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The Problem with Signature-based Web App Security

Posted: January 29th, 2015 | Filed under: IIS & HTTP

In the real world we have the benefit of being present and able to see and analyze scenarios in real-time. In the cyber world, we rely on code and algorithms to handle millions of complex tasks every day without much real-time human intervention. Unfortunately, one of the tasks that we leave in the hands of technology is web security.

This is a problem because unlike humans, code and algorithms cannot decide what is good and bad. Not from a philosophical moral perspective (humans still struggle with that), but from a security standpoint. In order for web security tools to know if a user is doing something bad it needs to be programmed to know what specifically to look for. The way that many tools know how to detect malicious actions or activity it by using attack/threat signatures. This may make for a great business model for those who sell such products, since they can sell signature updates, etc, but it makes for a dangerous security model.

What are signatures, anyway?

So what are signature-based rules, exactly? One way to envision them are as a glossary of different threats that a security tool can reference to know whether or not it should take action against inputs. A signature is typically based on an exploit that has already occurred and has been documented. The signature details the way that the exploit works using a series of parameters to indicate the specific actions that occur during the exploit.

This model depends on matching inputs to a specific signature in order to block them. This can be likened to taking a fingerprint of someone who wants access to something and comparing it against a database of fingerprints of known criminals. This will work great for stopping frequent criminals, but will never stop the first-time offenders.

Example rule:
'Cross-site Scripting (XSS) Attack',id:'958016',tag:'OWASP_CRS/WEB_ATTACK/XSS',tag:'WASCTC/WASC-8',tag:'WASCTC/WASC-22',tag:'OWASP_TOP_10/A2',tag:'OWASP_AppSensor/IE1',tag:'PCI/6.5.1',logdata:'Matched Data: %{TX.0} found within %{MATCHED_VAR_NAME}: %{MATCHED_VAR}',severity:'2',setvar:'tx.msg=%{rule.msg}',setvar:tx.xss_score=+%{tx.critical_anomaly_score},setvar:tx.anomaly_score=+%{tx.critical_anomaly_score},setvar:tx.%{}-OWASP_CRS/WEB_ATTACK/XSS-%{matched_var_name}=%{tx.0}"

The problem with security tools that rely on fingerprint matching is that fingerprints are unique, and the fingerprints for attacks that haven’t happened yet don’t exist. That leaves a gaping hole in these tools ability to provide security.

Good luck stopping zero-days!

Since signatures only account for what has already been seen, they don’t do anything to account for what has yet to be seen. When a new, never-before-seen, zero day comes along the tool won’t find any matches in the signature database. Only after the exploit has been observed in the wild will vendors update their signature lists and send out an update to customers, who then typically need to add the update.

Yes, protecting against the known vulnerabilities that many script kiddies will try is indeed valuable. However, the script kiddies don’t pose the same threat as a well-trained hacker or even a hacker who possesses knowledge of a zero day vulnerability. Without any protection against new or unseen attacks, signature-based tools leave a wide attack surface that needs to be accounted for another way.

Signatures Everywhere!

Many organizations use automated security scanners to find vulnerabilities in their apps, and in turn can update their WAFs with the information learned from the scanner. So if the scan finds vulnerability ABC, then the security rules for that vulnerability can be automatically for the WAF to import (this isn’t the case with every tool, but is a feature than many tools highlight). The problem is that the scanner is using heuristics to find the vulnerabilities in the first place. Herein lies the vicious circle of signature-based security and the illusion of security.


Vulnerability scan run with signature-based tool > Rules created from scan > Rules imported into security tool > New scan rules released, prompting rescan >


With this type of system in place, you’re never really achieving protection against anything other than known vulnerabilities. It’s like basing all flight security off of the do-not-fly list, but not knowing you can/should stop the person with a dangerous looking item for – at the least – a further inspection.

Another issue with this approach is the constant need to update the rules. Not only does your security depend on a rule existing, but it also depends on you updating the rules (unless rules update automatically) immediately upon release. A breach could come down to: no rules existing to stop an exploit, or you not updating the rules in a timely manner.

A different approach

There are alternative ways to approach web application security, and not all vendors are using a signature-based model. Port80 Software takes an algorithmic and behavioral-based approach that combines whitelists and blacklists and completely ditches the signature model.

