CVE-2016-10009 (published 2017-01-05T02:59Z)

Untrusted search path vulnerability in ssh-agent.c in ssh-agent in OpenSSH before 7.4 allows remote attackers to execute arbitrary local PKCS#11 modules by leveraging control over a forwarded agent-socket.

Severity: HIGH
CVSS v2 base score: 7.5 (AV:N/AC:L/Au:N/C:P/I:P/A:P)
CVSS v3 base score: 7.3, HIGH (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L)

Weakness information:
cwe_id: CWE-426
cwe_name: Untrusted Search Path
description: The product searches for critical resources using an externally-supplied search path that can point to resources that are not under the product's direct control.
extended_description: 
            This might allow attackers to execute their own programs, access unauthorized data files, or modify configuration in unexpected ways. If the product uses a search path to locate critical resources such as programs, then an attacker could modify that search path to point to a malicious program, which the targeted product would then execute. The problem extends to any type of critical resource that the product trusts.
            Some of the most common variants of untrusted search path are:
               
                  In various UNIX and Linux-based systems, the PATH environment variable may be consulted to locate executable programs, and LD_PRELOAD may be used to locate a separate library.
                  In various Microsoft-based systems, the PATH environment variable is consulted to locate a DLL, if the DLL is not found in other paths that appear earlier in the search order.
               
         
         

Fix information:
repo_url: https://github.com/openbsd/src
commit_details: repo_url: https://github.com/openbsd/src
author: djm
author_date: 2016-11-30 03:07:37+00:00
msg: add a whitelist of paths from which ssh-agent will load (via
ssh-pkcs11-helper) a PKCS#11 module; ok markus@
repository: repo_url: https://github.com/openbsd/src
repo_name: openbsd/src
description: Read-only git conversion of OpenBSD's official CVS src repository. Pull requests not accepted - send diffs to the tech@ mailing list.
repo_language: C
owner: openbsd
file_changes: filename: ssh-agent.1
change_type: ModificationType.MODIFY
diff: @@ -1,4 +1,4 @@
-.\" $OpenBSD: ssh-agent.1,v 1.62 2015/11/15 23:54:15 jmc Exp $
+.\" $OpenBSD: ssh-agent.1,v 1.63 2016/11/30 03:07:37 djm Exp $
 .\"
 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -34,7 +34,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: November 15 2015 $
+.Dd $Mdocdate: November 30 2016 $
 .Dt SSH-AGENT 1
 .Os
 .Sh NAME
@@ -47,6 +47,7 @@
 .Op Fl a Ar bind_address
 .Op Fl E Ar fingerprint_hash
 .Op Fl t Ar life
+.Op Fl P Ar pkcs11_whitelist
 .Op Ar command Op Ar arg ...
 .Nm ssh-agent
 .Op Fl c | s
@@ -121,6 +122,18 @@ The default is
 Kill the current agent (given by the
 .Ev SSH_AGENT_PID
 environment variable).
+.It Fl P
+Specify a pattern-list of acceptable paths for PKCS#11 shared libraries
+that may be added using the
+.Fl s
+option to
+.Xr ssh-add 1 .
+The default is to allow loading PKCS#11 libraries from
+.Dq /usr/lib/*,/usr/local/lib/* .
+PKCS#11 libraries that do not match the whitelist will be refused.
+See PATTERNS in
+.Xr ssh_config 5
+for a description of pattern-list syntax.
 .It Fl s
 Generate Bourne shell commands on
 .Dv stdout .

programming_language: Shell
filename: ssh-agent.c
change_type: ModificationType.MODIFY
diff: @@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-agent.c,v 1.214 2016/09/12 01:22:38 deraadt Exp $ */
+/* $OpenBSD: ssh-agent.c,v 1.215 2016/11/30 03:07:37 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -69,11 +69,16 @@
 #include "misc.h"
 #include "digest.h"
 #include "ssherr.h"
+#include "match.h"
 
 #ifdef ENABLE_PKCS11
 #include "ssh-pkcs11.h"
 #endif
 
+#ifndef DEFAULT_PKCS11_WHITELIST
+# define DEFAULT_PKCS11_WHITELIST "/usr/lib/*,/usr/local/lib/*"
+#endif
+
 typedef enum {
 	AUTH_UNUSED,
 	AUTH_SOCKET,
@@ -121,6 +126,9 @@ pid_t cleanup_pid = 0;
 char socket_name[PATH_MAX];
 char socket_dir[PATH_MAX];
 
