• In which an exposition of Twelve Web (In)Security Truths begins.

    #1 – Software execution is less secure than software design, but running code has more users.

    A site you send people to visit is infinitely more useable than the one you describe to people. (Value differs from usability. Before social media flamed you could raise $41 million dollars on a slide deck.) Talk all you want, but eventually someone wants you to deliver.

    Sure, you could describe Twitter as a glorified event loop around an echo server. You might even replicate it in a weekend with a few dozen lines of Python or Node.js and an EC2 instance. Just try scaling that napkin design to a few hundred million users while keeping security and privacy controls in place. That’s a testament to implementing a complex design. (Or scaling a simple design if you boil it down to sending and receiving tweets.)

    It’s possible to attain impressive security through careful design. A prominent example in cryptography is the “perfect secrecy”1 of the One-Time Pad (OTP). The first OTP appeared in 1882, designed in an era without the codified information theory or cryptanalysis of Claude Shannon and Alan Turing.2 Never the less, its design understood the threats to confidential communications when telegraphs and Morse code carried secrets instead of fiber optics and TCP/IP. Sadly, good designs are sometimes forgotten or their importance unrecognized. The OTP didn’t gain popular usage until its re-invention in 1917, along with a more rigorous proof of its security.

    But security also suffers when design becomes implementation. The OTP fails miserably should a pad be reused or is insufficiently random. The pad must be as long as the input to be ciphered. So, if you’re able to securely distribute a pad (remember, the pad must be unknown to the attacker), then why not just distribute the original message? Once someone introduces a shortcut in the name of efficiency or cleverness the security breaks. (Remember the Debian OpenSSL debacle?) This is why it’s important to understand the reasons for a design rather than treat it as a logic table to be condensed like the singularity of a black hole. Otherwise, you might as well use two rounds of ROT13.

    Web security has its design successes. Prepared statements are a prime example of a programming pattern that should have relegated SQL injection to the CVE graveyard. Avoiding it is inexcusable. Only devotees of Advanced Persistent Ignorance continue to blithely glue SQL statements together with string concatenation. SQL injection is so well-known (at least by hackers) and studied that a venerable tool like sqlmap has been refining exploitation for over six years. The X-Frame-Options header is another example of design that could dispatch a whole class of vulnerabilities (i.e. clickjacking).

    O, but how the Internet loves to re-invent vulns. Whether or not SQL injection is in its death throes, NoSQL injection promises to reanimate its bloated corpse. Herbet West would be proud.

    Sometimes software repeats the mistakes of other projects without considering or acknowledging the reasons for those mistakes. The Ruby on Rails Mass Assignment feature is reminiscent of PHP’s register_globals issues. Both PHP and Ruby On Rails are Open Source projects with large communities. It’s unfair to label the entire group as ignorant of security. But the question of priorities has to be considered. Do you have a default stance of high or low security? Do you have language features whose behavior changes based on configuration settings outside the developer’s control, or that always have predictable behavior?

    Secure design isn’t always easy. Apache’s reverse proxy/mod_rewrite bug went through a few iterations and several months of discussion before Apache developers arrived at an effective solution. Once again, you might argue that the problem lies with users (i.e. poor rewrite rules that omit a path component) rather than the software. Still, the vuln proved how difficult it is to refine security for complex situations.

    HTML injection is another bugbear of web security. (Which makes SQL injection the owlbear?) There’s no equivalent to prepared statements for building HTML on the fly; developers must create solutions for their programming language and web architecture. That doesn’t mean XSS isn’t preventable, prevention just takes more effort and more attention to the context where user-influenced data shows up in a page. Today’s robust JavaScript frameworks help developers avoid many of the XSS problems that arise from haphazard construction of HTML on the server.

    There’s hope on the horizon for countering HTML injection with design principles that are tied to HTTP Headers rather than a particular programming language or web framework. The Content Security Policy (CSP) has moved from a Mozilla effort to a standard for all browsers. CSP won’t prevent HTML injection from occurring, but it will diminish its exploitability because developers will be able to give browsers directives that prevent script execution, form submission, and more. CSP even has the helpful design feature of a monitor or enforce mode, thereby easing the transition to a possibly complex policy.

    Design is how we send whole groups of vulns to the graveyard. Good security models understand the threats a design counters as well as those it does not. Spend too much time on design and the site will never be implemented. Spend too much time on piecemeal security and you risk blocking obscure exploits rather than fundamental threats.

