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Heap overflow in Mozilla Browser <= 1.7.3 NNTP code.
From: Maurycy Prodeus <z33d () isec pl>
Date: Wed, 29 Dec 2004 22:29:27 +0100 (CET)

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Synopsis:  Heap overflow in Mozilla Browser <= 1.7.3 NNTP code.
Product:   Mozilla Browser
Version:   <= 1.7.3
Vendor:    http://www.mozilla.org/
URL:       http://isec.pl/vulnerabilities/isec-0020-mozilla.txt
CVE:       not assigned
Author:    Maurycy Prodeus <z33d () isec pl>
Date:      Dec 29, 2004



Issue:
======

A critical security vulnerability has been found in Mozilla Project code
handling NNTP protocol.


Details:
========

Mozilla browser supports NNTP urls. Remote side is able to trigger  news://
connection to any server. I found a flaw in NNTP handling code which may
cause heap overflow and allow remote attacker to execute arbitrary code on
client machine.

Bugus function from nsNNTPProtocol.cpp:

char *MSG_UnEscapeSearchUrl (const char *commandSpecificData)
329 {
330     char *result = (char*) PR_Malloc (PL_strlen(commandSpecificData) + 1);
331     if (result)
332     {
333         char *resultPtr = result;
334         while (1)
335         {
336             char ch = *commandSpecificData++;
337             if (!ch)
338                 break;
339             if (ch == '\\')
340             {
341                 char scratchBuf[3];
342                 scratchBuf[0] = (char) *commandSpecificData++;
343                 scratchBuf[1] = (char) *commandSpecificData++;
344                 scratchBuf[2] = '\0';
345                 int accum = 0;
346                 PR_sscanf(scratchBuf, "%X", &accum);
347                 *resultPtr++ = (char) accum;
348             }
349             else
350                 *resultPtr++ = ch;
351         }
352         *resultPtr = '\0';
353     }
354     return result;
355 }

When commandSpecificData points to last (next is NULL) character which
is '\\' copying loop may omit termination of source char array and overflow
result buffer.


Affected Versions
=================

Mozilla Browser <= 1.7.3 with mozilla-mail

Solution
=========

This bug is fixed in Mozilla 1.7.5. (Bug 264388)
Mozilla developer Dan Veditz claims that it cannot be exploitable:
"A '\' on the end will certainly trash memory, but at that point you're no
longer reading attacker-supplied data;".

On my RedHat 9.0 with Mozilla 1.7.3 attached proof of concept code
overflows the buffer using attacker-supplied data. I decided to make this
bug public because Mozilla Team hasn't warned users.


Exploitation
============

I have attached proof of concept HTML file which causes heap corruption
and crashes Mozilla 1.7.3 browser (with mozilla-mail). News server must be
existing and available.


- --
Maurycy Prodeus
iSEC Security Research
http://isec.pl/
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Attachment: nntp_crash.txt
Description: PoC


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