[UNIX] Remote Vulnerabilties in mod_ntlm
From: support@securiteam.com
Date: 04/21/03
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From: support@securiteam.com To: list@securiteam.com Date: 21 Apr 2003 21:00:38 +0200
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Remote Vulnerabilties in mod_ntlm
------------------------------------------------------------------------
SUMMARY
<http://www.sourceforge.net/projects/modntlm> mod_ntlm is an Apache
module (originally designed for Apache 1.3, now available for Apache 2.0)
that provides the ability for Apache services to authenticate users via
the NTLM authentication technology that is largely specific to Microsoft
IIS.
The module has been found to contain a pair of remotely exploitable
vulnerabilities that would allow attacker to cause the server to execute
arbitrary code.
DETAILS
Vulnerable systems:
* Apache 1.3: mod_ntlm v0.4 and prior
* Apache 2.0: mod_ntlmv2 v0.1
mod_ntlm contains a pair of remotely exploitable vulnerabilities in its
data logging routine. The vulnerabilities occur in a default build. The
mod_ntlm "log()" function contains a pair of exploitable error conditions:
static void
log(const request_rec * r, const char *format,...)
{
va_list ap;
char *s;
if ((s = (char *) malloc(2048)) == NULL)
return;
va_start(ap, format);
vsprintf(s, format, ap);
va_end(ap);
ap_log_rerror(APLOG_MARK, APLOG_NOERRNO | APLOG_NOTICE, r, s);
free(s);
}
The function is called with user-supplied input in various locations in
the code. The first vulnerability is a heap overflow -- if any
user-supplied input is greater than 2048 characters, memory management
structures are overwritten, and arbitrary code execution is possible.
Secondly, an incorrect call to ap_log_rerror(). The last parameter to
ap_log_rerror() is not a log line, but a format string. Due to the
previous decoding operation, it becomes possible to pass format specifiers
to ap_log_rerror(). A carefully crafted format string may allow code
execution.
Proof-of-Concept:
Either of the following two sessions will cause httpd to exit due to
segmentation fault:
GET / HTTP/1.0
Authorization: [Ax3000]
Or
GET / HTTP/1.0
Authorization: %n%n%n%n
Similarly, a proxy server can be exploited by using an external URL
(http://www.yahoo.com/, for instance), in place of "/", and using
Proxy-Authorization, in place of Authorization in the examples above.
Vendor Status:
The vulnerability was submitted to the vendor via SourceForge at:
<http://sourceforge.net/tracker/index.php?func=detail&aid=723468&group_id=4906&atid=104906> http://sourceforge.net/tracker/index.php?func=detail&aid=723468&group_id=4906&atid=104906
The vendor has not responded to the bug report as of the time of writing
of this advisory.
ADDITIONAL INFORMATION
The information has been provided by <mailto:mattmurphy@kc.rr.com>
Matthew Murphy.
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