    As the ancient Fremen saying goes, “Truth suffers from too much analysis.”3 So too does design suffer in the face of scrutiny based on unspecific or unreasonable threats. It’s important to question the reasons behind a design and the security claims it makes. Sure, HSTS relies on the frail security of DNS. Yet HSTS is a significant improvement to HTTPS, which in turn is unquestionably better than HTTP. But if you refuse to implement an imperfect solution in favor of preserving the status quo of HTTP then you haven’t done enough consideration of the benefits of encryption.

    Nor are security checklists absolute. The httponly attribute prevents no vulnerabilities. It only prevents JavaScript from accessing a cookie. Blindly following the mantra that httponly must exist on all cookies ignores useful designs where JavaScript intentionally reads and writes cookie values. If you’ve put sensitive data into a Local Storage object, then an XSS vuln is going to expose all that tasty data to a hacker who cares little for the cookie’s accessibility.

    Design your way to a secure concept, code your way to a secure site. When vulnerabilities arise determine if they’re due to flaws in the design or mistakes in programming. A design that anticipates vulnerabilities (e.g. parameterized queries) should make it easy to fix inevitable bugs. Vulnerabilities that surprise developers should lead to design changes that provide more flexibility for resolving the problem. Inflexibility, whether in design or in code, is dangerous to security. Just like the Bene Gesserit say, “Any road followed precisely to its end leads precisely nowhere.”4

    1. In the sense of Claude Shannon’s “Communication Theory of Secrecy Systems”. 

    2.  As Steven Bellovin notes in his paper, an 1882 codebook contains an amusingly familiar phrase regarding identity questions, “Identity can be established if the party will answer that his or her mother’s maiden name is…“ It seems identity proofs haven’t changed in 130 years! 

    3. Frank Herbert. Dune Messiah. p. 81. 

    4. Frank Herbert. Dune. p. 69. 

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  • My current writing project has taken time away from adding new content lately. Here’s a brief interlude of The Twelve Web Security Truths I’ve been toying with as a side project. They are modeled on The Twelve Networking Truths from RFC 1925.

    1. Software execution is less secure than software design, but executing code attracts actual users.
    2. The time saved by not using parameterized queries to build SQL statements should be used to read about using parameterized queries.
    3. Same Origin Policy restricts the DOM access and JavaScript behavior of content loaded from multiple origins. Malware only cares about plugin and browser versions.
    4. Content with XSS vulns are affected by the Same Origin Policy, which is nice for XSS attacks that inject into the site’s origin.
    5. CSRF countermeasures like Origin headers mitigate CSRF, not XSS. Just like X-Frame-Options mitigates clickjacking, not XSS.
    6. Making data safe for serialization with JSON does not make the data safe for the site.
    7. There are four HTML injection vulns in your site today. Hackers will find two of them, the security team will find one, the dev team will introduce another one tomorrow.
    8. Deny lists miss the attack payload that works.
    9. A site that secures user data still needs to work on the privacy of user data.
    10. Hashing passwords with 1,000-round PBKDF2 increases the work factor to brute force the login page by a factor of 1. Increasing this to a 10,000-round PBKDF2 scheme provides an additional increase by a factor of 1.
    11. The vulnerabilities in “web 2.0” sites occur against the same HTML and JavaScript capabilities of “web 1.0” sites. HTML5 makes this different in the same way.
    12. A site is secure when a compromise can be detected, defined, and fixed with minimal effort and users are notified about it.
    13. Off-by-one errors only happen in C.
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  • The biggest threat to modern web applications is someone who exhibits Advanced Persistent Ignorance. Developers rely on all sorts of APIs to build complex software. This one makes code insecure by default. API is the willful disregard of simple, established security designs.

    First, we must step back into history to establish a departure point for ignorance. This is just one of many. Almost seven years ago on July 13, 2004 PHP 5.0.0 was officially released. Importantly, it included this note:

    A new MySQL extension named MySQLi for developers using MySQL 4.1 and later. This new extension includes an object-oriented interface in addition to a traditional interface; as well as support for many of MySQL’s new features, such as prepared statements.

