Linux Fokirtor Backdoor [新的Linux后门]
日前，赛门铁克发布博客称，在五月的一次安全事件中，发现一名黑客入侵了一个大型物联网托管服务商，并且在内部管理系统上使用了一个有意思的Linux后门 – Fokirtor。
经过赛门铁克研究发现，该后门能够伪装它的通信流量，并伪装成正常的SSH通信流量。该后门支持攻击者运行常用的功能，如执行远程命令、反向链接到C&C服务器，Fokirtor能够监控SSH网络流量，如果检测到流量中存在冒号、感叹号、分号、句号（“:!;.”），一旦检测到流量存在这些字符，Fokirtor代码能够解析除这些字符之外的流量，然后提取经过Blowfish和Base64加密的命令。
当服务器感染该后门后，它从机器上收集以下信息：
1、主机名和IP地址
2、端口
3、密码
4、SSH密钥
5、用户名收集之后对信息进行加密，并发送到攻击者的C&C服务器。
赛门铁克分析师表示，要识别网络中是否存在该后门，可以看流量中是否包含了感叹号字符，正常的SSH流量中是不会包含感叹号的。
Linux Fokirtor Backdoor检测脚本
#!/bin/sh
#
# A simple check to see if running ssh processes contain any string that have
# been designated an indication of Fokirtor by Symantec.
#
# More info here:
# http://www.symantec.com/connect/blogs/linux-back-door-uses-covert-communication-protocol
#
# (c) 2013, Kumina bv, [email protected]
#
# You are free to use, modify and distribute this check in any way you see
# fit. Just don't say you wrote it.
#
# This check is created for Debian Squeeze/Wheezy, no idea if it'll work in
# other distros. You'll need gdb-minimal (for gcore) installed.
# We need to be root
if [ `/usr/bin/id -u` -ne 0 ]; then
echo "You need root for this script. Sorry."
exit 1
fi
# For all pids of the ssh process, do the check
for pid in `/bin/pidof sshd`; do
t=$(/bin/mktemp)
/usr/bin/gdb </dev/null --nx --batch \
-ex "set pagination off" -ex "set height 0 " -ex "set width 0" \
-ex "attach $pid" -ex "gcore $t" -ex detach -ex quit
i=0
for str in hbt= key= dhost= sp= sk= dip=; do
/usr/bin/strings $t | /bin/grep "${str}[[:digit:]]"
if [ $? -eq 0 ]; then
i=$(($i + 1))
fi
done
/bin/rm $t
if [ $i -eq 6 ]; then
echo "CRITICAL: Fokirtor strings found in sshd process ${pid}!"
exit 2
fi
done
echo "OK: No indication of Fokirtor found."
exit 0