Fix a weakness that allows remote code execution via the Transmission
RPC server using DNS rebinding:
https://bugs.chromium.org/p/project-zero/issues/detail?id=1447
Patch adapted from Tavis Ormandy's patch on the Transmission master
branch to the Transmission 2.92 release by Leo Famulari
<leo@famulari.name>:
https://github.com/transmission/transmission/pull/468/commits
From fe2d3c6e75088f3d9b6040ce06da3d530358bc2f Mon Sep 17 00:00:00 2001
From: Tavis Ormandy <taviso@google.com>
Date: Thu, 11 Jan 2018 10:00:41 -0800
Subject: [PATCH] mitigate dns rebinding attacks against daemon
---
libtransmission/quark.c | 2 +
libtransmission/quark.h | 2 +
libtransmission/rpc-server.c | 116 +++++++++++++++++++++++++++++++++++++----
libtransmission/rpc-server.h | 4 ++
libtransmission/session.c | 2 +
libtransmission/transmission.h | 1 +
libtransmission/web.c | 3 ++
7 files changed, 121 insertions(+), 9 deletions(-)
diff --git a/libtransmission/quark.c b/libtransmission/quark.c
index 30cc2bca4..b4fd7aabd 100644
--- a/libtransmission/quark.c
+++ b/libtransmission/quark.c
@@ -289,6 +289,8 @@ static const struct tr_key_struct my_static[] =
{ "rpc-authentication-required", 27 },
{ "rpc-bind-address", 16 },
{ "rpc-enabled", 11 },
+ { "rpc-host-whitelist", 18 },
+ { "rpc-host-whitelist-enabled", 26 },
{ "rpc-password", 12 },
{ "rpc-port", 8 },
{ "rpc-url", 7 },
diff --git a/libtransmission/quark.h b/libtransmission/quark.h
index 7f5212733..17464be8f 100644
--- a/libtransmission/quark.h
+++ b/libtransmission/quark.h
@@ -291,6 +291,8 @@ enum
TR_KEY_rpc_authentication_required,
TR_KEY_rpc_bind_address,
TR_KEY_rpc_enabled,
+ TR_KEY_rpc_host_whitelist,
+ TR_KEY_rpc_host_whitelist_enabled,
TR_KEY_rpc_password,
TR_KEY_rpc_port,
TR_KEY_rpc_url,
diff --git a/libtransmission/rpc-server.c b/libtransmission/rpc-server.c
index a3485f3fa..292cd5fce 100644
--- a/libtransmission/rpc-server.c
+++ b/libtransmission/rpc-server.c
@@ -52,6 +52,7 @@ struct tr_rpc_server
bool isEnabled;
bool isPasswordEnabled;
bool isWhitelistEnabled;
+ bool isHostWhitelistEnabled;
tr_port port;
char * url;
struct in_addr bindAddress;
@@ -63,6 +64,7 @@ struct tr_rpc_server
char * password;
char * whitelistStr;
tr_list * whitelist;
+ tr_list * hostWhitelist;
char * sessionId;
time_t sessionIdExpiresAt;
@@ -588,6 +590,49 @@ isAddressAllowed (const tr_rpc_server * server, const char * address)
return false;
}
+static bool isHostnameAllowed(tr_rpc_server const* server, struct evhttp_request* req)
+{
+ /* If password auth is enabled, any hostname is permitted. */
+ if (server->isPasswordEnabled)
+ {
+ return true;
+ }
+
+ char const* const host = evhttp_find_header(req->input_headers, "Host");
+
+ // If whitelist is disabled, no restrictions.
