Fix CVE-2018-15473, a method by which remote clients can enumerate usernames on the server: http://seclists.org/oss-sec/2018/q3/124 https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-15473 Patch adapted from upstream source repository: https://anongit.mindrot.org/openssh.git/commit/?id=74287f5df9966a0648b4a68417451dd18f079ab8 From 74287f5df9966a0648b4a68417451dd18f079ab8 Mon Sep 17 00:00:00 2001 From: "djm@openbsd.org" Date: Tue, 31 Jul 2018 03:10:27 +0000 Subject: [PATCH] upstream: delay bailout for invalid authentic =?UTF-8?q?ating=20user=20until=20after=20the=20packet=20containing=20the?= =?UTF-8?q?=20request=20has=20been=20fully=20parsed.=20Reported=20by=20Dar?= =?UTF-8?q?iusz=20Tytko=20and=20Micha=C5=82=20Sajdak;=20ok=20deraadt?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit OpenBSD-Commit-ID: b4891882fbe413f230fe8ac8a37349b03bd0b70d --- auth2-gss.c | 11 +++++++---- auth2-hostbased.c | 11 ++++++----- auth2-pubkey.c | 25 +++++++++++++++---------- 3 files changed, 28 insertions(+), 19 deletions(-) # Adapted from upstream to apply to OpenSSH 7.7p1. diff --git a/auth2-gss.c b/auth2-gss.c index 589283b7..1d7cfb39 100644 --- a/auth2-gss.c +++ b/auth2-gss.c @@ -69,9 +69,6 @@ userauth_gssapi(struct ssh *ssh) u_int len; u_char *doid = NULL; - if (!authctxt->valid || authctxt->user == NULL) - return (0); - mechs = packet_get_int(); if (mechs == 0) { debug("Mechanism negotiation is not supported"); diff --git a/auth2-gss.c b/auth2-gss.c index 47308c5c..9351e042 100644 --- a/auth2-gss.c +++ b/auth2-gss.c @@ -106,6 +103,12 @@ userauth_gssapi(struct ssh *ssh) return (0); } + if (!authctxt->valid || authctxt->user == NULL) { + debug2("%s: disabled because of invalid user", __func__); + free(doid); + return (0); + } + if (GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctxt, &goid)))) { if (ctxt != NULL) ssh_gssapi_delete_ctx(&ctxt); diff --git a/auth2-hostbased.c b/auth2-hostbased.c index 60159a56..35939329 100644 --- a/auth2-hostbased.c +++ b/auth2-hostbased.c @@ -67,10 +67,6 @@ userauth_hostbased(struct ssh *ssh) size_t alen, blen, slen; int r, pktype, authenticated = 0; - if (!authctxt->valid) { - debug2("%s: disabled because of invalid user", __func__); - return 0; - } /* XXX use sshkey_froms() */ if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 || (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 || @@ -117,6 +113,11 @@ userauth_hostbased(struct ssh *ssh) goto done; } + if (!authctxt->valid || authctxt->user == NULL) { + debug2("%s: disabled because of invalid user", __func__); + goto done; + } + if ((b = sshbuf_new()) == NULL) fatal("%s: sshbuf_new failed", __func__); /* reconstruct packet */ diff --git a/auth2-pubkey.c b/auth2-pubkey.c index c4d0f790..e1c15040 100644 --- a/auth2-pubkey.c +++ b/auth2-pubkey.c @@ -89,19 +89,15 @@ userauth_pubkey(struct ssh *ssh) { Authctxt *authctxt = ssh->authctxt; struct passwd *pw = authctxt->pw; - struct sshbuf *b; + struct sshbuf *b = NULL; struct sshkey *key = NULL; - char *pkalg, *userstyle = NULL, *key_s = NULL, *ca_s = NULL; - u_char *pkblob, *sig, have_sig; + char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL; + u_char *pkblob = NULL, *sig = NULL, have_sig; size_t blen, slen; int r, pktype; int authenticated = 0; struct sshauthopt *authopts = NULL; - if (!authctxt->valid) { - debug2("%s: disabled because of invalid user", __func__); - return 0; - } if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 || (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 || (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0) @@ -167,6 +163,11 @@ userauth_pubkey(struct ssh *ssh) fatal("%s: sshbuf_put_string session id: %s", __func__, ssh_err(r)); } + if (!authctxt->valid || authctxt->user == NULL) { + debug2("%s: disabled because of invalid user", + __func__); + goto done; + } /* reconstruct packet */ xasprintf(&userstyle, "%s%s%s", authctxt->user, authctxt->style ? ":" : "", @@ -183,7 +184,6 @@ userauth_pubkey(struct ssh *ssh) #ifdef DEBUG_PK sshbuf_dump(b, stderr); #endif - /* test for correct signature */ authenticated = 0; if (PRIVSEP(user_key_allowed(ssh, pw, key, 1, &authopts)) && @@ -194,7 +194,6 @@ userauth_pubkey(struct ssh *ssh) authenticated = 1; } sshbuf_free(b); - free(sig); auth2_record_key(authctxt, authenticated, key); } else { debug("%s: test pkalg %s pkblob %s%s%s", @@ -205,6 +204,11 @@ userauth_pubkey(struct ssh *ssh) if ((r = sshpkt_get_end(ssh)) != 0) fatal("%s: %s", __func__, ssh_err(r)); + if (!authctxt->valid || authctxt->user == NULL) { + debug2("%s: disabled because of invalid user", + __func__); + goto done; + } /* XXX fake reply and always send PK_OK ? */ /* * XXX this allows testing whether a user is allowed @@ -238,6 +242,7 @@ done: free(pkblob); free(key_s); free(ca_s); + free(sig); return authenticated; } -- 2.18.0