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From Dirk-Willem van Gulik <di...@webweaving.org>
Subject [patch] - digest nonce including MM bump, doc and changes.
Date Thu, 18 Dec 2003 21:35:41 GMT

More complete patch, thanks for the feedback. Other options
include

->	kill mod_digest.c

and/or

->	move mod_auth_digest.c from exp. into standard

as this fix requires a MM bump _or_ so much rewriting that
it may be easier to spend some cycles on mod_auth_digest.c.

Dw

Index: src/ApacheCore.def
===================================================================
RCS file: /home/cvs/apache-1.3/src/ApacheCore.def,v
retrieving revision 1.35
diff -u -r1.35 ApacheCore.def
--- src/ApacheCore.def	18 Jun 2002 04:19:46 -0000	1.35
+++ src/ApacheCore.def	18 Dec 2003 21:25:49 -0000
@@ -447,3 +447,4 @@
         ap_getline @439
         ap_get_chunk_size @440
         ap_escape_logitem @441
+	ap_auth_nonce @442
Index: src/ApacheCoreOS2.def
===================================================================
RCS file: /home/cvs/apache-1.3/src/ApacheCoreOS2.def,v
retrieving revision 1.13
diff -u -r1.13 ApacheCoreOS2.def
--- src/ApacheCoreOS2.def	22 May 2003 09:45:28 -0000	1.13
+++ src/ApacheCoreOS2.def	18 Dec 2003 21:25:50 -0000
@@ -430,3 +430,4 @@
 	ap_escape_logitem @441
 	ap_popenf_ex @442
 	ap_psocket_ex @443
+	ap_auth_nonce @444
Index: src/CHANGES
===================================================================
RCS file: /home/cvs/apache-1.3/src/CHANGES,v
retrieving revision 1.1914
diff -u -r1.1914 CHANGES
--- src/CHANGES	14 Dec 2003 18:16:49 -0000	1.1914
+++ src/CHANGES	18 Dec 2003 21:25:56 -0000
@@ -1,5 +1,11 @@
 Changes with Apache 1.3.30

+  *) SECURITY - verification as to wether the nonce returned in the
+     client response is one we issued ourselves by means of a
+     AuthNonce secret exposed as an md5(). See mod_digest documentation
+     for more details. The experimental/mod_auth_digest.c does not
+     have this issue.  [Dirk-Willem van Gulik]
+
   *) SECURITY [CAN-2003-0020]: Escape arbitrary data before writing
      into the errorlog.  [André Malo]

Index: src/include/ap_mmn.h
===================================================================
RCS file: /home/cvs/apache-1.3/src/include/ap_mmn.h,v
retrieving revision 1.65
diff -u -r1.65 ap_mmn.h
--- src/include/ap_mmn.h	14 Dec 2003 18:16:49 -0000	1.65
+++ src/include/ap_mmn.h	18 Dec 2003 21:25:56 -0000
@@ -244,6 +244,8 @@
  *                        ap_popenf_ex() and ap_psocket_ex().
  * 19990320.15          - ap_is_recursion_limit_exceeded()
  * 19990320.16          - ap_escape_errorlog_item()
+ * 20031212 1.3.30-dev  - ap_auth_nonce() and auth_nonce added
+ *                        in the request_rec.
  */

 #define MODULE_MAGIC_COOKIE 0x41503133UL /* "AP13" */
Index: src/include/http_core.h
===================================================================
RCS file: /home/cvs/apache-1.3/src/include/http_core.h,v
retrieving revision 1.71
diff -u -r1.71 http_core.h
--- src/include/http_core.h	7 Jul 2003 00:34:09 -0000	1.71
+++ src/include/http_core.h	18 Dec 2003 21:25:56 -0000
@@ -162,6 +162,7 @@

 API_EXPORT(const char *) ap_auth_type (request_rec *);
 API_EXPORT(const char *) ap_auth_name (request_rec *);
+API_EXPORT(const char *) ap_auth_nonce (request_rec *);
 API_EXPORT(int) ap_satisfies (request_rec *r);
 API_EXPORT(const array_header *) ap_requires (request_rec *);

@@ -244,6 +245,7 @@
     int satisfy;
     char *ap_auth_type;
     char *ap_auth_name;
+    char *ap_auth_nonce;	/* digest auth */
     array_header *ap_requires;