+ if (!server->isHostWhitelistEnabled)
+ return true;
+
+ /* No host header, invalid request. */
+ if (host == NULL)
+ {
+ return false;
+ }
+
+ /* Host header might include the port. */
+ char* const hostname = tr_strndup(host, strcspn(host, ":"));
+
+ /* localhost or ipaddress is always acceptable. */
+ if (strcmp(hostname, "localhost") == 0 || strcmp(hostname, "localhost.") == 0 || tr_addressIsIP(hostname))
+ {
+ tr_free(hostname);
+ return true;
+ }
+
+ /* Otherwise, hostname must be whitelisted. */
+ for (tr_list* l = server->hostWhitelist; l != NULL; l = l->next) {
+ if (tr_wildmat(hostname, l->data))
+ {
+ tr_free(hostname);
+ return true;
+ }
+ }
+
+ tr_free(hostname);
+ return false;
+}
+
static bool
test_session_id (struct tr_rpc_server * server, struct evhttp_request * req)
{
@@ -663,6 +708,23 @@ handle_request (struct evhttp_request * req, void * arg)
handle_upload (req, server);
}
#ifdef REQUIRE_SESSION_ID
+ else if (!isHostnameAllowed(server, req))
+ {
+ char* tmp = tr_strdup_printf(
+ "<p>Transmission received your request, but the hostname was unrecognized.</p>"
+ "<p>To fix this, choose one of the following options:"
+ "<ul>"
+ "<li>Enable password authentication, then any hostname is allowed.</li>"
+ "<li>Add the hostname you want to use to the whitelist in settings.</li>"
+ "</ul></p>"
+ "<p>If you're editing settings.json, see the 'rpc-host-whitelist' and 'rpc-host-whitelist-enabled' entries.</p>"
+ "<p>This requirement has been added to help prevent "
+ "<a href=\"https://en.wikipedia.org/wiki/DNS_rebinding\">DNS Rebinding</a> "
+ "attacks.</p>");
+ send_simple_response(req, 421, tmp);
+ tr_free(tmp);
+ }
+
else if (!test_session_id (server, req))
{
const char * sessionId = get_current_session_id (server);
@@ -674,7 +736,7 @@ handle_request (struct evhttp_request * req, void * arg)
"<li> When you get this 409 error message, resend your request with the updated header"
"</ol></p>"
"<p>This requirement has been added to help prevent "
- "<a href=\"http://en.wikipedia.org/wiki/Cross-site_request_forgery\">CSRF</a> "
+ "<a href=\"https://en.wikipedia.org/wiki/Cross-site_request_forgery\">CSRF</a> "
"attacks.</p>"
"<p><code>%s: %s</code></p>",
TR_RPC_SESSION_ID_HEADER, sessionId);
@@ -875,19 +937,14 @@ tr_rpcGetUrl (const tr_rpc_server * server)
return server->url ? server->url : "";
}
-void
-tr_rpcSetWhitelist (tr_rpc_server * server, const char * whitelistStr)
+static void
+tr_rpcSetList (char const* whitelistStr, tr_list** list)
{
void * tmp;
const char * walk;
- /* keep the string */
- tmp = server->whitelistStr;
- server->whitelistStr = tr_strdup (whitelistStr);
- tr_free (tmp);
-
/* clear out the old whitelist entries */
- while ((tmp = tr_list_pop_front (&server->whitelist)))
+ while ((tmp = tr_list_pop_front (list)) != NULL)
tr_free (tmp);
/* build the new whitelist entries */
@@ -896,7 +953,7 @@ tr_rpcSetWhitelist (tr_rpc_server * server, const char * whitelistStr)
const char * delimiters = " ,;";
const size_t len = strcspn (walk, delimiters);
char * token = tr_strndup (walk, len);
- tr_list_append (&server->whitelist, token);
+ tr_list_append (list, token);
if (strcspn (token, "+-") < len)
tr_logAddNamedInfo (MY_NAME, "Adding address to whitelist: %s (And it has a '+' or '-'! Are you using an old ACL by mistake?)", token);
else
@@ -909,6 +966,21 @@ tr_rpcSetWhitelist (tr_rpc_server * server, const char * whitelistStr)
}
}
+void tr_rpcSetHostWhitelist(tr_rpc_server* server, char const* whitelistStr)
+{
+ tr_rpcSetList(whitelistStr, &server->hostWhitelist);
+}
+
