Linux nfs-utils xlog() off-by-one bug

[Janusz Niewiadomski <funkysh () isec pl>]

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Synopsis:       Linux nfs-utils xlog() off-by-one bug 
Product:        nfs-utils
Version:        <= 1.0.3
Vendor:         http://sourceforge.net/projects/nfs/

URL:            http://isec.pl/vulnerabilities/
CVE:            CAN-2003-0252
Author:         Janusz Niewiadomski <funkysh () isec pl>
Date:           July 14, 2003


Issue:
======

Linux NFS utils package contains remotely exploitable off-by-one bug.
A local or remote attacker could exploit this vulnerability by sending 
specially crafted request to rpc.mountd daemon.


Details:
========

An off-by-one bug exist in xlog() function which handles logging of 
requests. An overflow occurs when function is trying to add missing
trailing newline character to logged string. 

Due to miscalculation, if a string passed to the functions is equal
or longer than 1023 bytes, the '\0' byte will be written beyond the 
buffer:
  

- ------8<------cut-here------8<------

        char            buff[1024];
        ...
 
        va_start(args, fmt);
        vsnprintf(buff, sizeof (buff), fmt, args);
        va_end(args);
        buff[sizeof (buff) - 1] = 0;

        if ((n = strlen(buff)) > 0 && buff[n-1] != '\n') {
                buff[n++] = '\n'; buff[n++] = '\0';
        }

- ------8<------cut-here------8<------


Impact:
=======

Local or remote attacker which is capable to send RPC request to
vulnerable mountd daemon could execute artitrary code or cause
denial of service.


Status:
=======

Vendor has been notified on June 10, 2003. The fix is incorporated
in recent 1.0.4 release of nfs-utils.

The Mitre Corp.'s Common Vulnerabilities and Exposures (CVE) Project
has assigned the identification number CAN-2003-0252 to this issue.


- -- 
Janusz Niewiadomski
iSEC Security Research
http://isec.pl/

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