___ Summary __________________________________________________________
Title: Directory traversal vulnerability in sendform.cgi
Date: July 30, 2002
Author: Steve Christey (coleyat_private)
Credits: Brian Caswell (bmcat_private)
Erik Tayler (erikat_private)
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 (vulnhelpat_private) 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 (bmcat_private). 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 ______________________________________________________________
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