+/* PKCS#11 path whitelist */
+static char *pkcs11_whitelist;
+
 /* locking */
 #define LOCK_SIZE	32
 #define LOCK_SALT_SIZE	16
@@ -724,7 +732,7 @@ no_identities(SocketEntry *e, u_int type)
 static void
 process_add_smartcard_key(SocketEntry *e)
 {
-	char *provider = NULL, *pin;
+	char *provider = NULL, *pin, canonical_provider[PATH_MAX];
 	int r, i, version, count = 0, success = 0, confirm = 0;
 	u_int seconds;
 	time_t death = 0;
@@ -756,10 +764,21 @@ process_add_smartcard_key(SocketEntry *e)
 			goto send;
 		}
 	}
+	if (realpath(provider, canonical_provider) == NULL) {
+		verbose("failed PKCS#11 add of \"%.100s\": realpath: %s",
+		    provider, strerror(errno));
+		goto send;
+	}
+	if (match_pattern_list(canonical_provider, pkcs11_whitelist, 0) != 1) {
+		verbose("refusing PKCS#11 add of \"%.100s\": "
+		    "provider not whitelisted", canonical_provider);
+		goto send;
+	}
+	debug("%s: add %.100s", __func__, canonical_provider);
 	if (lifetime && !death)
 		death = monotime() + lifetime;
 
-	count = pkcs11_add_provider(provider, pin, &keys);
+	count = pkcs11_add_provider(canonical_provider, pin, &keys);
 	for (i = 0; i < count; i++) {
 		k = keys[i];
 		version = k->type == KEY_RSA1 ? 1 : 2;
@@ -767,8 +786,8 @@ process_add_smartcard_key(SocketEntry *e)
 		if (lookup_identity(k, version) == NULL) {
 			id = xcalloc(1, sizeof(Identity));
 			id->key = k;
-			id->provider = xstrdup(provider);
-			id->comment = xstrdup(provider); /* XXX */
+			id->provider = xstrdup(canonical_provider);
+			id->comment = xstrdup(canonical_provider); /* XXX */
 			id->death = death;
 			id->confirm = confirm;
 			TAILQ_INSERT_TAIL(&tab->idlist, id, next);
@@ -1157,7 +1176,7 @@ usage(void)
 {
 	fprintf(stderr,
 	    "usage: ssh-agent [-c | -s] [-Dd] [-a bind_address] [-E fingerprint_hash]\n"
-	    "                 [-t life] [command [arg ...]]\n"
+	    "                 [-P pkcs11_whitelist] [-t life] [command [arg ...]]\n"
 	    "       ssh-agent [-c | -s] -k\n");
 	exit(1);
 }
@@ -1191,7 +1210,7 @@ main(int ac, char **av)
 	OpenSSL_add_all_algorithms();
 #endif
 
-	while ((ch = getopt(ac, av, "cDdksE:a:t:")) != -1) {
+	while ((ch = getopt(ac, av, "cDdksE:a:P:t:")) != -1) {
 		switch (ch) {
 		case 'E':
 			fingerprint_hash = ssh_digest_alg_by_name(optarg);
@@ -1206,6 +1225,11 @@ main(int ac, char **av)
 		case 'k':
 			k_flag++;
 			break;
+		case 'P':
+			if (pkcs11_whitelist != NULL)
+				fatal("-P option already specified");
+			pkcs11_whitelist = xstrdup(optarg);
+			break;
 		case 's':
 			if (c_flag)
 				usage();
@@ -1240,6 +1264,9 @@ main(int ac, char **av)
 	if (ac > 0 && (c_flag || k_flag || s_flag || d_flag || D_flag))
 		usage();
 
+	if (pkcs11_whitelist == NULL)
+		pkcs11_whitelist = xstrdup(DEFAULT_PKCS11_WHITELIST);
+
 	if (ac == 0 && !c_flag && !s_flag) {
 		shell = getenv("SHELL");
 		if (shell != NULL && (len = strlen(shell)) > 2 &&
@@ -1385,7 +1412,7 @@ skip:
 	signal(SIGTERM, cleanup_handler);
 	nalloc = 0;
 
-	if (pledge("stdio cpath unix id proc exec", NULL) == -1)
+	if (pledge("stdio rpath cpath unix id proc exec", NULL) == -1)
 		fatal("%s: pledge: %s", __progname, strerror(errno));
 
 	while (1) {

programming_language: C