0x01 前言

今日【CVE 2015-0235: GNU glibc gethostbyname 缓冲区溢出漏洞 】全面爆发，该漏洞的产生是Qualys公司在进行内部代码审核时，发现了一个在GNU C库(glibc)中存在的__nss_hostname_digits_dots函数导致的缓冲区溢出漏洞。这个bug可以通过gethostbyname *()函数来触发，本地和远程均可行。该漏洞（幽灵漏洞）造成了远程代码执行，攻击者可以利用此漏洞远程获取系统进程当前的权限。

鉴于网上诸多glibc的原理普及，本文章就不多啰嗦了，直接实践如何检测服务器是否存在该漏洞，以及修复漏洞的方法。

0x02 检测是否存在该漏洞

检测方法1【RedHat官方检测方法】：

ghost_check.sh源码:

#!/bin/bash
vercomp () {
if [[ $1 == $2 ]]
then
return 0
fi
local IFS=.
local i ver1=($1) ver2=($2)
    # fill empty fields in ver1 with zeros
    for ((i=${#ver1[@]}; i<${#ver2[@]}; i++))
do
ver1[i]=0
done
    for ((i=0; i<${#ver1[@]}; i++))
do
if [[ -z ${ver2[i]} ]]
then
            # fill empty fields in ver2 with zeros
ver2[i]=0
fi
        if ((10#${ver1[i]} > 10#${ver2[i]}))
then
return 1
fi
        if ((10#${ver1[i]} < 10#${ver2[i]}))
then
return 2
fi
done
return 0
}

glibc_vulnerable_version=2.17
glibc_vulnerable_revision=54
glibc_vulnerable_version2=2.5
glibc_vulnerable_revision2=122
glibc_vulnerable_version3=2.12
glibc_vulnerable_revision3=148
echo "Vulnerable glibc version <=" $glibc_vulnerable_version"-"$glibc_vulnerable_revision
echo "Vulnerable glibc version <=" $glibc_vulnerable_version2"-"$glibc_vulnerable_revision2
echo "Vulnerable glibc version <=" $glibc_vulnerable_version3"-1."$glibc_vulnerable_revision3

glibc_version=$(rpm -q glibc | awk -F"[-.]" '{print $2"."$3}' | sort -u)
if [[ $glibc_version == $glibc_vulnerable_version3 ]]
then
glibc_revision=$(rpm -q glibc | awk -F"[-.]" '{print $5}' | sort -u)
else
glibc_revision=$(rpm -q glibc | awk -F"[-.]" '{print $4}' | sort -u)
fi
echo "Detected glibc version" $glibc_version" revision "$glibc_revision

vulnerable_text=$"This system is vulnerable to CVE-2015-0235. <https://access.redhat.com/security/cve/CVE-2015-0235>
Update the glibc and ncsd packages on your system using the packages released with the following:
yum install glibc"

if [[ $glibc_version == $glibc_vulnerable_version ]]
then
vercomp $glibc_vulnerable_revision $glibc_revision
elif [[ $glibc_version == $glibc_vulnerable_version2 ]]
then
vercomp $glibc_vulnerable_revision2 $glibc_revision
elif [[ $glibc_version == $glibc_vulnerable_version3 ]]
then
vercomp $glibc_vulnerable_revision3 $glibc_revision
else
vercomp $glibc_vulnerable_version $glibc_version
fi

case $? in
    0) echo "$vulnerable_text";;
    1) echo "$vulnerable_text";;
    2) echo "Not Vulnerable.";;
esac

检测方法2【简单的检测方法】：

检测方法2源码:

/usr/sbin/clockdiff `python -c "print '0' * $((0x10000-16*1-2*4-1-4))"`

检测方法3【二进制检测方法】：

ghost.c源码:

#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#define CANARY "in_the_coal_mine"

struct {
char buffer[1024];
char canary[sizeof(CANARY)];
} temp = { "buffer", CANARY };

int main(void) {
struct hostent resbuf;
struct hostent *result;
int herrno;
int retval;

  /*** strlen (name) = size_needed - sizeof (*host_addr) - sizeof (*h_addr_ptrs) - 1; ***/
size_t len = sizeof(temp.buffer) - 16*sizeof(unsigned char) - 2*sizeof(char *) - 1;
char name[sizeof(temp.buffer)];
memset(name, '0', len);
name[len] = '\0';

retval = gethostbyname_r(name, &resbuf, temp.buffer, sizeof(temp.buffer), &result, &herrno);

if (strcmp(temp.canary, CANARY) != 0) {
    puts("vulnerable");
exit(EXIT_SUCCESS);
}
if (retval == ERANGE) {
    puts("not vulnerable");
exit(EXIT_SUCCESS);
}
  puts("should not happen");
exit(EXIT_FAILURE);
}

0x03 在线修复方案

CentOS, Red Hat, Fedora等系列衍生版本(RHN建议)：

yum update glibc

Debian, Ubuntu等系列衍生版本：

apt-get clean && apt-get update && apt-get upgrade

0x04 离线修复方案

Centos6.5离线补丁

先检查本地glibc包安装了哪些相关包
 

rpm -qa|grep glibc

然后，到阿里源下载对应版本

cat > update.txt << EOF
http://mirrors.aliyun.com/centos/6.6/updates/x86_64/Packages/glibc-2.12-1.149.el6_6.5.i686.rpm
http://mirrors.aliyun.com/centos/6.6/updates/x86_64/Packages/glibc-2.12-1.149.el6_6.5.x86_64.rpm
http://mirrors.aliyun.com/centos/6.6/updates/x86_64/Packages/glibc-common-2.12-1.149.el6_6.5.x86_64.rpm
http://mirrors.aliyun.com/centos/6.6/updates/x86_64/Packages/glibc-devel-2.12-1.149.el6_6.5.x86_64.rpm    
http://mirrors.aliyun.com/centos/6.6/updates/x86_64/Packages/glibc-headers-2.12-1.149.el6_6.5.x86_64.rpm
EOF

进行后台断点下载补丁包

wget -b -i update.txt -c

使用yum本地安装

yum localinstall glibc-*

或是rpm安装

rpm -ivUh glibc-*

Red Had系列衍生版本

使用方法参考上文【Centos6.5离线补丁】的修补方法
http://mirrors.aliyun.com/centos/7/updates/x86_64/Packages/glibc-2.17-55.el7_0.5.i686.rpm
http://mirrors.aliyun.com/centos/7/updates/x86_64/Packages/glibc-2.17-55.el7_0.5.x86_64.rpm

0x05 修复完成检测

ghost_check.sh脚本检测

ghost.c脚本检测

注意：打好补丁后必须立即重启操作系统，否则会造成应用业务无法使用。

0x06 参考来源

redhat官方
https://access.redhat.com/articles/1332213

redhat官方补丁介绍:
https://rhn.redhat.com/errata/RHSA-2015-0090.html
https://rhn.redhat.com/errata/RHSA-2015-0092.html

ubuntu官方补丁介绍:
http://www.ubuntu.com/usn/usn-2485-1/