现在普遍的Nginx + PHP cgi的做法是在配置文件中,　通过正则匹配Nginx(PHP/fastcgi的PATH_INFO问题,设置SCRIPT_FILENAME, 今天发现了一个这种方式的安全漏洞.

为什么会这样呢?

比如, 如下的nginx conf:

location ~ .php($|/) {

fastcgi_pass 127.0.0.1:9000;

fastcgi_index index.php;

set $script $uri;

set $path_info "";

if ($uri ~ "^(.+\.php)(/.*)") {

set $script $1;

set $path_info $2;

}

include fastcgi_params;

fastcgi_param SCRIPT_FILENAME $document_root$script;

fastcgi_param SCRIPT_NAME $script;

fastcgi_param PATH_INFO $path_info;

}

通过正则匹配以后, SCRIPT_NAME会被设置为”fake.jpg/foo.php”, 继而构造成SCRIPT_FILENAME传递个PHP CGI, 但是PHP又为什么会接受这样的参数, 并且把a.jpg解析呢?

这就要说到PHP的cgi SAPI中的参数, fix_pathinfo了:

; cgi.fix_pathinfo provides real PATH_INFO/PATH_TRANSLATED support for CGI. PHP's

; previous behaviour was to set PATH_TRANSLATED to SCRIPT_FILENAME, and to not grok

; what PATH_INFO is. For more information on PATH_INFO, see the cgi specs. Setting

; this to 1 will cause PHP CGI to fix it's paths to conform to the spec. A setting

; of zero causes PHP to behave as before. Default is 1. You should fix your scripts

; to use SCRIPT_FILENAME rather than PATH_TRANSLATED.

cgi.fix_pathinfo=1

如果开启了这个选项, 那么就会触发在PHP中的如下逻辑:

/*

if the file doesn't exist, try to extract PATH_INFO out

of it by stat'ing back through the '/'

this fixes url's like /info.php/test

*/

if (script_path_translated &&

(script_path_translated_len = strlen(script_path_translated)) > 0 &&

(script_path_translated[script_path_translated_len-1] == '/' ||

....//以下省略.

到这里, PHP会认为SCRIPT_FILENAME是fake.jpg, 而foo.php是PATH_INFO, 然后PHP就把fake.jpg当作一个PHP文件来解释执行… So…

这个隐患的危害用小顿的话来说, 是巨大的.

对于一些论坛来说, 如果上传一个图片(实际上是恶意的PHP脚本), 继而构造这样的访问请求…

所以, 大家如果有用这种服务器搭配的, 请排查, 如果有隐患,

请关闭fix_pathinfo(默认是开启的).

cgi.fix_pathinfo=0