From 8da33d6da86575cc1dfd109282de3c6345686327 Mon Sep 17 00:00:00 2001
From: "djm@openbsd.org" <djm@openbsd.org>
Date: Fri, 30 Oct 2026 03:22:47 +0000
Subject: [PATCH] upstream: harden private key serialisation API to avoid NULL

deref if it ever called with a public key.

Anthropic ANT-2026-MZ3ZOEX6

OpenBSD-Commit-ID: 037e85c68ca3a63329cffcaf7eb6ad0bdf6c7a14
---
 ssh-ecdsa.c   | 9 ++++++---
 ssh-ed25519.c | 4 +++-
 ssh-rsa.c     | 4 +++-
 sshkey.c      | 4 +++-
 4 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/ssh-ecdsa.c b/ssh-ecdsa.c
index 54a626e3f..ad69039b2 100644
--- a/ssh-ecdsa.c
+++ b/ssh-ecdsa.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-ecdsa.c,v 1.29 2026/02/14 00:18:34 jsg Exp $ */
+/* $OpenBSD: ssh-ecdsa.c,v 1.30 2026/10/30 03:22:47 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  * Copyright (c) 2010 Damien Miller.  All rights reserved.
@@ -147,13 +147,16 @@ ssh_ecdsa_serialize_private(const struct sshkey *key, struct sshbuf *b,
     enum sshkey_serialize_rep opts)
 {
 	int r;
+	const BIGNUM *priv;
 
+	if ((priv = EC_KEY_get0_private_key(
+	    EVP_PKEY_get0_EC_KEY(key->pkey))) == NULL)
+		return SSH_ERR_INVALID_ARGUMENT;
 	if (!sshkey_is_cert(key)) {
 		if ((r = ssh_ecdsa_serialize_public(key, b, opts)) != 0)
 			return r;
 	}
-	if ((r = sshbuf_put_bignum2(b,
-	    EC_KEY_get0_private_key(EVP_PKEY_get0_EC_KEY(key->pkey)))) != 0)
+	if ((r = sshbuf_put_bignum2(b, priv)) != 0)
 		return r;
 	return 0;
 }
diff --git a/ssh-ed25519.c b/ssh-ed25519.c
index e8113e8e9..adac89900 100644
--- a/ssh-ed25519.c
+++ b/ssh-ed25519.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-ed25519.c,v 1.24 2026/09/16 00:43:00 djm Exp $ */
+/* $OpenBSD: ssh-ed25519.c,v 1.25 2026/10/30 03:22:47 djm Exp $ */
 /*
  * Copyright (c) 2013 Markus Friedl <markus@openbsd.org>
  *
@@ -70,6 +70,8 @@ ssh_ed25519_serialize_private(const struct sshkey *key, struct sshbuf *b,
 {
 	int r;
 
+	if (key->ed25519_sk == NULL)
+		return SSH_ERR_INVALID_ARGUMENT;
 	if ((r = sshbuf_put_string(b, key->ed25519_pk, ED25519_PK_SZ)) != 0 ||
 	    (r = sshbuf_put_string(b, key->ed25519_sk, ED25519_SK_SZ)) != 0)
 		return r;
diff --git a/ssh-rsa.c b/ssh-rsa.c
index 7165b40ae..27304a045 100644
--- a/ssh-rsa.c
+++ b/ssh-rsa.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-rsa.c,v 1.85 2026/10/30 01:45:14 djm Exp $ */
+/* $OpenBSD: ssh-rsa.c,v 1.86 2026/10/30 03:22:47 djm Exp $ */
 /*
  * Copyright (c) 2000, 2003 Markus Friedl <markus@openbsd.org>
  *
@@ -99,6 +99,8 @@ ssh_rsa_serialize_private(const struct sshkey *key, struct sshbuf *b,
 	RSA_get0_key(rsa, &rsa_n, &rsa_e, &rsa_d);
 	RSA_get0_factors(rsa, &rsa_p, &rsa_q);
 	RSA_get0_crt_params(rsa, NULL, NULL, &rsa_iqmp);
+	if (rsa_d == NULL)
+		return SSH_ERR_INVALID_ARGUMENT;
 
 	if (!sshkey_is_cert(key)) {
 		/* Note: can't reuse ssh_rsa_serialize_public: e, n vs. n, e */
diff --git a/sshkey.c b/sshkey.c
index 8cd9e07af..6375d58bd 100644
--- a/sshkey.c
+++ b/sshkey.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.c,v 1.166 2026/10/30 01:34:10 djm Exp $ */
+/* $OpenBSD: sshkey.c,v 1.167 2026/10/30 03:22:47 djm Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Alexander von Gernler.  All rights reserved.
@@ -2560,6 +2560,8 @@ sshkey_serialize_private_sk(const struct sshkey *key, struct sshbuf *b)
 {
 	int r;
 
+	if (key->sk_key_handle == NULL)
+		return SSH_ERR_INVALID_ARGUMENT;
 	if ((r = sshbuf_put_cstring(b, key->sk_application)) != 0 ||
 	    (r = sshbuf_put_u8(b, key->sk_flags)) != 0 ||
 	    (r = sshbuf_put_stringb(b, key->sk_key_handle)) != 0 ||