From 5d04ca6af739b82fd30d84d2783ca802ebfa1192 Mon Sep 17 00:00:00 2001 From: "djm@openbsd.org" Date: Mon, 6 Jul 2026 07:53:30 +0000 Subject: [PATCH] upstream: Fix multiple RFC 4462 (GSSAPIAuthentication) compliance problems 1) Remove an early failure return for GSSAPI authentication attempts made for invalid accounts that yielded different behaviour for valid vs invalid accounts. 2) Fix a situation where some GSSAPI requestes were not correctly subjected to MaxAuthTries. 3) Fix a moderate pre-authentication resource DoS related to #2. Add missing logging for error cases. Report and fixes from Manfred Kaiser, milCERT AT OpenBSD-Commit-ID: ca0acdd64eea435d6f89534538a9eb404a5629d3 CVE: CVE-2026-60000 Upstream: https://github.com/openssh/openssh-portable/commit/5d04ca6af739b82fd30d84d2783ca802ebfa1192 Signed-off-by: Thomas Perale --- auth2-gss.c | 55 ++++++++++++++++++++++++----------------------------- 1 file changed, 25 insertions(+), 30 deletions(-) diff --git a/auth2-gss.c b/auth2-gss.c index 355926afcd6e..85251b7d0b57 100644 --- a/auth2-gss.c +++ b/auth2-gss.c @@ -111,12 +111,6 @@ userauth_gssapi(struct ssh *ssh, const char *method) return (0); } - if (!authctxt->valid || authctxt->user == NULL) { - debug2_f("disabled because of invalid user"); - free(doid); - return (0); - } - if (GSS_ERROR(mm_ssh_gssapi_server_ctx(&ctxt, &goid))) { if (ctxt != NULL) ssh_gssapi_delete_ctx(&ctxt); @@ -178,8 +172,14 @@ input_gssapi_token(int type, uint32_t plen, struct ssh *ssh) (r = sshpkt_send(ssh)) != 0) fatal_fr(r, "send ERRTOK packet"); } + logit("Failed gssapi-with-mic for %s%.100s " + "from %.200s port %d ssh2", + authctxt->valid ? "" : "invalid user ", + authctxt->user, + ssh_remote_ipaddr(ssh), ssh_remote_port(ssh)); authctxt->postponed = 0; ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); + ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL); userauth_finish(ssh, 0, "gssapi-with-mic", NULL); } else { if (send_tok.length != 0) { @@ -191,14 +191,18 @@ input_gssapi_token(int type, uint32_t plen, struct ssh *ssh) fatal_fr(r, "send TOKEN packet"); } if (maj_status == GSS_S_COMPLETE) { - ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); - if (flags & GSS_C_INTEG_FLAG) - ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_MIC, + ssh_dispatch_set(ssh, + SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); + /* note: keep ERRTOK handler as per RFC 4462 s3.4 */ + if (flags & GSS_C_INTEG_FLAG) { + ssh_dispatch_set(ssh, + SSH2_MSG_USERAUTH_GSSAPI_MIC, &input_gssapi_mic); - else + } else { ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, &input_gssapi_exchange_complete); + } } } @@ -210,10 +214,6 @@ static int input_gssapi_errtok(int type, u_int32_t plen, struct ssh *ssh) { Authctxt *authctxt = ssh->authctxt; - Gssctxt *gssctxt; - gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER; - gss_buffer_desc recv_tok; - OM_uint32 maj_status; int r; u_char *p; size_t len; @@ -221,26 +221,21 @@ input_gssapi_errtok(int type, uint32_t plen, struct ssh *ssh) if (authctxt == NULL) fatal("No authentication or GSSAPI context"); - gssctxt = authctxt->methoddata; - if ((r = sshpkt_get_string(ssh, &p, &len)) != 0 || + /* Minimal error handling - just cancel auth and return FAILURE */ + if ((r = sshpkt_get_string_direct(ssh, NULL, NULL)) != 0 || (r = sshpkt_get_end(ssh)) != 0) fatal_fr(r, "parse packet"); - recv_tok.value = p; - recv_tok.length = len; - - /* Push the error token into GSSAPI to see what it says */ - maj_status = mm_ssh_gssapi_accept_ctx(gssctxt, &recv_tok, - &send_tok, NULL); - - free(recv_tok.value); - /* We can't return anything to the client, even if we wanted to */ + logit("Failed gssapi-with-mic for %s%.100s from %.200s port %d ssh2", + authctxt->valid ? "" : "invalid user ", + authctxt->user, + ssh_remote_ipaddr(ssh), ssh_remote_port(ssh)); + authctxt->postponed = 0; ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL); - - /* The client will have already moved on to the next auth */ - - gss_release_buffer(&maj_status, &send_tok); + ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_MIC, NULL); + ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL); + userauth_finish(ssh, 0, "gssapi-with-mic", NULL); return 0; }