     /* Custom response config. These can contain text or a URL to redirect to.
Index: src/main/http_core.c
===================================================================
RCS file: /home/cvs/apache-1.3/src/main/http_core.c,v
retrieving revision 1.327
diff -u -r1.327 http_core.c
--- src/main/http_core.c	17 Nov 2003 17:14:53 -0000	1.327
+++ src/main/http_core.c	18 Dec 2003 21:25:58 -0000
@@ -236,6 +236,9 @@
     if (new->ap_auth_name) {
         conf->ap_auth_name = new->ap_auth_name;
     }
+    if (new->ap_auth_nonce) {
+        conf->ap_auth_nonce= new->ap_auth_nonce;
+    }
     if (new->ap_requires) {
         conf->ap_requires = new->ap_requires;
     }
@@ -577,6 +580,29 @@
     return conf->ap_auth_name;
 }

+API_EXPORT(const char *) ap_auth_nonce(request_rec *r)
+{
+    core_dir_config *conf;
+    conf = (core_dir_config *)ap_get_module_config(r->per_dir_config,
+						   &core_module);
+    if (conf->ap_auth_nonce)
+	return conf->ap_auth_nonce;
+
+    /* Ideally we'd want to mix in some per-directory style
+     * information; as we are likely to want to detect replay
+     * across those boundaries and some randomness. But that
+     * is harder due to the adhoc nature of .htaccess memory
+     * structures, restarts and forks.
+     *
+     * But then again - you should use AuthNonce in your config
+     * file if you care. So the adhoc value should do.
+     */
+    return ap_psprintf(r->pool,"%lu%lu%lu%lu%lu%s",
+	*(unsigned long *)&((r->connection->local_addr).sin_addr ),
+	ap_user_name, ap_listeners, ap_server_argv0, ap_pid_fname
+    );
+}
+
 API_EXPORT(const char *) ap_default_type(request_rec *r)
 {
     core_dir_config *conf;
@@ -2797,6 +2823,28 @@
     return NULL;
 }

+/*
+ * Load an authorisation nonce into our location configuration, and
+ * force it to be in the 0-9/A-Z realm.
+ */
+static const char *set_authnonce (cmd_parms *cmd, void *mconfig, char *word1)
+{
+    core_dir_config *aconfig = (core_dir_config *)mconfig;
+    int i;
+
+    aconfig->ap_auth_nonce = ap_escape_quotes(cmd->pool, word1);
+
+    if (strlen(aconfig->ap_auth_nonce) > 510)
+		return "AuthNonce length limited to 510 chars for browser compatibility";
+
+    for(i=0;i<strlen(aconfig->ap_auth_nonce );i++)
+	if (!ap_isalnum(aconfig->ap_auth_nonce [i]))
+		return "AuthNonce limited to 0-9 and A-Z range for browser compatibility";
+
+    return NULL;
+}
+
+
 #ifdef _OSD_POSIX /* BS2000 Logon Passwd file */
 static const char *set_bs2000_account(cmd_parms *cmd, void *dummy, char *name)
 {
@@ -3411,6 +3459,9 @@
   "An HTTP authorization type (e.g., \"Basic\")" },
 { "AuthName", set_authname, NULL, OR_AUTHCFG, TAKE1,
   "The authentication realm (e.g. \"Members Only\")" },
+{ "AuthNonce", set_authnonce, NULL, OR_AUTHCFG, TAKE1,
+  "An authentication token which should be different for each logical realm. "\
+  "A random value or the servers IP may be a good choise.\n" },
 { "Require", require, NULL, OR_AUTHCFG, RAW_ARGS,
   "Selects which authenticated users or groups may access a protected space" },
 { "Satisfy", satisfy, NULL, OR_AUTHCFG, TAKE1,
Index: src/main/http_protocol.c
===================================================================
RCS file: /home/cvs/apache-1.3/src/main/http_protocol.c,v
retrieving revision 1.330
diff -u -r1.330 http_protocol.c
--- src/main/http_protocol.c	3 Feb 2003 17:13:22 -0000	1.330
+++ src/main/http_protocol.c	18 Dec 2003 21:26:00 -0000
@@ -76,6 +76,7 @@
 #include "util_date.h"          /* For parseHTTPdate and BAD_DATE */
 #include <stdarg.h>
 #include "http_conf_globals.h"
+#include "util_md5.h"		/* For digestAuth */

 #define SET_BYTES_SENT(r) \
   do { if (r->sent_bodyct) \
@@ -1391,11 +1392,24 @@

