9 files changed, 109 insertions, 55 deletions

diff --git a/ChangeLog b/ChangeLog
index d33de38a7..7b5123412 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+20131231
+ - (djm) OpenBSD CVS Sync
+   - djm@cvs.openbsd.org 2013/12/30 23:52:28
+     [auth2-hostbased.c auth2-pubkey.c compat.c compat.h ssh-rsa.c]
+     [sshconnect.c sshconnect2.c sshd.c]
+     refuse RSA keys from old proprietary clients/servers that use the
+     obsolete RSA+MD5 signature scheme. it will still be possible to connect
+     with these clients/servers but only DSA keys will be accepted, and we'll
+     deprecate them entirely in a future release. ok markus@
+
 20131229
  - (djm) [loginrec.c] Check for username truncation when looking up lastlog
    entries
diff --git a/auth2-hostbased.c b/auth2-hostbased.c
index a344dcc1f..488008f62 100644
--- a/auth2-hostbased.c
+++ b/auth2-hostbased.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-hostbased.c,v 1.16 2013/06/21 00:34:49 djm Exp $ */
+/* $OpenBSD: auth2-hostbased.c,v 1.17 2013/12/30 23:52:27 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -100,6 +100,12 @@ userauth_hostbased(Authctxt *authctxt)
                     "(received %d, expected %d)", key->type, pktype);
                 goto done;
         }
+        if (key_type_plain(key->type) == KEY_RSA &&
+            (datafellows & SSH_BUG_RSASIGMD5) != 0) {
+                error("Refusing RSA key because peer uses unsafe "
+                    "signature format");
+                goto done;
+        }
         service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
             authctxt->service;
         buffer_init(&b);
diff --git a/auth2-pubkey.c b/auth2-pubkey.c
index 2b3ecb104..0fd27bb92 100644
--- a/auth2-pubkey.c
+++ b/auth2-pubkey.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-pubkey.c,v 1.38 2013/06/21 00:34:49 djm Exp $ */
+/* $OpenBSD: auth2-pubkey.c,v 1.39 2013/12/30 23:52:27 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -116,6 +116,12 @@ userauth_pubkey(Authctxt *authctxt)
                     "(received %d, expected %d)", key->type, pktype);
                 goto done;
         }
+        if (key_type_plain(key->type) == KEY_RSA &&
+            (datafellows & SSH_BUG_RSASIGMD5) != 0) {
+                logit("Refusing RSA key because client uses unsafe "
+                    "signature scheme");
+                goto done;
+        }
         if (have_sig) {
                 sig = packet_get_string(&slen);
                 packet_check_eom();
diff --git a/compat.c b/compat.c
index ac353a706..9d9fabef3 100644
--- a/compat.c
+++ b/compat.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: compat.c,v 1.81 2013/05/17 00:13:13 djm Exp $ */
+/* $OpenBSD: compat.c,v 1.82 2013/12/30 23:52:27 djm Exp $ */
 /*
  * Copyright (c) 1999, 2000, 2001, 2002 Markus Friedl.  All rights reserved.
  *
@@ -171,8 +171,9 @@ compat_datafellows(const char *version)
         for (i = 0; check[i].pat; i++) {
                 if (match_pattern_list(version, check[i].pat,
                     strlen(check[i].pat), 0) == 1) {
-                        debug("match: %s pat %s", version, check[i].pat);
                         datafellows = check[i].bugs;
+                        debug("match: %s pat %s compat 0x%08x",
+                            version, check[i].pat, datafellows);
                         return;
                 }
         }
@@ -208,33 +209,59 @@ proto_spec(const char *spec)
         return ret;
 }
 
-char *
-compat_cipher_proposal(char *cipher_prop)
+/*
+ * Filters a proposal string, excluding any algorithm matching the 'filter'
+ * pattern list.
+ */
+static char *
+filter_proposal(char *proposal, const char *filter)
 {
         Buffer b;
-        char *orig_prop, *fix_ciphers;
+        char *orig_prop, *fix_prop;
         char *cp, *tmp;
 
-        if (!(datafellows & SSH_BUG_BIGENDIANAES))
-                return(cipher_prop);
-
         buffer_init(&b);
-        tmp = orig_prop = xstrdup(cipher_prop);
+        tmp = orig_prop = xstrdup(proposal);
         while ((cp = strsep(&tmp, ",")) != NULL) {
-                if (strncmp(cp, "aes", 3) != 0) {
+                if (match_pattern_list(cp, filter, strlen(cp), 0) != 1) {
                         if (buffer_len(&b) > 0)
                                 buffer_append(&b, ",", 1);
                         buffer_append(&b, cp, strlen(cp));
-                }
+                } else
+                        debug2("Compat: skipping algorithm \"%s\"", cp);
         }
         buffer_append(&b, "\0", 1);
-        fix_ciphers = xstrdup(buffer_ptr(&b));
+        fix_prop = xstrdup(buffer_ptr(&b));
         buffer_free(&b);
         free(orig_prop);
-        debug2("Original cipher proposal: %s", cipher_prop);
-        debug2("Compat cipher proposal: %s", fix_ciphers);
-        if (!*fix_ciphers)
-                fatal("No available ciphers found.");
 
