/* $OpenBSD: compat.c,v 1.128 2026/03/02 02:40:15 djm Exp $ */
/*
 * Copyright (c) 1999, 2000, 2001, 2002 Markus Friedl.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/types.h>

#include <stdint.h>
#include <stdlib.h>
#include <stdarg.h>

#include "xmalloc.h"
#include "packet.h"
#include "compat.h"
#include "log.h"
#include "match.h"

/* determine bug flags from SSH protocol banner */
void
compat_banner(struct ssh *ssh, const char *version)
{
        int i;
        static struct {
                char    *pat;
                uint32_t bugs;
        } check[] = {
                { "OpenSSH_2.*,"
                  "OpenSSH_3.0*,"
                  "OpenSSH_3.1*",       SSH_BUG_EXTEOF|SSH_OLD_FORWARD_ADDR|
                                        SSH_BUG_SIGTYPE},
                { "OpenSSH_3.*",        SSH_OLD_FORWARD_ADDR|SSH_BUG_SIGTYPE },
                { "Sun_SSH_1.0*",       SSH_BUG_NOREKEY|SSH_BUG_EXTEOF|
                                        SSH_BUG_SIGTYPE},
                { "OpenSSH_2*,"
                  "OpenSSH_3*,"
                  "OpenSSH_4*",         SSH_BUG_SIGTYPE },
                { "OpenSSH_5*",         SSH_NEW_OPENSSH|SSH_BUG_DYNAMIC_RPORT|
                                        SSH_BUG_SIGTYPE},
                { "OpenSSH_6.6.1*",     SSH_NEW_OPENSSH|SSH_BUG_SIGTYPE},
                { "OpenSSH_6.5*,"
                  "OpenSSH_6.6*",       SSH_NEW_OPENSSH|SSH_BUG_CURVE25519PAD|
                                        SSH_BUG_SIGTYPE},
                { "OpenSSH_7.4*",       SSH_NEW_OPENSSH|SSH_BUG_SIGTYPE|
                                        SSH_BUG_SIGTYPE74},
                { "OpenSSH_7.0*,"
                  "OpenSSH_7.1*,"
                  "OpenSSH_7.2*,"
                  "OpenSSH_7.3*,"
                  "OpenSSH_7.5*,"
                  "OpenSSH_7.6*,"
                  "OpenSSH_7.7*",       SSH_NEW_OPENSSH|SSH_BUG_SIGTYPE},
                { "OpenSSH*",           SSH_NEW_OPENSSH },
                { "*MindTerm*",         0 },
                { "3.0.*",              SSH_BUG_DEBUG },
                { "3.0 SecureCRT*",     SSH_OLD_SESSIONID },
                { "1.7 SecureFX*",      SSH_OLD_SESSIONID },
                { "Cisco-1.*",          SSH_BUG_DHGEX_LARGE|
                                        SSH_BUG_HOSTKEYS },
                { "*SSH_Version_Mapper*",
                                        SSH_BUG_SCANNER },
                { "PuTTY_Local:*,"      /* dev versions < Sep 2014 */
                  "PuTTY-Release-0.5*," /* 0.50-0.57, DH-GEX in >=0.52 */
                  "PuTTY_Release_0.5*," /* 0.58-0.59 */
                  "PuTTY_Release_0.60*,"
                  "PuTTY_Release_0.61*,"
                  "PuTTY_Release_0.62*,"
                  "PuTTY_Release_0.63*,"
                  "PuTTY_Release_0.64*",
                                        SSH_OLD_DHGEX },
                { "FuTTY*",             SSH_OLD_DHGEX }, /* Putty Fork */
                { "Probe-*",
                                        SSH_BUG_PROBE },
                { "TeraTerm SSH*,"
                  "TTSSH/1.5.*,"
                  "TTSSH/2.1*,"
                  "TTSSH/2.2*,"
                  "TTSSH/2.3*,"
                  "TTSSH/2.4*,"
                  "TTSSH/2.5*,"
                  "TTSSH/2.6*,"
                  "TTSSH/2.70*,"
                  "TTSSH/2.71*,"
                  "TTSSH/2.72*",        SSH_BUG_HOSTKEYS },
                { "WinSCP_release_4*,"
                  "WinSCP_release_5.0*,"
                  "WinSCP_release_5.1,"
                  "WinSCP_release_5.1.*,"
                  "WinSCP_release_5.5,"
                  "WinSCP_release_5.5.*,"
                  "WinSCP_release_5.6,"
                  "WinSCP_release_5.6.*,"
                  "WinSCP_release_5.7,"
                  "WinSCP_release_5.7.1,"
                  "WinSCP_release_5.7.2,"
                  "WinSCP_release_5.7.3,"
                  "WinSCP_release_5.7.4",
                                        SSH_OLD_DHGEX },
                { "ConfD-*",
                                        SSH_BUG_UTF8TTYMODE },
                { "Twisted_*",          0 },
                { "Twisted*",           SSH_BUG_DEBUG },
                { NULL,                 0 }
        };

        /* process table, return first match */
        ssh->compat = 0;
        for (i = 0; check[i].pat; i++) {
                if (match_pattern_list(version, check[i].pat, 0) == 1) {
                        debug_f("match: %s pat %s compat 0x%08x",
                            version, check[i].pat, check[i].bugs);
                        ssh->compat = check[i].bugs;
                        return;
                }
        }
        debug_f("no match: %s", version);
}

/* Always returns pointer to allocated memory, caller must free. */
char *
compat_kex_proposal(struct ssh *ssh, const char *p)
{
        char *cp = NULL, *cp2 = NULL;

        if ((ssh->compat & (SSH_BUG_CURVE25519PAD|SSH_OLD_DHGEX)) == 0)
                return xstrdup(p);
        debug2_f("original KEX proposal: %s", p);
        if ((ssh->compat & SSH_BUG_CURVE25519PAD) != 0)
                if ((cp = match_filter_denylist(p,
                    "curve25519-sha256@libssh.org")) == NULL)
                        fatal("match_filter_denylist failed");
        if ((ssh->compat & SSH_OLD_DHGEX) != 0) {
                if ((cp2 = match_filter_denylist(cp ? cp : p,
                    "diffie-hellman-group-exchange-sha256,"
                    "diffie-hellman-group-exchange-sha1")) == NULL)
                        fatal("match_filter_denylist failed");
                free(cp);
                cp = cp2;
        }
        if (cp == NULL || *cp == '\0')
                fatal("No supported key exchange algorithms found");
        debug2_f("compat KEX proposal: %s", cp);
        return cp;
}