 API_EXPORT(void) ap_note_digest_auth_failure(request_rec *r)
 {
+    /* We need to create a nonce which:
+     * a) changes all the time (see r->request_time)
+     *    below and
+     * b) of which we can verify that it is our own
+     *    fairly easily when it comes to veryfing
+     *    the digest coming back in the response.
+     * c) and which as a whole should not
+     *    be unlikely to be in use anywhere else.
+     */
+    char * nonce_prefix = ap_md5(r->pool,
+	ap_psprintf(r->pool, "%s%lu",
+		ap_auth_nonce(r), r->request_time));
+
     ap_table_setn(r->err_headers_out,
 	    r->proxyreq == STD_PROXY ? "Proxy-Authenticate"
 		  : "WWW-Authenticate",
-	    ap_psprintf(r->pool, "Digest realm=\"%s\", nonce=\"%lu\"",
-		ap_auth_name(r), r->request_time));
+	    ap_psprintf(r->pool, "Digest realm=\"%s\", nonce=\"%s%lu\"",
+		ap_auth_name(r), nonce_prefix, r->request_time));
 }

 API_EXPORT(int) ap_get_basic_auth_pw(request_rec *r, const char **pw)
Index: src/modules/standard/mod_digest.c
===================================================================
RCS file: /home/cvs/apache-1.3/src/modules/standard/mod_digest.c,v
retrieving revision 1.52
diff -u -r1.52 mod_digest.c
--- src/modules/standard/mod_digest.c	3 Feb 2003 17:13:27 -0000	1.52
+++ src/modules/standard/mod_digest.c	18 Dec 2003 21:26:00 -0000
@@ -316,6 +316,23 @@

 /* The actual MD5 code... whee */

+/* Check that a given nonce is actually one which was
+ * issued by this server in the right context.
+ */
+static int check_nonce(pool *p, char * prefix, const char * nonce) {
+    char * timestamp = (char *)nonce + 2 * MD5_DIGESTSIZE;
+    char * md5;
+
+    if (strlen(nonce) < MD5_DIGESTSIZE)
+     	return AUTH_REQUIRED;
+
+    md5 = ap_md5(p, ap_pstrcat(p, prefix, timestamp, NULL));
+
+    return strncmp(md5, nonce, 2 * MD5_DIGESTSIZE);
+}
+
+/* Check the digest itself.
+ */
 static char *find_digest(request_rec *r, digest_header_rec * h, char *a1)
 {
     return ap_md5(r->pool,
@@ -339,7 +356,6 @@
 /* Determine user ID, and check if it really is that user, for HTTP
  * basic authentication...
  */
-
 static int authenticate_digest_user(request_rec *r)
 {
     digest_config_rec *sec =
@@ -355,7 +371,16 @@

     if (!sec->pwfile)
 	return DECLINED;
-
+
+    /* Check that the nonce was one we actually issued. */
+    if (check_nonce(r->pool, ap_auth_nonce(r), response->nonce)) {
+	ap_log_rerror(APLOG_MARK, APLOG_NOERRNO|APLOG_ERR, r,
+		    "Client is using a nonce which was not issued by "
+                    "this server for this context: %s", r->uri);
+	ap_note_digest_auth_failure(r);
+	return AUTH_REQUIRED;
+    }
+
     if (!(a1 = get_hash(r, c->user, sec->pwfile))) {
 	ap_log_rerror(APLOG_MARK, APLOG_NOERRNO|APLOG_ERR, r,
 		    "user %s not found: %s", c->user, r->uri);
Index: htdocs/manual/mod/mod_digest.html
===================================================================
RCS file: /home/cvs/httpd-docs-1.3/htdocs/manual/mod/mod_digest.html,v
retrieving revision 1.14
diff -u -r1.14 mod_digest.html
--- htdocs/manual/mod/mod_digest.html	23 Jan 2002 02:51:03 -0000	1.14
+++ htdocs/manual/mod/mod_digest.html	18 Dec 2003 21:26:51 -0000
@@ -48,17 +48,28 @@
     <p>Using MD5 Digest authentication is very simple. Simply set
     up authentication normally. However, use "AuthType Digest" and
     "AuthDigestFile" instead of the normal "AuthType Basic" and
-    "AuthUserFile". Everything else should remain the same.</p>
+    "AuthUserFile".
+
+    <p>As to make sure that replay is not possible across
+    sections of the site, or across sites (assuming a realm,
+    userid and password are valid in that wider context) a
+    secret nonce prefix can be configured with the
+    core directive <a href="core.html#AuthNonce">AuthNonce</a>.
+    </p>
+    <p>If none if configured a sensible, but not particular
+    secure, default is used. When used in load balancing
+    situations the prefix should be shared across servers.
+    </p>
+    <p>The experimental <a href="mod_auth_digest.html">mod_auth_digest</a>
+    module offers a number of additinal protections against replay.
+    </p>
+
+    <p>Everything else should remain the same.</p>