The signature approach is so common that when people come to evaluate our Web application firewall, ServerDefender, they often are confused by its non-use of signatures. People often ask, “Well, if it doesn’t use signatures, then how is it providing protection?” and “How often do you update signatures? And are they free?”

There are indeed alternative ways to approach web application security, and not all vendors are using a signature-based model. Port80 Software takes an algorithmic and behavioral-based approach that combines whitelists and blacklists and completely ditches the signature model.

Curious to see what our approach is? Learn about our innovative – signature-free – approach to application security.

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Exploring the LogViewer in ServerDefender VP

Posted: November 15th, 2014 | Filed under: IIS & HTTP, Web and Application Security | Tags: , , , , , ,

Security You Can See

For the least few years, we have been developing ServerDefender VP, an advanced Web application firewall for IIS. One of the features that has been evolving along with ServerDefender VP is the LogViewer. This is the hub of the WAF where users can interact with and monitor malicious traffic hitting their site. Since there is so much to do within the LogViewer it sometimes becomes easy for a feature or two to be missed, so we’ve decided to explain some of the cool tricks its capable of.

What is the LogViewer?

The LogViewer is a tool that visualizes events (blocked threats and errors) that occur in your application and allows you take a variety of different actions on them with only a few clicks. When selecting an event users can see an array of data that pertains to it such as the referrer, user-agent, IP address, session ID, GET and POST data, and other critical information.

ServerDefender VP Web app firewall LogViewer

Click to enlarge.

What Can Actions Can I take on an Event?

There are several different actions that a user can take on an event in the LogViewer. The primary actions are for security settings (blocking IP addresses and creating exceptions), forensic tools (viewing all events by IP, comparing a session against IIS logs), and exporting reports.

ServerDefender VP LogViewer Actions

Click to enlarge.

Adding Exceptions

One of the key actions available to users from the LogViewer is the ability to add an exception to event, such as a false positive. Adding an exception on an event lets users specify new settings should the same event occur. This means that users can tell a blocked action to be allowed and configure new rules for the future.

ServerDefender VP Input Exception

Click to enlarge.


The LogViewer’s forensic tools enable users to gain further knowledge about an event and the session and IP behind it.

“View This Session in IIS Logs” displays the session logs with errors recorded by ServerDefender VP highlighted. This feature is useful to determine what occurred in a session prior to an error occurring and establishing the validity of an error, should there be any questions around it.

“View this IP Only” displays only the events in the LogViewer attributed to that IP address. This makes it easier to visualize the actions of a single IP address and understand its patterns, which can help users determine if the action they should take against the IP, if any.

Questions for Us? Ready to try?

The LogViewer is a powerful tool for viewing malicious traffic in your app and way to quickly react to events. If there’s anything else you’d like to learn about the LogViewer – or ServerDefender VP in general –  send us an email at or Tweet us @port80software. If you’d like to enjoy a 30-day free trial, go ahead and download now.

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Patch Now: Schannel Vulnerability Poses Huge Threat

Posted: November 13th, 2014 | Filed under: IIS & HTTP

A critical vulnerability in Microsoft Schannel headlined the security bulletin released by Microsoft for November. The vulnerability is the latest in TLS vulnerabilities for 2014, and means that every major TLS stack has been impacted by a severe vulnerability this year alone, as reported by Ars Technica. The Schannel vulnerability is drawing comparisons to Heartbleed, as it similarly allows for remote code execution and data theft.

Needless to say, it is imperative that affected systems are patched immediately.

Microsoft Security Bulletin MS14-066 – Critical – Find & Install Patch

Secure Channel, also known as Schannel, is the standard security package used by SSL/TLS in Windows. The Schannel vulnerability impacts all versions of Windows dating back to Vista/Windows Server 2003.

After the Bash and Poodle Vulnerabilities earlier this year, we should not be surprised to see a vulnerability that has gone unpatched for an extended period of time. This vulnerability just underscores the fact that even very mature software may have serious bugs from time to time.

The complete November security bulletin can viewed here.

