Directory traversal vulnerability in sendform.cgi

["Steven M. Christey" <coley () linus mitre org>]

___ Summary __________________________________________________________

       Title: Directory traversal vulnerability in sendform.cgi
        Date: July 30, 2002
      Author: Steve Christey (coley () mitre org)
     Credits: Brian Caswell (bmc () mitre org)
              Erik Tayler (erik () DIGITALDEFENSE NET)
      Vendor: Rod Clark
     Product: sendform.cgi
 Product URL: http://www.scn.org/~bb615/scripts/sendform.html
 OS/Platform: Unix
    Versions: All versions 1.4.4 and earlier, primarily before 1.4
      Impact: Remote unauthenticated attackers can read arbitrary files
              with the privileges of the web server.
        Risk: High
    Solution: Upgrade to v1.45.  A workaround is available, but it
              reduces functionality.
 Identifiers: CVE (CAN-2002-0710), Bugtraq ID (5286)


___ Introduction _____________________________________________________

  Rod Clark's sendform.cgi is a CGI program that reads form data and
  sends it to a program-specified administrator.  An optional
  capability can send additional "blurb files" to the e-mail address
  that is provided in the form.

  Unfortunately, any remote attacker can use sendform.cgi to read
  arbitrary files with the privileges of the web server by modifying
  the BlurbFilePath parameter to reference the desired files.


___ Details __________________________________________________________

  When sendform.cgi is used to notify a user that their form has been
  submitted, it can read "blurb files" from the web server and send
  them in an email to the user.  A remote attacker can manipulate the
  BlurbFilePath parameter to identify any target file (or set of
  files) on the web server, such as /etc/passwd.  The "email"
  parameter can then be modified to point to the attacker's own email
  address, and the SendCopyToUser parameter set to "yes."  When the
  attacker submits the full request to sendform.cgi, a copy of the
  target file will be sent to the attacker.  There may be alternate
  attack vectors that do not require the SendCopyToUser parameter.

  If the attacker can write files to the web server running
  sendform.cgi, then the attacker can fully control the content of the
  e-mail message and send it to arbitrary e-mail addresses.  Since
  other form fields such as the subject line are under attacker
  control, sendform.cgi could then be used as a "spam proxy," in a
  fashion similar to the well-known vulnerability in formmail.pl [1].

  The filename that is provided to BlurbFilePath does not have to
  contain .. characters to escape the web root.  An absolute pathname
  will also work.  Since sendform.cgi only allows a small range of
  characters, plus the .. and /, the attacker can not execute commands
  via shell metacharacters, or redirect output to other files.

  It should be noted that there appear to be multiple programs named
  "sendform.cgi," including custom CGI scripts, which are unrelated to
  the product being discussed in this advisory.


___ Solution _________________________________________________________

  Upgrade to the current version, found at:

  http://www.scn.org/~bb615/scripts/sendform.html

  The only feasible workaround is to disable the Blurb File feature by
  commenting out calls to the functions MailFirstBlurbFile() and
  MailOtherBlurbFiles().

  Thanks to Rod Clark for diligently addressing this vulnerability.


___ Vulnerability Identifiers ________________________________________

  The Common Vulnerabilities and Exposures (CVE) project has assigned
  the name CAN-2002-0710 [2] to this issue. This is a candidate for
  inclusion in the CVE list (http://cve.mitre.org), which standardizes
  names for security problems.

  The SecurityFocus VulnHelp team (vulnhelp () securityfocus com) has
  assigned Bugtraq ID 5286 [3] to this issue.


___ Disclosure Policy ________________________________________________

  Disclosure of this vulnerability has been conducted in accordance
  with the "Responsible Vulnerability Disclosure Process" draft,
  currently published at:

  http://www.ietf.org/internet-drafts/draft-christey-wysopal-vuln-disclosure-00.txt


___ Disclosure History _______________________________________________

  2002/05/10: initial discovery of suspicious code
  2002/05/16: vulnerability verified
  2002/05/16: initial notification to vendor
  2002/05/16: vendor acknowledges receipt
  2002/06/14: vendor updated web site with patched version for review
  2002/06/17: tested patched version, made some recommendations
  2002/06/24: beginning of vacation, sweet vacation
  2002/07/15: vendor provides most recent version
  2002/07/18: final suggestions to vendor (tiny hole still left)
  2002/07/18: CVE candidate obtained
  2002/07/20: vendor releases final version
  2002/07/23: Bugtraq ID obtained
  2002/07/23: final version verified
  2002/07/30: advisory released

  This vulnerability was originally discovered while researching a
  Snort IDS signature with Brian Caswell (bmc () mitre org).  The
  signature apparently originated from a post to the Vuln-Dev mailing
  list on January 24, 2001, by Erik Tayler [4], who inquired about
  directory traversal attacks on sendform.

  Approximately 5 hours were spent researching the vulnerability.  An
  additional 10-15 hours were spent consulting with the vendor and
  evaluating patches.


___ References _______________________________________________________

  [1] http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2001-0357

  [2] http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2002-0710

  [3] http://www.securityfocus.com/bid/5286
  
  [4] http://marc.theaimsgroup.com/?l=vuln-dev&m=98039690620489&w=2


___ EOF ______________________________________________________________