     <p>MD5 authentication provides a more secure password system,
     but only works with supporting browsers. As of this writing
-    (January 2002), the only major browsers which support digest
-    authentication are <a href="http://www.opera.com/">Opera 4.0</a>,
-    <a href="http://www.microsoft.com/windows/ie/">MS Internet
-    Explorer 5.0</a> and <a href="http://www.w3.org/Amaya/">Amaya</a>.
-    Therefore, we do not recommend using this feature on a large
-    Internet site. However, for personal and intra-net use, where
-    browser users can be controlled, it is ideal.</p>
+    (December 2003), most major browsers support digest authentication.
+    </p>

     <p>See also <a href="mod_auth_digest.html">mod_auth_digest</a>,
     which is an updated version of this module, in order to determine
Index: htdocs/manual/mod/core.html.en
===================================================================
RCS file: /home/cvs/httpd-docs-1.3/htdocs/manual/mod/core.html.en,v
retrieving revision 1.257
diff -u -r1.257 core.html.en
--- htdocs/manual/mod/core.html.en      3 Dec 2003 10:35:24 -0000
1.257
+++ htdocs/manual/mod/core.html.en      18 Dec 2003 21:36:14 -0000
@@ -37,6 +37,8 @@

       <li><a href="#authname">AuthName</a></li>

+      <li><a href="#AuthNonce">AuthNonce</a></li>
+
       <li><a href="#authtype">AuthType</a></li>

       <li><a href="#bindaddress">BindAddress</a></li>
@@ -498,6 +500,7 @@
       href="mod_auth_dbm.html#authdbmuserfile">AuthDBMUserFile</a>,
       <a href="mod_auth.html#authgroupfile">AuthGroupFile</a>, <a
       href="#authname">AuthName</a>, <a
+      href="#AuthNonce">AuthNonce</a>, <a
       href="#authtype">AuthType</a>, <a
       href="mod_auth.html#authuserfile">AuthUserFile</a>, <a
       href="#require">Require</a>, <em>etc.</em>).</dd>
@@ -593,6 +596,42 @@
     Access Control</a></p>
     <hr />

+    <h2><a id="AuthNonce" name="AuthNonce">AuthNonce
+    directive</a></h2>
+
+    <a href="directive-dict.html#Syntax"
+    rel="Help"><strong>Syntax:</strong></a> AuthNonce
+    <em>secret-real-string</em><br />
+     <a href="directive-dict.html#Context"
+    rel="Help"><strong>Context:</strong></a> directory,
+    .htaccess<br />
+     <a href="directive-dict.html#Override"
+    rel="Help"><strong>Override:</strong></a> AuthConfig<br />
+     <a href="directive-dict.html#Status"
+    rel="Help"><strong>Status:</strong></a> core
+
+    <p>This directive sets a per realm secret nonce prefix
+    which is used to ensure that a captured username, password
+    and realm string during a Digest exchange cannot
+    be replayed at other places.
+    </p>
+    <p>It only applies to <a href="mod_digest.html">mod_digest.html</a>,
+    the experimental <a
href="mod_auth_digest.html">mod_auth_digest.html</a>
+    implements its own (more advanced and also time sensitive) replay
protection.
+    </p>
+
+    It must be accompanied by <a href="#authtype">AuthType</a> of
+    type Digest, one or more
+    <a href="#require">Require</a> directives, and directives such
+    as <a href="mod_auth.html#authuserfile">AuthUserFile</a> and <a
+    href="mod_auth.html#authgroupfile">AuthGroupFile</a> to
+    work.</p>
+
+    <p><strong>See also:</strong> <a
+    href="../howto/auth.html">Authentication, Authorization, and
+    Access Control</a></p>
+    <hr />
+
     <h2><a id="authtype" name="authtype">AuthType
     directive</a></h2>

@@ -616,6 +655,9 @@
     as <a href="mod_auth.html#authuserfile">AuthUserFile</a> and <a
     href="mod_auth.html#authgroupfile">AuthGroupFile</a> to
     work.</p>
+
+    <p>When AuthDigest is used an <a href="#AuthNonce">AuthNonce</a>
+    should also be set.</p>

     <p><strong>See also:</strong> <a
     href="../howto/auth.html">Authentication, Authorization, and

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