Looking for more details about the Schannel vulnerability (MS14-066)? Read More

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POODLE SSL 3.0 Vulnerability: What it is and how to deal with it

Posted: October 17th, 2014 | Filed under: IIS & HTTP


from our friends at Net-Square

A Vulnerability known as POODLE, an acronym for Padding Oracle On Downgraded Legacy Encryption, is making headlines this week. The bug is a vulnerability in the design of SSL version 3.0, which is more than 15 years. However, SSL 3.0 is still widely supported, and nearly 97% of SSL servers are likely to be vulnerable to the bug, according to an October Netcraft Survey.

SSL v3.0 Vulnerable Servers


This vulnerability allows an attacker to intercept plaintext data from secure connections. Since SSLv3 has been quiet famous in the last 15 years it has put literally millions of browsers in jeopardy. As the chart above indicates, this is a vulnerability that has a sweeping impact.

How it happens?

Though users are upgrading to latest SSL versions (TLS 1.0, 1.1, 1.2), many TLS versions are backward compatible with SSL 3.0, hence when web browsers fail at connecting on these newer SSL version (i.e. TLS 1.0, 1.1, or 1.2), they may fall back to the older SSL 3.0 connection for a smooth user experience.

The other possibility is, a user is forced to step down to SSL 3.0. If an attacker has successfully performed a Man In The Middle attack MITM and causes connection failures, including the failure of TLS 1.0/1.1/1.2 connections. They can force the use of SSL 3.0 and then exploit the poodle bug in order to decrypt secure content transmitted between a server and a browser. Due to this down shift of the protocol the connection becomes vulnerable to the attack, eventually exploiting and intercepting user’s private data.

Google’s Bodo Möller, Thai Duong, and Krzysztof Kotowicz published the complete security advisory which can be found on

Possible remediation

To avoid falling prey to attackers exploiting POODLE, avoiding the use of public Wi-Fi hotspots, if user is sending valuable information (using online banking, accessing social networks via a browser, etc.), and noting this is always a risk, but the Poodle vulnerability makes it even more dangerous.

The other recommendation is disabling SSL v3 and all previous versions of the protocol in your browser settings and also on the server side will completely avoid it.  SSL v3 is 15 years old now and has been superseded by the more up-to-date and widely supported TSL protocol, supported by most modern web browsers.

DigitCert published a detailed step-by-step guide for disabling SSL 3.0.

Richard Burte also shared the command lines to disable SSL 3.0 on GitHub.

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Zero-Day Vulnerability (CVE-2014-4114) in Windows Server Exploited by Russian Espionage Group “Sandworm”

Posted: October 14th, 2014 | Filed under: IIS & HTTP, Web and Application Security


A Russian espionage group is exploiting a zero-day vulnerability in Windows Server 2008 and 2012, iSIGHT Partners reported on Tuesday. Microsoft is currently working on a patch for the vulnerability (CVE-2014-4114), but a number of targets have already been hit.

When exploited, this vulnerability allows an attacker to remotely execute arbitrary code, but requires a specially crafted file and use of social engineering to convince a user to open the file. iSIGHT noted specifically that PowerPoint files were used to exploit the vulnerability.

While there are specific targets that have been named, iSIGHT is also quick to point out that the visibility of the attack is limited and there is potential for broader targeting beyond this group of targets. The known targets include:

  • NATO
  • Ukranian government organizations
  • A Western European government organization
  • Energy sector firms (specifically in Poland)
  • European telecommunications firms
  • An United States academic organization

The team behind the attacks was dubbed the “Sandworm Team,” based on encoded references in command and control URLs and malware samples that refer to the sci-fi series Dune. iSIGHT reported that it has been monitoring the Sandworm Team since late 2013, and believes they were formed sometime in 2009.

Geopolitical Tensions Creating Targets

The takeaway here seems to be that the attacks do not only target governmental entities. The Sandworm Team has instead targeted entities that are geopolitically relevant in a broader sense: energy, telecommunications, education.

This should serve as a sign of potential threats to come. Private sector businesses that are strategically sensitive in a geopolitical sense might be on some state’s list of targets. This means organizations that share information with, provide services to, or provide infrastructure utilized by governmental organizations may be at risk. State-sponsored attacks will focus on targets with strategic significance which can range from obvious ones like power grids and financial institutions to less obvious targets like research universities.

State-sponsored attacks are on the rise and the targets are becoming broader. Organizations who align themselves with sensitive entities should have a heightened sense of awareness and look to raise their defenses if needed.

We will update this post accordingly as the story continues to develop.

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