Security Fix (CAN-2003-0987):
mod_digest for Apache did not properly verify the nonce of a client
response by using a AuthNonce secret. Now Apache verifies the nonce
returned in the client response to check whether it was issued by itself
by means of a AuthDigestRealmSeed secret exposed as an md5().
Index: src/include/http_core.h
--- src/include/http_core.h.orig 2003-07-07 02:34:09.000000000 +0200
+++ src/include/http_core.h 2004-05-12 10:03:51.000000000 +0200
@@ -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 *);
@@ -355,6 +356,9 @@
*/
ap_flag_e cgi_command_args;
+ /* Digest auth. */
+ char *ap_auth_nonce;
+
} core_dir_config;
/* Per-server core configuration */
Index: src/main/http_core.c
--- src/main/http_core.c.orig 2003-10-19 15:20:57.000000000 +0200
+++ src/main/http_core.c 2004-05-12 10:03:51.000000000 +0200
@@ -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 +580,31 @@
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 AuthDigestRealmSeed in your config
+ * file if you care. So the adhoc value should do.
+ */
+ return ap_psprintf(r->pool,"%pp%pp%pp%pp%pp",
+ (void *)&((r->connection->local_addr).sin_addr ),
+ (void *)ap_user_name,
+ (void *)ap_listeners,
+ (void *)ap_server_argv0,
+ (void *)ap_pid_fname);
+}
+
API_EXPORT(const char *) ap_default_type(request_rec *r)
{
core_dir_config *conf;
@@ -2786,6 +2814,28 @@
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;
+ size_t i;
+
+ aconfig->ap_auth_nonce = ap_escape_quotes(cmd->pool, word1);
+
+ if (strlen(aconfig->ap_auth_nonce) > 510)
+ return "AuthDigestRealmSeed 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 "AuthDigestRealmSeed 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)
{
@@ -3400,6 +3450,9 @@
"An HTTP authorization type (e.g., \"Basic\")" },
{ "AuthName", set_authname, NULL, OR_AUTHCFG, TAKE1,
"The authentication realm (e.g. \"Members Only\")" },
+{ "AuthDigestRealmSeed", 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
--- src/main/http_protocol.c.orig 2003-02-03 18:13:22.000000000 +0100
+++ src/main/http_protocol.c 2004-05-12 10:03:51.000000000 +0200
@@ -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 +1392,25 @@
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,
+ (unsigned char *)
+ 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
--- src/modules/standard/mod_digest.c.orig 2003-02-03 18:13:27.000000000 +0100
+++ src/modules/standard/mod_digest.c 2004-05-12 10:03:51.000000000 +0200
@@ -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, const 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, (unsigned char *)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,
@@ -356,6 +373,15 @@
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);
