ch, CURLOPT_DEBUGFUNCTION, null));
+curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
+var_dump(curl_exec($ch));
+
+echo "\n===Test CURLINFO_HEADER_OUT works while CURLOPT_DEBUGFUNCTION in effect===\n";
+$ch = curl_init("{$host}/get.inc?test=file");
+curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
+var_dump(curl_getinfo($ch, CURLINFO_HEADER_OUT));
+var_dump(curl_setopt($ch, CURLINFO_HEADER_OUT, true));
+var_dump(curl_getinfo($ch, CURLINFO_HEADER_OUT));
+var_dump(curl_setopt($ch, CURLOPT_DEBUGFUNCTION, static function() {}));
+var_dump(curl_getinfo($ch, CURLINFO_HEADER_OUT));
+var_dump($result = curl_exec($ch));
+var_dump(curl_getinfo($ch, CURLINFO_HEADER_OUT));
+
+echo "\n===Test CURLOPT_DEBUGFUNCTION can throw within callback===\n";
+$ch = curl_init("{$host}/get.inc?test=file");
+curl_setopt($ch, CURLOPT_DEBUGFUNCTION, static function() {
+    throw new \RuntimeException('This should get caught after verbose=true');
+});
+var_dump(curl_exec($ch));
+curl_setopt($ch, CURLOPT_VERBOSE, true);
+try {
+    var_dump($result = curl_exec($ch));
+}
+catch (\RuntimeException $e) {
+    var_dump($e->getMessage());
+}
+var_dump(curl_getinfo($ch, CURLINFO_HEADER_OUT));
+
+echo "\n===Test CURLOPT_DEBUGFUNCTION on shared handles work===\n";
+$ch = curl_init("{$host}/get.inc?test=file");
+$called = false;
+curl_setopt_array($ch, [
+    CURLOPT_VERBOSE => true,
+    CURLOPT_DEBUGFUNCTION => static function() use (&$called) {
+        $called = true;
+    },
+]);
+var_dump($called);
+curl_exec($ch);
+var_dump($called);
+$called = false;
+$ch2 = curl_copy_handle($ch);
+curl_exec($ch2);
+var_dump($called);
+var_dump(curl_getinfo($ch2, CURLINFO_HEADER_OUT));
+
+echo "\nDone";
+?>
+--EXPECTF--
+int(20094)
+
+===Testing with regular CURLOPT_VERBOSE with verbose=false===
+bool(true)
+
+===Testing with regular CURLOPT_VERBOSE on stderr===
+bool(true)
+
+===Testing with CURLOPT_DEBUGFUNCTION happy path===
+bool(true)
+Received stderr empty:
+string(0) ""
+string(0) ""
+bool(true)
+
+===Test attempting to set CURLINFO_HEADER_OUT while CURLOPT_DEBUGFUNCTION in effect throws===
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+string(87) "CURLINFO_HEADER_OUT option must not be set when the CURLOPT_DEBUGFUNCTION option is set"
+string(87) "CURLINFO_HEADER_OUT option must not be set when the CURLOPT_DEBUGFUNCTION option is set"
+bool(true)
+bool(true)
+
+===Test attempting to set CURLOPT_DEBUGFUNCTION while CURLINFO_HEADER_OUT does not throw===
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+
+===Test CURLOPT_DEBUGFUNCTION=null works===
+bool(true)
+string(0) ""
+
+===Test CURLINFO_HEADER_OUT works while CURLOPT_DEBUGFUNCTION in effect===
+bool(false)
+bool(true)
+bool(false)
+bool(true)
+bool(false)
+string(0) ""
+string(%d) "GET /get.inc?test=file HTTP/%s
+Host: %s:%d
+Accept: */*
+
+"
+
+===Test CURLOPT_DEBUGFUNCTION can throw within callback===
+bool(true)
+string(41) "This should get caught after verbose=true"
+string(%d) "GET /get.inc?test=file HTTP/%s
+Host: %s:%d
+Accept: */*
+
+"
+
+===Test CURLOPT_DEBUGFUNCTION on shared handles work===
+bool(false)
+bool(true)
+bool(true)
+string(71) "GET /get.inc?test=file HTTP/%s
+Host: %s:%d
+Accept: */*
+
+"
+
+Done
diff --git a/ext/dom/attr.c b/ext/dom/attr.c
index 9ad28232f4ed3..dfe3abc1a885c 100644
--- a/ext/dom/attr.c
+++ b/ext/dom/attr.c
@@ -177,7 +177,8 @@ Since: DOM Level 3
 */
 zend_result dom_attr_schema_type_info_read(dom_object *obj, zval *retval)
 {
-	/* TODO */
+	/* This was never implemented, and is dropped from the modern-day DOM spec.
+	 * It only exists in old DOM to preserve BC. */
 	ZVAL_NULL(retval);
 	return SUCCESS;
 }
diff --git a/ext/opcache/jit/zend_jit_ir.c b/ext/opcache/jit/zend_jit_ir.c
index 4b31f2e07ae71..f8a24c18c242a 100644
--- a/ext/opcache/jit/zend_jit_ir.c
+++ b/ext/opcache/jit/zend_jit_ir.c
@@ -13740,7 +13740,9 @@ static int zend_jit_load_this(zend_jit_ctx *jit, uint32_t var)
 
 static int zend_jit_fetch_this(zend_jit_ctx *jit, const zend_op *opline, const zend_op_array *op_array, bool check_only)
 {
-	if (!op_array->scope || (op_array->fn_flags & ZEND_ACC_STATIC)) {
+	if (!op_array->scope ||
+			(op_array->fn_flags & ZEND_ACC_STATIC) ||
+			((op_array->fn_flags & (ZEND_ACC_CLOSURE|ZEND_ACC_IMMUTABLE)) == ZEND_ACC_CLOSURE)) {
 		if (JIT_G(trigger) == ZEND_JIT_ON_HOT_TRACE) {
 			if (!JIT_G(current_frame) ||
 			    !TRACE_FRAME_IS_THIS_CHECKED(JIT_G(current_frame))) {
diff --git a/ext/opcache/tests/jit/gh15973.phpt b/ext/opcache/tests/jit/gh15973.phpt
new file mode 100644
index 0000000000000..42a039cd51c4e
--- /dev/null
+++ b/ext/opcache/tests/jit/gh15973.phpt
@@ -0,0 +1,24 @@
+--TEST--
+GH-15973 (Segmentation fault in JIT mode 1135)
+--EXTENSIONS--
+opcache
+--INI--
+opcache.jit=1215
+opcache.jit_buffer_size=64M
+--FILE--
+<?php
+class Test {
+}
+$appendProp2 = (function() {
+$this->prop[] = 1;
+})->bindTo($test, Test::class);
+$appendProp2();
+?>
+--EXPECTF--
+Warning: Undefined variable $test in %sgh15973.php on line 6
+
+Fatal error: Uncaught Error: Using $this when not in object context in %sgh15973.php:5
+Stack trace:
+#0 %sgh15973.php(7): Test::{closure:%s}()
+#1 {main}
+  thrown in %sgh15973.php on line 5