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diff -up openssh-8.7p1/compat.c.sshrsacheck openssh-8.7p1/compat.c
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--- openssh-8.7p1/compat.c.sshrsacheck 2023-01-12 13:29:06.338710923 +0100
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+++ openssh-8.7p1/compat.c 2023-01-12 13:29:06.357711165 +0100
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@@ -43,6 +43,7 @@ void
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compat_banner(struct ssh *ssh, const char *version)
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{
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int i;
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+ int forbid_ssh_rsa = 0;
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static struct {
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char *pat;
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int bugs;
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@@ -145,16 +146,21 @@ compat_banner(struct ssh *ssh, const cha
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};
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/* process table, return first match */
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+ forbid_ssh_rsa = (ssh->compat & SSH_RH_RSASIGSHA);
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ssh->compat = 0;
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for (i = 0; check[i].pat; i++) {
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if (match_pattern_list(version, check[i].pat, 0) == 1) {
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debug_f("match: %s pat %s compat 0x%08x",
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version, check[i].pat, check[i].bugs);
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ssh->compat = check[i].bugs;
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+ if (forbid_ssh_rsa)
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+ ssh->compat |= SSH_RH_RSASIGSHA;
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return;
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}
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}
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debug_f("no match: %s", version);
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+ if (forbid_ssh_rsa)
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+ ssh->compat |= SSH_RH_RSASIGSHA;
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}
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/* Always returns pointer to allocated memory, caller must free. */
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diff -up openssh-8.7p1/compat.h.sshrsacheck openssh-8.7p1/compat.h
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--- openssh-8.7p1/compat.h.sshrsacheck 2021-08-20 06:03:49.000000000 +0200
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+++ openssh-8.7p1/compat.h 2023-01-12 13:29:06.358711178 +0100
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@@ -30,7 +30,7 @@
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#define SSH_BUG_UTF8TTYMODE 0x00000001
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#define SSH_BUG_SIGTYPE 0x00000002
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#define SSH_BUG_SIGTYPE74 0x00000004
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-/* #define unused 0x00000008 */
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+#define SSH_RH_RSASIGSHA 0x00000008
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#define SSH_OLD_SESSIONID 0x00000010
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/* #define unused 0x00000020 */
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#define SSH_BUG_DEBUG 0x00000040
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diff -up openssh-8.7p1/serverloop.c.sshrsacheck openssh-8.7p1/serverloop.c
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--- openssh-8.7p1/serverloop.c.sshrsacheck 2023-01-12 14:57:08.118400073 +0100
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+++ openssh-8.7p1/serverloop.c 2023-01-12 14:59:17.330470518 +0100
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@@ -737,6 +737,10 @@ server_input_hostkeys_prove(struct ssh *
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else if (ssh->kex->flags & KEX_RSA_SHA2_256_SUPPORTED)
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sigalg = "rsa-sha2-256";
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}
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+ if (ssh->compat & SSH_RH_RSASIGSHA && sigalg == NULL) {
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+ sigalg = "rsa-sha2-512";
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+ debug3_f("SHA1 signature is not supported, falling back to %s", sigalg);
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+ }
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debug3_f("sign %s key (index %d) using sigalg %s",
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sshkey_type(key), ndx, sigalg == NULL ? "default" : sigalg);
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if ((r = sshbuf_put_cstring(sigbuf,
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diff -up openssh-8.7p1/sshd.c.sshrsacheck openssh-8.7p1/sshd.c
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--- openssh-8.7p1/sshd.c.sshrsacheck 2023-01-12 13:29:06.355711140 +0100
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+++ openssh-8.7p1/sshd.c 2023-01-12 13:29:06.358711178 +0100
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@@ -1640,6 +1651,7 @@ main(int ac, char **av)
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int keytype;
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Authctxt *authctxt;
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struct connection_info *connection_info = NULL;
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+ int forbid_ssh_rsa = 0;
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#ifdef HAVE_SECUREWARE
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(void)set_auth_parameters(ac, av);
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@@ -1938,6 +1950,19 @@ main(int ac, char **av)
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key = NULL;
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continue;
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}
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+ if (key && (sshkey_type_plain(key->type) == KEY_RSA || sshkey_type_plain(key->type) == KEY_RSA_CERT)) {
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+ size_t sign_size = 0;
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+ u_char *tmp = NULL;
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+ u_char data[] = "Test SHA1 vector";
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+ int res;
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+
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+ res = ssh_rsa_sign(key, &tmp, &sign_size, data, sizeof(data), NULL);
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+ free(tmp);
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+ if (res == SSH_ERR_LIBCRYPTO_ERROR) {
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+ logit_f("sshd: ssh-rsa algorithm is disabled");
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+ forbid_ssh_rsa = 1;
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+ }
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+ }
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if (sshkey_is_sk(key) &&
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key->sk_flags & SSH_SK_USER_PRESENCE_REQD) {
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debug("host key %s requires user presence, ignoring",
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2bc7a8 |
@@ -2275,6 +2306,9 @@ main(int ac, char **av)
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2bc7a8 |
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2bc7a8 |
check_ip_options(ssh);
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2bc7a8 |
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+ if (forbid_ssh_rsa)
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+ ssh->compat |= SSH_RH_RSASIGSHA;
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2bc7a8 |
+
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2bc7a8 |
/* Prepare the channels layer */
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2bc7a8 |
channel_init_channels(ssh);
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2bc7a8 |
channel_set_af(ssh, options.address_family);
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