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Bug #60903 preg_match + operator fails with string exceeding length 18
Submitted: 2012-01-27 15:50 UTC Modified: 2012-01-27 20:56 UTC
From: gohanman at gmail dot com Assigned:
Status: Not a bug Package: PCRE related
PHP Version: 5.3.9 OS: Ubuntu
Private report: No CVE-ID: None
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From: gohanman at gmail dot com
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 [2012-01-27 15:50 UTC] gohanman at gmail dot com 
Description:
------------
I'm trying to validate email addresses via regular expression. My regular expression fails if the first domain portion is longer than 18 characters. Overall string length does not seem relevant. Decreasing the length of the user portion or TLD does not make a 19+ character domain portion work.

Test script:
---------------
function is_email($str){
        if(preg_match("/^[_a-z0-9-]+(.[_a-z0-9-]+)*@[a-z0-9-]+(.[a-z0-9-]+)*(.[a-z]{2,4})$/i", $str))
                return True;
        return False;
}

var_dump(is_email("user@123456789012345678.com"));
var_dump(is_email("user@1234567890123456789.com"));

Expected result:
----------------
bool(true);
bool(true);

Actual result:
--------------
bool(true);
bool(false);

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 [2012-01-27 20:54 UTC] felipe@php.net 
Are you really using 5.3.9 with the built-in PCRE library?
Your test case works just fine here.

If it returns false, you can check preg_last_error() and adjust the INI configuration accordingly. About crashing, it's known behavior from PCRE library, take a look at the PCRE documentation for more information.
 [2012-01-27 20:54 UTC] felipe@php.net
-Status: Open +Status: Not a bug -Package: Regexps related +Package: PCRE related
 [2012-01-27 20:56 UTC] nikic@php.net 
This is not a PHP bug. Your regex is written somewhat inefficiently (and doesn't do what you expect it to) and thus seems to quickly hit the backtracking limit. Btw, I can't repro it on 5.3, only 5.2.

What you actually wanted to write is /^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,4})$/i (not the \.).

By the way, we encourage you to use filter_var with FILTER_VALIDATE_EMAIL instead of a custom regex. Custom solutions usually are much too restrictive and disallow many valid emails.
 [2012-01-27 20:56 UTC] nikic@php.net
-Package: PCRE related +Package: Regexps related
 [2012-01-27 20:56 UTC] nikic@php.net
-Package: Regexps related +Package: PCRE related
 
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