Backported from 5.6.25 by Remi.

From 61156f0d68704df748b5cbf08c77582c208db8c9 Mon Sep 17 00:00:00 2001
From: Stanislav Malyshev <stas@php.net>
Date: Wed, 3 Aug 2016 00:30:12 -0700
Subject: [PATCH] Fix bug #72681 - consume data even if we're not storing them

---
 ext/session/session.c           | 25 ++++++++++++++++++-------
 ext/session/tests/bug72681.phpt | 16 ++++++++++++++++
 2 files changed, 34 insertions(+), 7 deletions(-)
 create mode 100644 ext/session/tests/bug72681.phpt

diff --git a/ext/session/session.c b/ext/session/session.c
index c668bb7..b2d0236 100644
--- a/ext/session/session.c
+++ b/ext/session/session.c
@@ -923,11 +923,13 @@ PS_SERIALIZER_DECODE_FUNC(php_binary) /* {{{ */
 	int namelen;
 	int has_value;
 	php_unserialize_data_t var_hash;
+	int skip = 0;
 
 	PHP_VAR_UNSERIALIZE_INIT(var_hash);
 
 	for (p = val; p < endptr; ) {
 		zval **tmp;
+		skip = 0;
 		namelen = ((unsigned char)(*p)) & (~PS_BIN_UNDEF);
 
 		if (namelen < 0 || namelen > PS_BIN_MAX || (p + namelen) >= endptr) {
@@ -943,22 +945,25 @@ PS_SERIALIZER_DECODE_FUNC(php_binary) /* {{{ */
 
 		if (zend_hash_find(&EG(symbol_table), name, namelen + 1, (void **) &tmp) == SUCCESS) {
 			if ((Z_TYPE_PP(tmp) == IS_ARRAY && Z_ARRVAL_PP(tmp) == &EG(symbol_table)) || *tmp == PS(http_session_vars)) {
-				efree(name);
-				continue;
+				skip = 1;
 			}
 		}
 
 		if (has_value) {
 			ALLOC_INIT_ZVAL(current);
 			if (php_var_unserialize(&current, (const unsigned char **) &p, (const unsigned char *) endptr, &var_hash TSRMLS_CC)) {
-				php_set_session_var(name, namelen, current, &var_hash  TSRMLS_CC);
+				if (!skip) {
+					php_set_session_var(name, namelen, current, &var_hash  TSRMLS_CC);
+				}
 			} else {
 				PHP_VAR_UNSERIALIZE_DESTROY(var_hash);
 				return FAILURE;
 			}
 			var_push_dtor_no_addref(&var_hash, &current);
 		}
-		PS_ADD_VARL(name, namelen);
+		if (!skip) {
+			PS_ADD_VARL(name, namelen);
+		}
 		efree(name);
 	}
 
@@ -1015,6 +1020,7 @@ PS_SERIALIZER_DECODE_FUNC(php) /* {{{ */
 	int namelen;
 	int has_value;
 	php_unserialize_data_t var_hash;
+	int skip = 0;
 
 	PHP_VAR_UNSERIALIZE_INIT(var_hash);
 
@@ -1023,6 +1029,7 @@ PS_SERIALIZER_DECODE_FUNC(php) /* {{{ */
 	while (p < endptr) {
 		zval **tmp;
 		q = p;
+		skip = 0;
 		while (*q != PS_DELIMITER) {
 			if (++q >= endptr) goto break_outer_loop;
 		}
@@ -1039,14 +1046,16 @@ PS_SERIALIZER_DECODE_FUNC(php) /* {{{ */
 
 		if (zend_hash_find(&EG(symbol_table), name, namelen + 1, (void **) &tmp) == SUCCESS) {
 			if ((Z_TYPE_PP(tmp) == IS_ARRAY && Z_ARRVAL_PP(tmp) == &EG(symbol_table)) || *tmp == PS(http_session_vars)) {
-				goto skip;
+				skip = 1;
 			}
 		}
 
 		if (has_value) {
 			ALLOC_INIT_ZVAL(current);
 			if (php_var_unserialize(&current, (const unsigned char **) &q, (const unsigned char *) endptr, &var_hash TSRMLS_CC)) {
-				php_set_session_var(name, namelen, current, &var_hash  TSRMLS_CC);
+				if (!skip) {
+					php_set_session_var(name, namelen, current, &var_hash  TSRMLS_CC);
+				}
 			} else {
 				var_push_dtor_no_addref(&var_hash, &current);
 				efree(name);
@@ -1055,7 +1064,9 @@ PS_SERIALIZER_DECODE_FUNC(php) /* {{{ */
 			}
 			var_push_dtor_no_addref(&var_hash, &current);
 		}
-		PS_ADD_VARL(name, namelen);
+		if (!skip) {
+			PS_ADD_VARL(name, namelen);
+		}
 skip:
 		efree(name);
 
diff --git a/ext/session/tests/bug72681.phpt b/ext/session/tests/bug72681.phpt
new file mode 100644
index 0000000..ca38b07
--- /dev/null
+++ b/ext/session/tests/bug72681.phpt
@@ -0,0 +1,16 @@
+--TEST--
+Bug #72681: PHP Session Data Injection Vulnerability
+--SKIPIF--
+<?php include('skipif.inc'); ?>
+--FILE--
+<?php
+ini_set('session.serialize_handler', 'php');
+session_start();
+$_SESSION['_SESSION'] = 'ryat|O:8:"stdClass":0:{}';
+session_write_close();
+session_start();
+var_dump($_SESSION);
+?>
+--EXPECT--
+array(0) {
+}