People do attack XML parsing (as well as any other input),
the encryption on the wire doesn't stop a malicious client
from crafting special input and sending it to the server.
I did a cursory look at the code and I believe Nick is correct
that the function in question is never called with a user-input
for the format string. Thus, I don't believe this particular
issue is really a vulnerability.
LibXML2 was tested by Coverity (last test from 2018 build):
https://scan.coverity.com/projects/libxml2
It might make sense to upload a fresh build and see what Coverity
finds. Looks like in 2018 it found a few issues (though hard to
say how real are those without deeper look).
Best,
Aleksey
On 10/29/19 3:05 PM, Eric Eberhard wrote:
I agree. I also don’t think people attack XML parsing. The
sending/receiving can be done encrypted. This seems a lot like a
theoretical problem, not a real-world problem.
My feelings are that protecting against all possible attacks is not
possible. Or stupid programming.
Take the physical world. Maybe you just lock your house. Or maybe you
have an alarm system. Or maybe locked gates. Maybe patrolled by
Dobermans. Maybe patrolled by armed guards with machine guns.
My point is – people can pick locks. Defeat alarms. Scale gates. Kill
dogs. Kill guards. It can get silly. Maybe one should make an
underground compound with fingerprint and retina scans as well.
You have to stop it someplace. If this was CIA or FBI or something I’d
go along with the complaint. But most of us use this in a business
setting and we apply *reasonable *security measures, not insanely
overkill measures.
Eric
*From:*xml [mailto:xml-boun...@gnome.org] *On Behalf Of *Webb Scales
*Sent:* Tuesday, October 29, 2019 7:18 AM
*To:* Raphael de Carvalho Muniz <raph...@copin.ufcg.edu.br>
*Cc:* xml@gnome.org
*Subject:* Re: [xml] Research about vulnerabilities
Raphael,
First, the disclaimers: I'm not an XML maintainer or even a
contributor; and, I've only given this a cursory glance.
Here are my reactions.
First, the routine in question is declared to be of module static
scope. I believe that this means that any exploitation of it would have
to be indirect, coming from within LibXML2.
Second, the code appears to properly protect against buffer overflow, so
the only exploitation that I see is the one that you illustrated,
leaking memory position information. However, the function in question
does nothing that its caller could not do -- it calls malloc() and (in
the example you provided) returns the address of what might be a stack
location (although, really, it could be any random junk, I think). By
definition, the caller already knows the stack location, and the caller
certainly has its own access to malloc().
So, I for one, don't see any weakness exposed by the code which you
provided. This doesn't mean that there is no weakness in LibXML2, but,
to find it if it's there, you'll have to interrogate the code which
calls this routine.
Webb
On 10/29/19 9:30 AM, Raphael de Carvalho Muniz wrote:
Dear libxml2 owners,
I am performing research about weaknesses in C open source programs.
As part of my research, I am studying weaknesses that may be
vulnerabilities in the Libxml2 project.
I found in the commit history of Libxml2 (commit 9acef28) the
presence of the following code snippet in the libxml.c file (Lines
1,597 - 1,612). I believe that this commit presents a weakness that,
If format strings can be influenced by an attacker, they can be
exploited. This weakness is characterized by CWE Project as CWE-134:
Use of Externally-Controlled Format String. When an attacker can
modify an externally-controlled format string, this can lead to
buffer overflows, denial of service, or data representation problems.
Moreover, I performed a software testing strategy with respect to
confirm the vulnerability. We provide as input to the char *msg the
value "%xtest" and the function libxml_buildMessage return the
value"fc0c748ex", exposing a memory position.
This is the GitHub link to the commit:
https://github.com/GNOME/libxml2/commit/9acef289285008f81b4b66b4880baf600773cf67
Code snippet:
static char *
libxml_buildMessage(const char *msg, va_list ap){
int chars;
char *str;
str = (char *) xmlMalloc(1000);
if (str == NULL)
return NULL;
chars = vsnprintf(str, 999, msg, ap);
if (chars >= 998)
str[999] = 0;
return str;
}
Looking at this code snippet, I am wondering if you could answer the
following brief questions:
We understand that this code has a weakness. Do you agree?
How do you detect weaknesses? Do you use any tool to detect them?
We would be very grateful if you say to us if you agree, and if you
are going to fix it.
--
Raphael de Carvalho Muniz, M.Sc.
Lattes: http://lattes.cnpq.br/1454914002384966
e-Mail: raphaeld...@gmail.com <mailto:raphaeld...@gmail.com> /
raph...@copin.ufcg.edu.br <mailto:raph...@copin.ufcg.edu.br>
Fone: +55 84 98801 1218
_______________________________________________
xml mailing list, project pagehttp://xmlsoft.org/
xml@gnome.org <mailto:xml@gnome.org>
https://mail.gnome.org/mailman/listinfo/xml
--
Webb Scales
Principal Software Architect
603-673-2306
www.ursasecure.com <https://www.ursasecure.com>
w...@ursasecure.com <mailto:w...@ursasecure.com>
_______________________________________________
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xml@gnome.org
https://mail.gnome.org/mailman/listinfo/xml
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