-        return(fix_ciphers);
+        return fix_prop;
 }
+
+char *
+compat_cipher_proposal(char *cipher_prop)
+{
+        if (!(datafellows & SSH_BUG_BIGENDIANAES))
+                return cipher_prop;
+        debug2("%s: original cipher proposal: %s", __func__, cipher_prop);
+        cipher_prop = filter_proposal(cipher_prop, "aes*");
+        debug2("%s: compat cipher proposal: %s", __func__, cipher_prop);
+        if (*cipher_prop == '\0')
+                fatal("No supported ciphers found");
+        return cipher_prop;
+}
+
+
+char *
+compat_pkalg_proposal(char *pkalg_prop)
+{
+        if (!(datafellows & SSH_BUG_RSASIGMD5))
+                return pkalg_prop;
+        debug2("%s: original public key proposal: %s", __func__, pkalg_prop);
+        pkalg_prop = filter_proposal(pkalg_prop, "ssh-rsa");
+        debug2("%s: compat public key proposal: %s", __func__, pkalg_prop);
+        if (*pkalg_prop == '\0')
+                fatal("No supported PK algorithms found");
+        return pkalg_prop;
+}
+
diff --git a/compat.h b/compat.h
index 3ae5d9c78..b174fa171 100644
--- a/compat.h
+++ b/compat.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: compat.h,v 1.43 2011/09/23 07:45:05 markus Exp $ */
+/* $OpenBSD: compat.h,v 1.44 2013/12/30 23:52:27 djm Exp $ */
 
 /*
  * Copyright (c) 1999, 2000, 2001 Markus Friedl.  All rights reserved.
@@ -65,6 +65,7 @@ void     enable_compat20(void);
 void     compat_datafellows(const char *);
 int      proto_spec(const char *);
 char    *compat_cipher_proposal(char *);
+char    *compat_pkalg_proposal(char *);
 
 extern int compat13;
 extern int compat20;
diff --git a/ssh-rsa.c b/ssh-rsa.c
index 6e28bb4a6..b1ac50b31 100644
--- a/ssh-rsa.c
+++ b/ssh-rsa.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-rsa.c,v 1.48 2013/12/27 22:37:18 djm Exp $ */
+/* $OpenBSD: ssh-rsa.c,v 1.49 2013/12/30 23:52:27 djm Exp $ */
 /*
  * Copyright (c) 2000, 2003 Markus Friedl <markus@openbsd.org>
  *
@@ -53,7 +53,7 @@ ssh_rsa_sign(const Key *key, u_char **sigp, u_int *lenp,
                 return -1;
         }
 
-        nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
+        nid = NID_sha1;
         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
                 error("%s: EVP_get_digestbynid %d failed", __func__, nid);
                 return -1;
@@ -161,7 +161,7 @@ ssh_rsa_verify(const Key *key, const u_char *signature, u_int signaturelen,
                 memset(sigblob, 0, diff);
                 len = modlen;
         }
-        nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
+        nid = NID_sha1;
         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
                 error("%s: EVP_get_digestbynid %d failed", __func__, nid);
                 free(sigblob);
@@ -196,18 +196,6 @@ static const u_char id_sha1[] = {
         0x05, 0x00, /* NULL */
         0x04, 0x14  /* Octet string, length 0x14 (20), followed by sha1 hash */
 };
-/*
- * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
- *      rsadsi(113549) digestAlgorithm(2) 5 }
- */
-static const u_char id_md5[] = {
-        0x30, 0x20, /* type Sequence, length 0x20 (32) */
-        0x30, 0x0c, /* type Sequence, length 0x0c (12) */
-        0x06, 0x08, /* type OID, length 0x08 */
-        0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */
-        0x05, 0x00, /* NULL */
-        0x04, 0x10  /* Octet string, length 0x10 (16), followed by md5 hash */
-};
 
