Disable extending to private/internal addresses by default

This is important, since otherwise an attacker can use timing info
to probe the internal network.

Also, add an option (ExtendAllowPrivateAddresses) so that
TestingTorNetwork won't break.

Fix for bug 6710; bugfix on all released versions of Tor.

diff --git a/changes/bug6710 b/changes/bug6710
new file mode 100644 (file)
index 0000000..69a3c7e
--- /dev/null
+++ b/changes/bug6710
@@ -0,0 +1,7 @@
+  o Major bugfixes (security):
+    - Reject any attempt to extend to an internal address. Without
+      this fix, a router could be used to probe addresses on an
+      internal network to see whether they were accepting
+      connections. Fix for bug 6710; bugfix on all released versions
+      of Tor.
+

diff --git a/doc/tor.1.txt b/doc/tor.1.txt
index e7ba8485c0f3401744a08ef5ad54f45a7f3cb80c..7e0751b2b25824fea7527dc236136bdfccea425b 100644 (file)
--- a/doc/tor.1.txt
+++ b/doc/tor.1.txt
@@ -1470,6 +1470,11 @@ is non-zero):
     its extra-info documents that it uploads to the directory authorities.
     (Default: 1)
 
+**ExtendAllowPrivateAddresses** **0**|**1**::
+    When this option is enabled, Tor routers allow EXTEND request to
+    localhost, RFC1918 addresses, and so on. This can create security issues;
+    you should probably leave it off. (Default: 0)
+
 DIRECTORY SERVER OPTIONS
 ------------------------
 
@@ -1795,6 +1800,7 @@ The following options are used for running a testing Tor network.
        ClientRejectInternalAddresses 0
        CountPrivateBandwidth 1
        ExitPolicyRejectPrivate 0
+       ExtendAllowPrivateAddresses 1
        V3AuthVotingInterval 5 minutes
        V3AuthVoteDelay 20 seconds
        V3AuthDistDelay 20 seconds

diff --git a/src/or/circuitbuild.c b/src/or/circuitbuild.c
index 39a223b2f426f7113f5d1a2bb27c14668f5ca862..f11bebf7c9354c6ff84cbd2769c19e6b221f75cd 100644 (file)
--- a/src/or/circuitbuild.c
+++ b/src/or/circuitbuild.c
@@ -2432,6 +2432,13 @@ circuit_extend(cell_t *cell, circuit_t *circ)
     return -1;
   }
 
+  if (tor_addr_is_internal(&n_addr, 0) &&
+      !get_options()->ExtendAllowPrivateAddresses) {
+    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+           "Client asked me to extend to a private address");
+    return -1;
+  }
+
   /* Check if they asked us for 0000..0000. We support using
    * an empty fingerprint for the first hop (e.g. for a bridge relay),
    * but we don't want to let people send us extend cells for empty

diff --git a/src/or/config.c b/src/or/config.c
index 3970808fb30a53b8d37893c9ebcfdede9d787f6a..d5e80cc832856edbc25ce1cf187465cd8b173779 100644 (file)
--- a/src/or/config.c
+++ b/src/or/config.c
@@ -276,6 +276,7 @@ static config_var_t _option_vars[] = {
   V(ExitPolicy,                  LINELIST, NULL),
   V(ExitPolicyRejectPrivate,     BOOL,     "1"),
   V(ExitPortStatistics,          BOOL,     "0"),
+  V(ExtendAllowPrivateAddresses, BOOL,     "0"),
   V(ExtraInfoStatistics,         BOOL,     "1"),
 
 #if defined (WINCE)
@@ -473,6 +474,7 @@ static const config_var_t testing_tor_network_defaults[] = {
   V(ClientRejectInternalAddresses, BOOL,   "0"),
   V(CountPrivateBandwidth,       BOOL,     "1"),
   V(ExitPolicyRejectPrivate,     BOOL,     "0"),
+  V(ExtendAllowPrivateAddresses, BOOL,     "1"),
   V(V3AuthVotingInterval,        INTERVAL, "5 minutes"),
   V(V3AuthVoteDelay,             INTERVAL, "20 seconds"),
   V(V3AuthDistDelay,             INTERVAL, "20 seconds"),

diff --git a/src/or/or.h b/src/or/or.h
index 908daa61c0a471898ea224c0e96bfd8185724494..9074083a0430306a7fe7dcac3f44b0d65f70ef2a 100644 (file)
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -3029,8 +3029,10 @@ typedef struct {
   config_line_t *RecommendedVersions;
   config_line_t *RecommendedClientVersions;
   config_line_t *RecommendedServerVersions;
-  /** Whether dirservers refuse router descriptors with private IPs. */
+  /** Whether dirservers allow router descriptors with private IPs. */
   int DirAllowPrivateAddresses;
+  /** Whether routers accept EXTEND cells to routers with private IPs. */
+  int ExtendAllowPrivateAddresses;
   char *User; /**< Name of user to run Tor as. */
   char *Group; /**< Name of group to run Tor as. */
   config_line_t *ORPort_lines; /**< Ports to listen on for OR connections. */