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- markus@cvs.openbsd.org 2002/07/24 16:11:18 

[hostfile.c hostfile.h sshconnect.c]
     print out all known keys for a host if we get a unknown host key,
     see discussion at http://marc.theaimsgroup.com/?t=101069210100016&r=1&w=4

     the ssharp mitm tool attacks users in a similar way, so i'd like to
     pointed out again:
        A MITM attack is always possible if the ssh client prints:
        The authenticity of host 'bla' can't be established.
     (protocol version 2 with pubkey authentication allows you to detect
     MITM attacks)
This commit is contained in:
Ben Lindstrom 2002-08-01 01:21:56 +00:00
parent 18d2b5d399
commit 3ed6640532
4 changed files with 124 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
ChangeLog
View File

@ -1,3 +1,17 @@
20020731
- (bal) OpenBSD CVS Sync
- markus@cvs.openbsd.org 2002/07/24 16:11:18
[hostfile.c hostfile.h sshconnect.c]
print out all known keys for a host if we get a unknown host key,
see discussion at http://marc.theaimsgroup.com/?t=101069210100016&r=1&w=4
the ssharp mitm tool attacks users in a similar way, so i'd like to
pointed out again:
A MITM attack is always possible if the ssh client prints:
The authenticity of host 'bla' can't be established.
(protocol version 2 with pubkey authentication allows you to detect
MITM attacks)
20020730
- (bal) [uidswap.c] SCO compile correction by gert@greenie.muc.de
@ -1465,4 +1479,4 @@
- (stevesk) entropy.c: typo in debug message
- (djm) ssh-keygen -i needs seeded RNG; report from markus@
$Id: ChangeLog,v 1.2409 2002/07/30 19:32:07 mouring Exp $
$Id: ChangeLog,v 1.2410 2002/08/01 01:21:56 mouring Exp $

44
hostfile.c
View File

@ -36,7 +36,7 @@
*/
#include "includes.h"
RCSID("$OpenBSD: hostfile.c,v 1.29 2001/12/18 10:04:21 jakob Exp $");
RCSID("$OpenBSD: hostfile.c,v 1.30 2002/07/24 16:11:18 markus Exp $");
#include "packet.h"
#include "match.h"
@ -91,11 +91,14 @@ hostfile_check_key(int bits, Key *key, const char *host, const char *filename, i
* in the list of our known hosts. Returns HOST_OK if the host is known and
* has the specified key, HOST_NEW if the host is not known, and HOST_CHANGED
* if the host is known but used to have a different host key.
*
* If no 'key' has been specified and a key of type 'keytype' is known
* for the specified host, then HOST_FOUND is returned.
*/
HostStatus
check_host_in_hostfile(const char *filename, const char *host, Key *key,
Key *found, int *numret)
static HostStatus
check_host_in_hostfile_by_key_or_type(const char *filename,
const char *host, Key *key, int keytype, Key *found, int *numret)
{
FILE *f;
char line[8192];
@ -105,8 +108,7 @@ check_host_in_hostfile(const char *filename, const char *host, Key *key,
HostStatus end_return;
debug3("check_host_in_hostfile: filename %s", filename);
if (key == NULL)
fatal("no key to look up");
/* Open the file containing the list of known hosts. */
f = fopen(filename, "r");
if (!f)
@ -147,12 +149,20 @@ check_host_in_hostfile(const char *filename, const char *host, Key *key,
*/
if (!hostfile_read_key(&cp, &kbits, found))
continue;
if (!hostfile_check_key(kbits, found, host, filename, linenum))
continue;
if (numret != NULL)
*numret = linenum;
if (key == NULL) {
/* we found a key of the requested type */
if (found->type == keytype)
return HOST_FOUND;
continue;
}
if (!hostfile_check_key(kbits, found, host, filename, linenum))
continue;
/* Check if the current key is the same as the given key. */
if (key_equal(key, found)) {
/* Ok, they match. */
@ -177,6 +187,24 @@ check_host_in_hostfile(const char *filename, const char *host, Key *key,
return end_return;
}
HostStatus
check_host_in_hostfile(const char *filename, const char *host, Key *key,
Key *found, int *numret)
{
if (key == NULL)
fatal("no key to look up");
return (check_host_in_hostfile_by_key_or_type(filename, host, key, 0,
found, numret));
}
int
lookup_key_in_hostfile_by_type(const char *filename, const char *host,
int keytype, Key *found, int *numret)
{
return (check_host_in_hostfile_by_key_or_type(filename, host, NULL,
keytype, found, numret) == HOST_FOUND);
}
/*
* Appends an entry to the host file. Returns false if the entry could not
* be appended.

