Pwn2Own Austin 2021 Cisco RV34x RCE 漏洞链复现
2023-3-7 15:57:46 Author: www.secpulse.com(查看原文) 阅读量:32 收藏

  • 前言

  • 固件解压

  • 漏洞分析

    • CVE-2022-20705 Improper Session Management Vulnerability

    • CVE-2022-20707 Command Injection

  • 参考链接

前言

这个RCE漏洞利用链的实现是由几个逻辑洞的结合而导致的,这几天我花了一些时间复现了一遍,在此记录一下。

固件解压

我下载的是 RV345 v1.0.03.24,从官网下载到压缩包解压之后可以看到它的 rootfs 是 ubi 格式的 img。之前我都是使用 kali里的 binwalk 对其进行解压可以直接得到解压之后的文件系统。但是由于前几天我的虚拟机坏了,不得不进行重装,但是我还没有装 kali。故找了一下提取 ubi 格式的方式。在 github 上有一个项目:https://github.com/nlitsme/ubidump,通过里面的 ubidump.py 可以很轻松地提取出 ubi 格式的文件。命令如下:

python3 ubidump.py -s . 0.ubi

漏洞分析

CVE-2022-20705 Improper Session Management Vulnerability

CVE-2022-20705 Improper Session Management Vulnerability,是由于 nginx 的配置不当导致的。nginx 的配置文件是 /etc/nginx/nginx.conf,如下

user www-data;
worker_processes  4;

error_log /dev/null;

events {
   worker_connections  1024;
}

http {
access_log off;
#error_log /var/log/nginx/error.log  error;

upstream jsonrpc {
server 127.0.0.1:9000;
}

upstream rest {
server 127.0.0.1:8008;
}

# For websocket proxy server
include /var/nginx/conf.d/proxy.websocket.conf;
include /var/nginx/sites-enabled/*;
}

可以发现它又加载了: /var/nginx/conf.d/proxy.websocket.conf 和 /var/nginx/sites-enabled/ ,但是固件解压出来的 rootfs 里的 var 目录有些问题,所以笔者只能根据别人的文章找一下漏洞发生的配置文件。结合 rest.url.conf 和 proxy.conf 来看。

location /api/ {
       proxy_pass http://rest;
       include /var/nginx/conf.d/proxy.conf;
}

location /api/operations/ciscosb-file:file-copy {
proxy_pass http://rest;
include /var/nginx/conf.d/proxy.conf;
proxy_read_timeout 3600;
proxy_send_timeout 3600;
}

location /api/operations/ciscosb-file:form-file-upload {
set $deny 1;

if ($http_authorization != "") {
set $deny "0";
}

if ($deny = "1") {
return 403;
}

upload_pass /form-file-upload;
upload_store /tmp/upload;
upload_store_access user:rw group:rw all:rw;
upload_set_form_field $upload_field_name.name "$upload_file_name";
upload_set_form_field $upload_field_name.content_type "$upload_content_type";
upload_set_form_field $upload_field_name.path "$upload_tmp_path";
upload_aggregate_form_field "$upload_field_name.md5" "$upload_file_md5";
upload_aggregate_form_field "$upload_field_name.size" "$upload_file_size";
upload_pass_form_field "^.*$";
upload_cleanup 400 404 499 500-505;
upload_resumable on;
}

location /restconf/ {
       proxy_pass http://rest;
       include /var/nginx/conf.d/proxy.conf;
}

location /restconf/operations/ciscosb-file:file-copy {
       proxy_pass http://rest;
       include /var/nginx/conf.d/proxy.conf;
       proxy_read_timeout 3600;
       proxy_send_timeout 3600;
}

proxy_http_version 1.1;
proxy_set_header Host $http_host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header Authorization $http_authorization;
proxy_set_header Accept-Encoding "";
proxy_set_header Connection "";
proxy_ssl_session_reuse off;
server_name_in_redirect off;

如果我们请求中 Authorization 不为空,此时 set $deny "0",就可以向下调用 upload 模块。它会在调用 /form-file-upload前,把文件上传到 /tmp/upload 下。并且由于没有设置 level,它的存储格式类似 /tmp/upload/0000000001。至此我们可以实现任意文件上传至 /tmp/upload

