Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Mon, 10 Dec 2018 19:57:21 +0100
From: Solar Designer <>
To: Pavel Cheremushkin <>
Subject: Re: libvnc and tightvnc vulnerabilities

On Mon, Dec 10, 2018 at 04:08:00PM +0000, Pavel Cheremushkin wrote:
> These particular issues I was describing in my previous letter are located in source code of TightVNC vncviewer. Source code of TightVNC 1.3.10 vncviewer can be acquired though this link and integer overflow that leads to a heap-buffer-overflow I was speaking about is located on the line 1220 inside file `vnc_unixsrc/vncviewer/rfbproto.c`. It is a fun fact that inside `libvncclient/rfbproto.c` the same code is located on line 2220, but all bugs connected with LibVNC I described in Github issues inside LibVNC repository.

Oh.  So you reported the instance of that one issue in LibVNC here:

Upstream's fix appears to be to add casts to (uint64_t) before adding 1
in those many malloc() calls.  On platforms with larger than 32-bit
size_t, this should be sufficient against integer overflows since the
sizes are read from 32-bit protocol fields, but it isn't sufficient to
prevent maliciously large memory allocation on the client by a rogue
server.  On a platform with 32-bit size_t, this isn't even sufficient to
prevent the integer overflows.  If I haven't missed anything, it'd be
great if you open a new issue suggesting introduction of safety limits
prior to those malloc() lines.

The current code is:

  case rfbServerCutText:
    char *buffer;

    if (!ReadFromRFBServer(client, ((char *)&msg) + 1,
			   sz_rfbServerCutTextMsg - 1))
      return FALSE;

    msg.sct.length = rfbClientSwap32IfLE(msg.sct.length);

    buffer = malloc((uint64_t)msg.sct.length+1);

    if (!ReadFromRFBServer(client, buffer, msg.sct.length)) {
      return FALSE;

    buffer[msg.sct.length] = 0;

    if (client->GotXCutText)
      client->GotXCutText(client, buffer, msg.sct.length);



but per the commits referenced in issue #247 above, there are many more
instances of the "malloc(... + 1)" pattern, which were patched similarly



Powered by blists - more mailing lists

Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.