1. Asterisk
  2. ASTERISK-19905

Security Vulnerability: remotely exploitable crash in chan_skinny if client is disconnected when client is not in on-hook state


    • Type: Bug Bug
    • Status: Closed
    • Severity: Blocker Blocker
    • Resolution: Fixed
    • Affects Version/s:, 10.4.0
    • Target Release Version/s:, 10.4.1
    • Component/s: Channels/chan_skinny
    • Security Level: None
    • Labels:
    • Regression:


      Reported by Christoph Hebeisen of Telus Labs.

      Quoting from the vulnerability report:

      "A Null-pointer dereference has been identified in the SCCP (Skinny) channel driver of Asterisk. When an SCCP client closes its connection to the server, a pointer in a structure is set to Null. If the client was not in the on-hook state at the time the connection was closed, this pointer is later dereferenced.

      A remote attacker with a valid SCCP ID can can use this vulnerability by closing a connection to the Asterisk server in certain call states (e.g. "Off hook") to crash the server. Successful exploitation of this vulnerability would result in termination of the server, causing denial of service to legitimate users.

      The following code snippets have been taken from channels/chan_skinny.c as shipped in the source archive of Asterisk 10.5.0-rc1. Comments added by TELUS Security Labs start with the string TSL."

      static int get_input(struct skinnysession *s)
      [ ... Truncated for vulnerability ... ]
       	 } else if (res != 4) {
                       // *TSL* This section is executed when a skinny client closes its connection.
       	 	 ast_log(LOG_WARNING, "Skinny Client sent less data than expected. �Expected 4 but got %d.\n", res);
       	 	 if (res == 0) {
       	 	 	 if (skinnydebug)
       	 	 	 	 ast_verb(1, "Skinny Client was lost, unregistering\n");
       	 	 	 skinny_unregister(NULL, s); � // *TSL* See below
       	 	 return -1;
      static int skinny_unregister(struct skinny_req *req, struct skinnysession *s)
       struct skinny_device *d;
       struct skinny_line *l;
       struct skinny_speeddial *sd;
       d = s->device;
      [ ... Truncated for readability ... ]
       	 	 if (l->device == d) {
       	 	 	 l->device = NULL; � // *TSL* Set device pointer to NULL
       	 	 	 ast_parse_allow_disallow(&l->prefs, l->cap, "all", 0);
       	 	 	 l->instance = 0;
       	 	 	 manager_event(EVENT_FLAG_SYSTEM, "PeerStatus", "ChannelType: Skinny\r\nPeer:
                                  Skinny/%s@%s\r\nPeerStatus: Unregistered\r\n", l->name, d->name);
       	 	 	 ast_devstate_changed(AST_DEVICE_UNAVAILABLE, "Skinny/%s", l->name);
      static void transmit_stop_tone(struct skinny_device *d, int instance, int reference)
       struct skinny_req *req;
       if (!(req = req_alloc(sizeof(struct stop_tone_message), STOP_TONE_MESSAGE)))
       req->data.stoptone.instance = htolel(instance);
       req->data.stoptone.reference = htolel(reference);
       transmit_response(d, req); � // *TSL* If device is unregistered, d is Null
      static void transmit_response(struct skinny_device *d, struct skinny_req *req)
       transmit_response_bysession(d->session, req); � // *TSL* Dereference (crash, first vector)
      static int skinny_indicate(struct ast_channel *ast, int ind, const void *data, size_t datalen)
       struct skinny_subchannel *sub = ast->tech_pvt;
       struct skinny_line *l = sub->line;
       struct skinny_device *d = l->device;
       struct skinnysession *s = d->session; � // *TSL* Dereference (crash, second vector)
       if (!s) {
       	 ast_log(LOG_NOTICE, "Asked to indicate '%s' condition on channel %s, but session does not exist.\n",
                 control2str(ind), ast->name);
       	 return -1;
      1. AST-19905-1.8.diff
        4 kB
        Damien Wedhorn
      2. AST-19905-10.diff
        4 kB
        Damien Wedhorn
      3. AST-19905-trunk.diff
        4 kB
        Damien Wedhorn
      4. AST-2012-008-1.8.diff
        3 kB
        Matt Jordan
      5. AST-2012-008-10.diff
        2 kB
        Matt Jordan
      6. AST-2012-009-10.diff
        0.9 kB
        Matt Jordan
      7. skinny.ldevice-deref.patch
        3 kB
        Damien Wedhorn
      8. skinny.unregister.patch
        2 kB
        Damien Wedhorn
      9. vendor disclosure notes.txt
        13 kB
        Matt Jordan

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          Transition Time In Source Status Execution Times Last Executer Last Execution Date
          Triage Triage Open Open
          2m 4s 1 Matt Jordan 23/May/12 11:33 AM
          Open Open Closed Closed
          6d 2h 4m 1 Digium Subversion 29/May/12 1:37 PM


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