我们接着向下分析,可以在 rootfs/etc/nginx/conf.d 下找到 web.upload.conf 如下:

location /form-file-upload {
include uwsgi_params;
proxy_buffering off;
uwsgi_modifier1 9;
uwsgi_pass 127.0.0.1:9003;
uwsgi_read_timeout 3600;
uwsgi_send_timeout 3600;
}

location /upload {
set $deny 1;

       if (-f /tmp/websession/token/$cookie_sessionid) {
               set $deny "0";
       }

       if ($deny = "1") {
               return 403;
       }

upload_pass /form-file-upload;
upload_store /tmp/upload;
upload_store_access user:rw group:rw all:rw;
upload_set_form_field $upload_field_name.name "$upload_file_name";
upload_set_form_field $upload_field_name.content_type "$upload_content_type";
upload_set_form_field $upload_field_name.path "$upload_tmp_path";
upload_aggregate_form_field "$upload_field_name.md5" "$upload_file_md5";
upload_aggregate_form_field "$upload_field_name.size" "$upload_file_size";
upload_pass_form_field "^.*$";
upload_cleanup 400 404 499 500-505;
upload_resumable on;
}

我们可以发现其对 /upload 进行了 $cookie_sessionid 的检验,但是并没有对 /form-file-upload 进行检验。我们看一下 /form-file-upload 的后端处理程序。启动脚本 (uwsgi-launcher) 如下:

#!/bin/sh /etc/rc.common

export UWSGI_PLUGIN_DIR=/usr/lib/uwsgi/plugins

start() {
        uwsgi -m --ini /etc/uwsgi/jsonrpc.ini &
        uwsgi -m --ini /etc/uwsgi/blockpage.ini &
        uwsgi -m --ini /etc/uwsgi/upload.ini &
}

stop() {
        killall -9 uwsgi
}

我们再去找一下 /etc/uwsgi/upload.ini

[uwsgi]
plugins = cgi
workers = 1
master = 1
uid = www-data
gid = www-data
socket=127.0.0.1:9003
buffer-size=4096
cgi = /www/cgi-bin/upload.cgi
cgi-allowed-ext = .cgi
cgi-allowed-ext = .pl
cgi-timeout = 300
ignore-sigpipe = true

从上述文件中我们可以知道 /form-file-upload 它对应的后端处理程序是 /www/cgi-bin/upload.cgi。因此我们可以无条件访问 upload.cgi

同时上述配置文件中我们可以看到检查了 /tmp/websession/token/$cookie_sessionid 文件是否存在。但是存在缺陷,就是这里的 $cookie_sessionid 是用户在 http 请求中传进去的一个值,它并没有检查是否存在 ../../ ,也就是说我们可以通过跨目录来导致授权绕过。如:我们可以传递 ../../../etc/firmware_version

同时也可以看到在 upload.cgi 里对 sessionid= 进行了检查,限制了它的字符,但是并没有考虑到传多个 sessionid= 的情况。因为这里的 sessionid= 是遍历 HTTP_COOKIE 并且取出它最后一个 sessionid= 作为实际的 sessionid= 使用,所以我们可以传两个 **sessionid=**。前一个用来绕过 web.upload.conf 里的判断,后一个当作正常的数据用来通过 upload.cgi 的判断。这样也可以实现无条件访问 upload.cgi

我们接着看 upload.cgi

传入适当的参数可以使得我们有能力任意文件移动到 /tmp/www 下,通过这两个漏洞我们也可以伪造出一个 session

CVE-2022-20707 Command Injection

我们继续查看 upload.cgi

这个漏洞可以使得任意命令执行。

参考链接

  • https://bestwing.me/Pwning%20a%20Cisco%20RV340%20%20%E6%BC%8F%E6%B4%9E%E5%88%86%E6%9E%90%EF%BC%88CVE-2022-20705%20%E5%92%8C%20CVE-2022-20707.html

  • https://blog.relyze.com/2022/04/pwning-cisco-rv340-with-4-bug-chain.html

  • https://paper.seebug.org/1890/

  • https://onekey.com/blog/advisory-cisco-rv34x-authentication-bypass-remote-command-execution/

  • https://nosec.org/home/detail/4985.html

本文作者:ChaMd5安全团队

本文为安全脉搏专栏作者发布,转载请注明:https://www.secpulse.com/archives/197154.html


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