[openssh-commits] [openssh] 05/06: upstream: Move check of public key type against allowed algorithms

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djm pushed a commit to branch master
in repository openssh.

commit 52154c2d232de1d5a161cb900bdb0792043ae142
Author: djm at openbsd.org <djm at openbsd.org>
AuthorDate: Thu Jul 30 03:37:39 2026 +0000

    upstream: Move check of public key type against allowed algorithms
    
    to before parsing of the key sent by the peer.
    
    This removes at least some key parsing and verification paths from
    the pre-auth attack surface.
    
    Suggested by Christopher Paul Rohlf of Anthropic, ok deraadt@
    
    OpenBSD-Commit-ID: 4560b53b5cd2fe9b875436e48995a1829c2a9dea
---
 auth2-hostbased.c | 13 +++++++------
 auth2-pubkey.c    | 12 ++++++------
 2 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/auth2-hostbased.c b/auth2-hostbased.c
index 8a1acdec3..564a8d3cc 100644
--- a/auth2-hostbased.c
+++ b/auth2-hostbased.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-hostbased.c,v 1.57 2026/04/02 07:48:13 djm Exp $ */
+/* $OpenBSD: auth2-hostbased.c,v 1.58 2026/07/30 03:37:39 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -88,6 +88,12 @@ userauth_hostbased(struct ssh *ssh, const char *method)
 		    pkalg);
 		goto done;
 	}
+	if (match_pattern_list(pkalg,
+	    options.hostbased_accepted_algos, 0) != 1) {
+		logit_f("signature algorithm %s not in "
+		    "HostbasedAcceptedAlgorithms", pkalg);
+		goto done;
+	}
 	if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
 		error_fr(r, "key_from_blob");
 		goto done;
@@ -102,11 +108,6 @@ userauth_hostbased(struct ssh *ssh, const char *method)
 		    "(received %s, expected %s)", sshkey_ssh_name(key), pkalg);
 		goto done;
 	}
-	if (match_pattern_list(pkalg, options.hostbased_accepted_algos, 0) != 1) {
-		logit_f("signature algorithm %s not in "
-		    "HostbasedAcceptedAlgorithms", pkalg);
-		goto done;
-	}
 	if ((r = sshkey_check_cert_sigtype(key,
 	    options.ca_sign_algorithms)) != 0) {
 		logit_fr(r, "certificate signature algorithm %s",
diff --git a/auth2-pubkey.c b/auth2-pubkey.c
index e446ef412..c15b1ba71 100644
--- a/auth2-pubkey.c
+++ b/auth2-pubkey.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-pubkey.c,v 1.126 2026/04/02 07:48:13 djm Exp $ */
+/* $OpenBSD: auth2-pubkey.c,v 1.127 2026/07/30 03:37:39 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  * Copyright (c) 2010 Damien Miller.  All rights reserved.
@@ -140,6 +140,11 @@ userauth_pubkey(struct ssh *ssh, const char *method)
 		verbose_f("unsupported public key algorithm: %s", pkalg);
 		goto done;
 	}
+	if (match_pattern_list(pkalg, options.pubkey_accepted_algos, 0) != 1) {
+		logit_f("signature algorithm %s not in "
+		    "PubkeyAcceptedAlgorithms", pkalg);
+		goto done;
+	}
 	if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
 		error_fr(r, "parse key");
 		goto done;
@@ -158,11 +163,6 @@ userauth_pubkey(struct ssh *ssh, const char *method)
 		logit("refusing previously-used %s key", sshkey_type(key));
 		goto done;
 	}
-	if (match_pattern_list(pkalg, options.pubkey_accepted_algos, 0) != 1) {
-		logit_f("signature algorithm %s not in "
-		    "PubkeyAcceptedAlgorithms", pkalg);
-		goto done;
-	}
 	if ((r = sshkey_check_cert_sigtype(key,
 	    options.ca_sign_algorithms)) != 0) {
 		logit_fr(r, "certificate signature algorithm %s",

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