Disable rsh/ssh functionality in imap by default (bug #77153)

Author: smalyshev

NEWS

@@ -17,6 +17,10 @@ PHP                                                                        NEWS
   . Fixed bug #77147 (Fixing 60494 ignored ICONV_MIME_DECODE_CONTINUE_ON_ERROR).
     (cmb)
 
+- IMAP:
+  . Fixed bug #77153 (imap_open allows to run arbitrary shell commands via
+    mailbox parameter). (Stas)
+
 - ODBC:
   . Fixed bug #77079 (odbc_fetch_object has incorrect type signature).
     (Jon Allen)

UPGRADING

@@ -99,6 +99,13 @@ PHP 7.2 UPGRADE NOTES
     from PHP 7.1 on 64-bit machines. This change was necessary to resolve a
     modulo bias bug in the implementation.
 
+- IMAP:
+  Starting with 7.2.13, rsh/ssh logins are disabled by default. Use
+  imap.enable_insecure_rsh if you want to enable them. Note that the IMAP
+  library does not filter mailbox names before passing them to rsh/ssh
+  command, thus passing untrusted data to this function with rsh/ssh enabled
+  is insecure.
+
 ========================================
 2. New Features
 ========================================

ext/imap/php_imap.c

@@ -562,6 +562,15 @@ static const zend_module_dep imap_deps[] = {
 };
 /* }}} */
 
+
+/* {{{ PHP_INI
+ */
+PHP_INI_BEGIN()
+STD_PHP_INI_BOOLEAN("imap.enable_insecure_rsh", "0", PHP_INI_SYSTEM, OnUpdateBool, enable_rsh, zend_imap_globals, imap_globals)
+PHP_INI_END()
+/* }}} */
+
+
 /* {{{ imap_module_entry
  */
 zend_module_entry imap_module_entry = {
@@ -832,6 +841,8 @@ PHP_MINIT_FUNCTION(imap)
 {
 	unsigned long sa_all =	SA_MESSAGES | SA_RECENT | SA_UNSEEN | SA_UIDNEXT | SA_UIDVALIDITY;
 
+	REGISTER_INI_ENTRIES();
+
 #ifndef PHP_WIN32
 	mail_link(&unixdriver);		/* link in the unix driver */
 	mail_link(&mhdriver);		/* link in the mh driver */
@@ -1049,6 +1060,12 @@ PHP_MINIT_FUNCTION(imap)
 	GC_TEXTS               texts
 	*/
 
+	if (!IMAPG(enable_rsh)) {
+		/* disable SSH and RSH, see https://bugs.php.net/bug.php?id=77153 */
+		mail_parameters (NIL, SET_RSHTIMEOUT, 0);
+		mail_parameters (NIL, SET_SSHTIMEOUT, 0);
+	}
+
 	le_imap = zend_register_list_destructors_ex(mail_close_it, NULL, "imap", module_number);
 	return SUCCESS;
 }

ext/imap/php_imap.h

@@ -231,6 +231,7 @@ ZEND_BEGIN_MODULE_GLOBALS(imap)
 #endif
 	/* php_stream for php_mail_gets() */
 	php_stream *gets_stream;
+	zend_bool enable_rsh;
 ZEND_END_MODULE_GLOBALS(imap)
 
 #ifdef ZTS

ext/imap/tests/bug77153.phpt

@@ -0,0 +1,24 @@
+--TEST--                                 
+Bug #77153 (imap_open allows to run arbitrary shell commands via mailbox parameter)
+--SKIPIF--
+<?php
+        if (!extension_loaded("imap")) { 
+                die("skip imap extension not available");  
+        }
+?>
+--FILE--
+<?php
+$payload = "echo 'BUG'> " . __DIR__ . '/__bug';
+$payloadb64 = base64_encode($payload);
+$server = "x -oProxyCommand=echo\t$payloadb64|base64\t-d|sh}";
+@imap_open('{'.$server.':143/imap}INBOX', '', '');
+// clean
+imap_errors();
+var_dump(file_exists(__DIR__ . '/__bug'));
+?>
+--EXPECT--
+bool(false)
+--CLEAN--
+<?php
+if(file_exists(__DIR__ . '/__bug')) unlink(__DIR__ . '/__bug');
+?>