+void tr_rpcSetWhitelist(tr_rpc_server* server, char const* whitelistStr)
+{
+ /* keep the string */
+ char* const tmp = server->whitelistStr;
+ server->whitelistStr = tr_strdup(whitelistStr);
+ tr_free(tmp);
+
+ tr_rpcSetList(whitelistStr, &server->whitelist);
+}
+
const char*
tr_rpcGetWhitelist (const tr_rpc_server * server)
{
@@ -930,6 +1002,11 @@ tr_rpcGetWhitelistEnabled (const tr_rpc_server * server)
return server->isWhitelistEnabled;
}
+void tr_rpcSetHostWhitelistEnabled(tr_rpc_server* server, bool isEnabled)
+{
+ server->isHostWhitelistEnabled = isEnabled;
+}
+
/****
***** PASSWORD
****/
@@ -1063,6 +1140,28 @@ tr_rpcInit (tr_session * session, tr_variant * settings)
else
tr_rpcSetWhitelistEnabled (s, boolVal);
+ key = TR_KEY_rpc_host_whitelist_enabled;
+
+ if (!tr_variantDictFindBool(settings, key, &boolVal))
+ {
+ missing_settings_key(key);
+ }
+ else
+ {
+ tr_rpcSetHostWhitelistEnabled(s, boolVal);
+ }
+
+ key = TR_KEY_rpc_host_whitelist;
+
+ if (!tr_variantDictFindStr(settings, key, &str, NULL) && str != NULL)
+ {
+ missing_settings_key(key);
+ }
+ else
+ {
+ tr_rpcSetHostWhitelist(s, str);
+ }
+
key = TR_KEY_rpc_authentication_required;
if (!tr_variantDictFindBool (settings, key, &boolVal))
missing_settings_key (key);
diff --git a/libtransmission/rpc-server.h b/libtransmission/rpc-server.h
index e0302c5ea..8c9e6b24e 100644
--- a/libtransmission/rpc-server.h
+++ b/libtransmission/rpc-server.h
@@ -49,6 +49,10 @@ void tr_rpcSetWhitelist (tr_rpc_server * server,
const char* tr_rpcGetWhitelist (const tr_rpc_server * server);
+void tr_rpcSetHostWhitelistEnabled(tr_rpc_server* server, bool isEnabled);
+
+void tr_rpcSetHostWhitelist(tr_rpc_server* server, char const* whitelist);
+
void tr_rpcSetPassword (tr_rpc_server * server,
const char * password);
diff --git a/libtransmission/session.c b/libtransmission/session.c
index 844cadba8..58b717913 100644
--- a/libtransmission/session.c
+++ b/libtransmission/session.c
@@ -359,6 +359,8 @@ tr_sessionGetDefaultSettings (tr_variant * d)
tr_variantDictAddStr (d, TR_KEY_rpc_username, "");
tr_variantDictAddStr (d, TR_KEY_rpc_whitelist, TR_DEFAULT_RPC_WHITELIST);
tr_variantDictAddBool (d, TR_KEY_rpc_whitelist_enabled, true);
+ tr_variantDictAddStr(d, TR_KEY_rpc_host_whitelist, TR_DEFAULT_RPC_HOST_WHITELIST);
+ tr_variantDictAddBool(d, TR_KEY_rpc_host_whitelist_enabled, true);
tr_variantDictAddInt (d, TR_KEY_rpc_port, atoi (TR_DEFAULT_RPC_PORT_STR));
tr_variantDictAddStr (d, TR_KEY_rpc_url, TR_DEFAULT_RPC_URL_STR);
tr_variantDictAddBool (d, TR_KEY_scrape_paused_torrents_enabled, true);
diff --git a/libtransmission/transmission.h b/libtransmission/transmission.h
index 4f76adfd6..e213a8f4e 100644
--- a/libtransmission/transmission.h
+++ b/libtransmission/transmission.h
@@ -123,6 +123,7 @@ const char* tr_getDefaultDownloadDir (void);
#define TR_DEFAULT_BIND_ADDRESS_IPV4 "0.0.0.0"
#define TR_DEFAULT_BIND_ADDRESS_IPV6 "::"
#define TR_DEFAULT_RPC_WHITELIST "127.0.0.1"
+#define TR_DEFAULT_RPC_HOST_WHITELIST ""
#define TR_DEFAULT_RPC_PORT_STR "9091"
#define TR_DEFAULT_RPC_URL_STR "/transmission/"
#define TR_DEFAULT_PEER_PORT_STR "51413"
diff --git a/libtransmission/web.c b/libtransmission/web.c
index ee495e9fc..c7f062730 100644
--- a/libtransmission/web.c
+++ b/libtransmission/web.c
@@ -594,6 +594,7 @@ tr_webGetResponseStr (long code)
case 415: return "Unsupported Media Type";
case 416: return "Requested Range Not Satisfiable";
case 417: return "Expectation Failed";
+ case 421: return "Misdirected Request";
case 500: return "Internal Server Error";
case 501: return "Not Implemented";
case 502: return "Bad Gateway";