    Of course, any new feature can be expected to have bugs and implementation issues. Even with an assumption that serious bugs would take a year to be worked out, that means PHP has had a secure database query mechanism for the past six years.1

    The first OWASP Top 10 list from 2004 mentioned prepared statements as a countermeasure.2 Along with PHP and MySQL, .NET and Java supported these, as did Perl (before its popularity was subsumed by buzzword-building Python and Ruby On Rails). In fact, PHP and MySQL trailed other languages and databases in their support for prepared statements.

    SQL injection itself predates the first OWASP Top 10 list by several years. One of the first summations of the general class of injection attacks was the 1999 Phrack article, Perl CGI problems. SQL injection was simply a specialization of these problems to database queries.

    So, we’ve established the age of injection attacks at over a dozen years old and reliable countermeasures at least six years old. These are geologic timescales for the Internet.

    There’s no excuse for SQL injection vulnerabilities to exist in 2011.

    It’s not a forgivable coding mistake anymore. Coding mistakes most often imply implementation errors – bugs due to typos, forgetfulness, or syntax. Modern SQL injection vulns are a sign of bad design. For six years, prepared statements have offered a means of establishing a fundamentally secure design for database queries. It takes actual effort to make them insecure. SQL injection attacks could still happen against a prepared statement, but only due to egregiously poor code that shouldn’t pass a basic review. (Yes, yes, stored procedures can be broken, too. String concatenation happens all over the place. Never the less, writing an insecure stored procedure or prepared statement should be more difficult than writing an insecure raw SQL statement.)

    Maybe one of the two billion PHP hobby projects on Sourceforge could be expected to still have these vulns, but not real web sites. And, please, never in sites for security firms. Let’s review the previous few months:

    The list may seem meager, but there’s an abundane of sites that have had SQL injection vulns. We just don’t have a crowdsourced equivalent for it like xssed.org tracks cross-site scripting.

    XSS is a little more forgivable, though no less embarrassing. HTML injection flaws continue to plague sites because of implementation bugs. There’s no equivalent of the prepared statement for building HTML or HTML snippets. This is why the vuln remains so pervasive: No one has figured out the secure, reliable, and fast way to build HTML with user-supplied data. This doesn’t imply that attempting to do so is a hopeless cause. On the contrary, JavaScript libraries can reduce these problems significantly.

    For all the articles, lists, and books published on SQL injection one must assume that developers are being persistently ignorant of security concepts to such a degree that five years from now we may hear yet again of a database hack that disclosed unencrypted passwords.

    If you’re going to use performance as an excuse for avoiding prepared statements then you either haven’t bothered to measure the impact, you haven’t understood how to scale web architectures, and you might as well turn off HTTPS for the login page so you can get more users logging in per second. If you have other excuses for avoiding database security, ask yourself if it takes longer to write a ranting rebuttal or a wrapper for secure database queries.

    There may in fact be hope for the future. The rush to scaleability and the pious invocation of “cloud” has created a new beast of NoSQL datastores. These NoSQL datastores typically just have key-value pairs with grammars that aren’t so easily corrupted by a stray apostrophe or semi-colon in the way that traditional SQL can be corrupted. Who knows, maybe security conferences will finally do away with presentations on yet another SQL injection exploit and find someone with a novel, new NoSQL Injection vulnerability.

    Advanced Persistent Ignorance isn’t limited to SQL injection vulnerabilities. It has just spectacularly manifested itself in them. There are many unsolved problems in information security, but there are also many mostly-solved problems. Big unsolved problems in web security are password resets (overwhelmingly relying on email) and using static credit card numbers to purchase items.

    SQL injection countermeasures are an example of a mostly-solved problem. Using prepared statements isn’t 100% secure, but it makes a significant improvement. User authentication and password storage is another area of web security rife with errors. Adopting a solution like OpenID can reduce the burden of security around authentication. As with all things crypto-related, using well-maintained libraries and system calls are far superior to writing your own hash function or encryption scheme.

    Excuses that prioritize security last in a web site design miss the point that not all security has to be hard. Nor does it have to impede usability or speed of development. Crypto and JavaScript libraries provide high-quality code primitives to build sites. Simple education about current development practices goes just as far. Sometimes the state of the art is actually several years old – because it’s been proven to work.

    The antidote to API is the continuous acquisition of knowledge and experience. Have some cake.

    1. MySQL introduced support for prepared statements in version 4.1, which was first released April 3, 2003. 

    2. https://www.owasp.org/index.php/A6_2004_Injection_Flaws 

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