[Full-Disclosure] Heap overflow in Mozilla Browser <= 1.7.3 NNTP code.

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Date: Wed, 29 Dec 2004 22:24:21 +0100 (CET)
To: full-disclosure@lists.netsys.com

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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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