FILTER_FLAG_HOSTNAME accepts ending hyphen

Description

Hello,

The following code:

<?php

$domains = [
    'a-.bc.com',
    'a.bc-.com',
    'a.bc.com-',
];

foreach ($domains as $domain) {
    echo $domain . PHP_EOL;
    var_dump(filter_var($domain, FILTER_VALIDATE_DOMAIN, FILTER_FLAG_HOSTNAME));
    echo PHP_EOL;
}

Resulted in this output:

a-.bc.com
bool(false)

a.bc-.com
bool(false)

a.bc.com-
string(9) "a.bc.com-"    // <------------ here is the bug

I expected this output instead: a.bc.com- test should return false.
I thought that the ending hyphen is not permitted on domain name (https://datatracker.ietf.org/doc/html/rfc1035#section-2.3.1).

This code is tested here : https://3v4l.org/XbMCV

This bug happens in PHP 8.1.30, PHP 8.2.24 and PHP 8.3.12

PHP Version

PHP 8.3.12

Operating System

@Girgias

It is fixable, e.g. if we re looking for hostname, the last element after . should not be an hyphen. However implementation of these filters might not be necessarily "turing complete" more or less on purpose, let's see what @Girgias thinks.

@derickr

The filter extension is quite old, and I haven't looked much into it. IIRC the original author is @derickr and he might have more of an idea.

 ext/filter/logical_filters.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ext/filter/logical_filters.c b/ext/filter/logical_filters.c
index b875819927..7de2dbb96a 100644
--- a/ext/filter/logical_filters.c
+++ b/ext/filter/logical_filters.c
@@ -542,7 +542,7 @@ static int _php_filter_validate_domain(char * domain, size_t len, zend_long flag
 			/* Reset label length counter */
 			i = 1;
 		} else {
-			if (i > 63 || (hostname && *s != '-' && !isalnum((int)*(unsigned char *)s))) {
+			if (i > 63 || (hostname && (*s != '-' || (*s == '-' && *(s + 1) == '\0')) && !isalnum((int)*(unsigned char *)s))) {
 				return 0;
 			}

Oops, can be simplified:

 ext/filter/logical_filters.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ext/filter/logical_filters.c b/ext/filter/logical_filters.c
index b875819927..81f44dafc3 100644
--- a/ext/filter/logical_filters.c
+++ b/ext/filter/logical_filters.c
@@ -542,7 +542,7 @@ static int _php_filter_validate_domain(char * domain, size_t len, zend_long flag
 			/* Reset label length counter */
 			i = 1;
 		} else {
-			if (i > 63 || (hostname && *s != '-' && !isalnum((int)*(unsigned char *)s))) {
+			if (i > 63 || (hostname && (*s != '-' || *(s + 1) == '\0') && !isalnum((int)*(unsigned char *)s))) {
 				return 0;
 			}

Does it work with examples like e-book.com ?

Yeah, sure. See

php-src/ext/filter/logical_filters.c

Lines 535 to 550 in 65f8857

    
           while (s < e) { 
        
           	if (*s == '.') { 
        
           		/* The first and the last character of a label must be alphanumeric */ 
        
           		if (*(s + 1) == '.' || (hostname && (!isalnum((int)*(unsigned char *)(s - 1)) || !isalnum((int)*(unsigned char *)(s + 1))))) { 
        
           			return 0; 
        
           		} 
        
           		/* Reset label length counter */ 
        
           		i = 1; 
        
           	} else { 
        
           		if (i > 63 || (hostname && *s != '-' && !isalnum((int)*(unsigned char *)s))) { 
        
           			return 0; 
        
           		} 
        
           		i++; 
        
           	}

The if branch is for all labels but the last. The else branch is only for the last label, where it had been overlooked to cater to a hyphen at the end.

Fix phpGH-16523: FILTER_FLAG_HOSTNAME accepts ending hyphen

Fix GH-16523: FILTER_FLAG_HOSTNAME accepts ending hyphen

Merge branch 'PHP-8.2' into PHP-8.3

Merge branch 'PHP-8.3' into PHP-8.4

Merge branch 'PHP-8.4'

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FILTER_FLAG_HOSTNAME accepts ending hyphen #16523

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	while (s < e) {
	if (*s == '.') {
	/* The first and the last character of a label must be alphanumeric */
	if ((s + 1) == '.' \|\| (hostname && (!isalnum((int)(unsigned char )(s - 1)) \|\| !isalnum((int)(unsigned char *)(s + 1))))) {
	return 0;
	}

	/* Reset label length counter */
	i = 1;
	} else {
	if (i > 63 \|\| (hostname && s != '-' && !isalnum((int)(unsigned char *)s))) {
	return 0;
	}

	i++;
	}

FILTER_FLAG_HOSTNAME accepts ending hyphen #16523

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devnexen commented on Oct 21, 2024

Girgias commented on Oct 21, 2024

cmb69 commented on Oct 21, 2024

cmb69 commented on Oct 21, 2024

devnexen commented on Oct 21, 2024

cmb69 commented on Oct 21, 2024

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