6
hostfile.h
View File

@ -1,4 +1,4 @@
/* $OpenBSD: hostfile.h,v 1.10 2001/12/18 10:04:21 jakob Exp $ */
/* $OpenBSD: hostfile.h,v 1.11 2002/07/24 16:11:18 markus Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
@ -15,12 +15,14 @@
#define HOSTFILE_H
typedef enum {
HOST_OK, HOST_NEW, HOST_CHANGED
HOST_OK, HOST_NEW, HOST_CHANGED, HOST_FOUND,
} HostStatus;
int hostfile_read_key(char **, u_int *, Key *);
HostStatus
check_host_in_hostfile(const char *, const char *, Key *, Key *, int *);
int add_host_to_hostfile(const char *, const char *, Key *);
int
lookup_key_in_hostfile_by_type(const char *, const char *, int , Key *, int *);
#endif

73
sshconnect.c
View File

@ -13,7 +13,7 @@
*/
#include "includes.h"
RCSID("$OpenBSD: sshconnect.c,v 1.131 2002/07/12 13:29:09 itojun Exp $");
RCSID("$OpenBSD: sshconnect.c,v 1.132 2002/07/24 16:11:18 markus Exp $");
#include <openssl/bn.h>
@ -46,6 +46,8 @@ extern uid_t original_effective_uid;
#define INET6_ADDRSTRLEN 46
#endif
static int show_other_keys(const char *, Key *);
/*
* Connect to the given ssh server using a proxy command.
*/
@ -494,7 +496,7 @@ check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
int salen;
char ntop[NI_MAXHOST];
char msg[1024];
int len, host_line, ip_line;
int len, host_line, ip_line, has_keys;
const char *host_file = NULL, *ip_file = NULL;
/*
@ -638,14 +640,19 @@ check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
"have requested strict checking.", type, host);
goto fail;
} else if (options.strict_host_key_checking == 2) {
has_keys = show_other_keys(host, host_key);
/* The default */
fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
snprintf(msg, sizeof(msg),
"The authenticity of host '%.200s (%s)' can't be "
"established.\n"
"established%s\n"
"%s key fingerprint is %s.\n"
"Are you sure you want to continue connecting "
"(yes/no)? ", host, ip, type, fp);
"(yes/no)? ",
host, ip,
has_keys ? ",\nbut keys of different type are already "
"known for this host." : ".",
type, fp);
xfree(fp);
if (!confirm(msg))
goto fail;
@ -748,6 +755,9 @@ check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
* accept the authentication.
*/
break;
case HOST_FOUND:
fatal("internal error");
break;
}
if (options.check_host_ip && host_status != HOST_CHANGED &&
@ -859,3 +869,58 @@ ssh_put_password(char *password)
memset(padded, 0, size);
xfree(padded);
}
static int
show_key_from_file(const char *file, const char *host, int keytype)
{
Key *found;
char *fp;
int line, ret;
found = key_new(keytype);
if ((ret = lookup_key_in_hostfile_by_type(file, host,
keytype, found, &line))) {
fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
log("WARNING: %s key found for host %s\n"
"in file %s line %d with\n"
"%s key fingerprint %s.",
key_type(found), host, file, line,
key_type(found), fp);
xfree(fp);
}
key_free(found);
return (ret);
}
/* print all known host keys for a given host, but skip keys of given type */
static int
show_other_keys(const char *host, Key *key)
{
int type[] = { KEY_RSA1, KEY_RSA, KEY_DSA, -1};
int i, found = 0;
for (i = 0; type[i] != -1; i++) {
if (type[i] == key->type)
continue;
if (type[i] != KEY_RSA1 &&
show_key_from_file(options.user_hostfile2, host, type[i])) {
found = 1;
continue;
}
if (type[i] != KEY_RSA1 &&
show_key_from_file(options.system_hostfile2, host, type[i])) {
found = 1;
continue;
}
if (show_key_from_file(options.user_hostfile, host, type[i])) {
found = 1;
continue;
}
if (show_key_from_file(options.system_hostfile, host, type[i])) {
found = 1;
continue;
}
debug2("no key of type %d for host %s", type[i], host);
}
return (found);
}