bugtraq - Multiple vulnerabilities in SheerDNS

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Date: Sun, 13 Apr 2003 18:00:13 +0200
From: Jedi/Sector One <j@...eftpd.org>
To: bugtraq@...urityfocus.com
Subject: Multiple vulnerabilities in SheerDNS

Date    : 04/13/2003
Product : SheerDNS
Author  : Frank Denis <j@...eftpd.org>

   ------------------------[ Product description ]------------------------

  SheerDNS was written to be a simple replacement master DNS server that can
be used where atomic updates are required. Because it stores each record in
a small file, updating records does not require the sheerdns process to be
notified or restarted. Each update is immediately available and served as-is. 

  SheerDNS is extremely light-weight, simple, and fast, and written with
security in mind. 

  Home page : http://threading.2038bug.com/sheerdns/

     ------------------------[ Vulnerabilities ]------------------------

  Two main vulnerabilities were found in SheerDNS 1.0.0 .

 * Buffer overflow in CNAME handling.

  There's buffer overflow in the way SheerDNS constructs a reply when
answering a CNAME request. See line 385 of sheerdns.c :

  strcpy ((char *) query, lookup_results[0]);

  query is a 256 bytes buffer on the stack, while lookup_results[0] can be
up to 1024 bytes (see dir.c) .

  Lookup results are read from local files, hopefully created by trusted
processes. However, a second vulnerability can break this.

 * Directory traversal in directory_lookup().

  The point in SheerDNS is that data is directly served from files. Thus, a
request for the <type> record of the <zone> zone results in reading a file
whoose location is :

  /var/sheerdns/<zone>/<type>

  However, SheerDNS 1.0.0 doesn't sanitize the requested zone.

  Using a specially crafted DNS request, an arbitrary directory can be read,
moreover SheerDNS needs root privileges and doesn't chroot.

  The attached proof-of-concept makes it read the /tmp/passwd/ directory.

 * If an untrusted user can create files with arbitrary names on a server
running SheerDNS, both vulnerabilities can be combined. SheerDNS can be
forced to read any untrusted file whoose name is "CNAME" and whoose content
will trigger the query[] buffer overflow.

    ------------------------[ Affected versions ]------------------------

  Both vulnerabilities have been confirmed on SheerDNS 1.0.0 .

 ------------------------[ Vendor status and fixes ]------------------------

  SheerDNS author Paul Sheer addressed these vulnerabilities the day they
were reported, among with some other problems.

  SheerDNS 1.0.1 is now available for download from the project's main site.

-- 
 __  /*-      Frank DENIS (Jedi/Sector One) <j@...Networks.Com>     -*\  __
 \ '/    <a href="http://www.PureFTPd.Org/"> Secure FTP Server </a>    \' /
  \/  <a href="http://www.Jedi.Claranet.Fr/"> Misc. free software </a>  \/

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