 static int
 openssh_RSA_verify(int type, u_char *hash, u_int hashlen,
@@ -225,11 +213,6 @@ openssh_RSA_verify(int type, u_char *hash, u_int hashlen,
                 oidlen = sizeof(id_sha1);
                 hlen = 20;
                 break;
-        case NID_md5:
-                oid = id_md5;
-                oidlen = sizeof(id_md5);
-                hlen = 16;
-                break;
         default:
                 goto done;
         }
diff --git a/sshconnect.c b/sshconnect.c
index b492ce915..791b31c12 100644
--- a/sshconnect.c
+++ b/sshconnect.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect.c,v 1.242 2013/12/29 05:57:02 djm Exp $ */
+/* $OpenBSD: sshconnect.c,v 1.243 2013/12/30 23:52:27 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -662,6 +662,9 @@ ssh_exchange_identification(int timeout_ms)
                 fatal("Protocol major versions differ: %d vs. %d",
                     (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
                     remote_major);
+        if ((datafellows & SSH_BUG_RSASIGMD5) != 0)
+                logit("Server version \"%.100s\" uses unsafe RSA signature "
+                    "scheme; disabling use of RSA keys", remote_version);
         if (!client_banner_sent)
                 send_client_banner(connection_out, minor1);
         chop(server_version_string);
diff --git a/sshconnect2.c b/sshconnect2.c
index 1f6160e86..0d339b9c5 100644
--- a/sshconnect2.c
+++ b/sshconnect2.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect2.c,v 1.199 2013/11/02 21:59:15 markus Exp $ */
+/* $OpenBSD: sshconnect2.c,v 1.200 2013/12/30 23:52:28 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Damien Miller.  All rights reserved.
@@ -188,11 +188,12 @@ ssh_kex2(char *host, struct sockaddr *hostaddr, u_short port)
         }
         if (options.hostkeyalgorithms != NULL)
                 myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] =
-                    options.hostkeyalgorithms;
+                    compat_pkalg_proposal(options.hostkeyalgorithms);
         else {
                 /* Prefer algorithms that we already have keys for */
                 myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] =
-                    order_hostkeyalgs(host, hostaddr, port);
+                    compat_pkalg_proposal(
+                    order_hostkeyalgs(host, hostaddr, port));
         }
         if (options.kex_algorithms != NULL)
                 myproposal[PROPOSAL_KEX_ALGS] = options.kex_algorithms;
@@ -1489,17 +1490,31 @@ userauth_pubkey(Authctxt *authctxt)
                  * encrypted keys we cannot do this and have to load the
                  * private key instead
                  */
-                if (id->key && id->key->type != KEY_RSA1) {
-                        debug("Offering %s public key: %s", key_type(id->key),
-                            id->filename);
-                        sent = send_pubkey_test(authctxt, id);
-                } else if (id->key == NULL) {
+                if (id->key != NULL) {
+                        if (key_type_plain(id->key->type) == KEY_RSA &&
+                            (datafellows & SSH_BUG_RSASIGMD5) != 0) {
+                                debug("Skipped %s key %s for RSA/MD5 server",
+                                    key_type(id->key), id->filename);
+                        } else if (id->key->type != KEY_RSA1) {
+                                debug("Offering %s public key: %s",
+                                    key_type(id->key), id->filename);
+                                sent = send_pubkey_test(authctxt, id);
+                        }
+                } else {
                         debug("Trying private key: %s", id->filename);
                         id->key = load_identity_file(id->filename,
                             id->userprovided);
                         if (id->key != NULL) {
                                 id->isprivate = 1;
-                                sent = sign_and_send_pubkey(authctxt, id);
+                                if (key_type_plain(id->key->type) == KEY_RSA &&
+                                    (datafellows & SSH_BUG_RSASIGMD5) != 0) {
+                                        debug("Skipped %s key %s for RSA/MD5 "
+                                            "server", key_type(id->key),
+                                            id->filename);
+                                } else {
+                                        sent = sign_and_send_pubkey(
+                                            authctxt, id);
+                                }
                                 key_free(id->key);
                                 id->key = NULL;
                         }
diff --git a/sshd.c b/sshd.c
index 786d9ff90..87795bea5 100644
--- a/sshd.c
+++ b/sshd.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshd.c,v 1.412 2013/12/06 13:39:49 markus Exp $ */
+/* $OpenBSD: sshd.c,v 1.413 2013/12/30 23:52:28 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -492,17 +492,19 @@ sshd_exchange_identification(int sock_in, int sock_out)
 
         compat_datafellows(remote_version);
 
-        if (datafellows & SSH_BUG_PROBE) {
+        if ((datafellows & SSH_BUG_PROBE) != 0) {
                 logit("probed from %s with %s.  Don't panic.",
                     get_remote_ipaddr(), client_version_string);
                 cleanup_exit(255);
         }
-
-        if (datafellows & SSH_BUG_SCANNER) {
+        if ((datafellows & SSH_BUG_SCANNER) != 0) {
                 logit("scanned from %s with %s.  Don't panic.",
                     get_remote_ipaddr(), client_version_string);
                 cleanup_exit(255);
         }
+        if ((datafellows & SSH_BUG_RSASIGMD5) != 0)
+                logit("Client version \"%.100s\" uses unsafe RSA signature "
+                    "scheme; disabling use of RSA keys", remote_version);
 
         mismatch = 0;
         switch (remote_major) {
@@ -2446,7 +2448,8 @@ do_ssh2_kex(void)
                 packet_set_rekey_limits((u_int32_t)options.rekey_limit,
                     (time_t)options.rekey_interval);
 
-        myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = list_hostkey_types();
+        myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = compat_pkalg_proposal(
+            list_hostkey_types());
 
         /* start key exchange */
         kex = kex_setup(myproposal);