Simon Willison’s Weblog

314 items tagged “security”

TL;DR on the KRACK WPA2 stuff—you can repeatedly resend the 3rd packet in a WPA2 handshake and it’ll reset the key state, which leads to nonce reuse, which leads to trivial decryption with known plaintext. Can be easily leveraged to dump TCP SYN traffic and hijack connections.

Graham Sutherland # 16th October 2017, 2:14 pm

Exploding Git Repositories. Kate Murphy describes how git is vulnerable to a similar attack to the XML “billion laughs” recursive entity expansion attack—you can create a tiny git repository that acts as a “git bomb”, expanding 12 root objects to over a billion files using recursive blob references. # 12th October 2017, 7:43 pm

The Absurdly Underestimated Dangers of CSV Injection. This is horrifying. A plain old CSV file intended for import into Excel can embed formulas (a value prefixed with an equals symbol) which can execute system commands—with a big honking security prompt that most people will likely ignore. Even worse: they can embed IMPORTXML() functions that can silently leak data from the rest of the sheet to an external URL—and those will work against Google Sheets as well as Excel. # 10th October 2017, 4:13 am

Is there anyway to game unique link verifications?  Like when you get sent a link of the form https:/ How would one change the digits to reproduce another working link?

Not if they’ve been implemented correctly.

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How could GitHub improve the password security of its users?

By doing exactly what they’re doing already: adding more sophisticated rate limiting, and preventing users from using common weak passwords.

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What steps can I take to protect my data in case my laptop gets stolen?

Set up full drive encryption—that way if someone steals your laptop they won’t be able to access your data without a password.

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What Javascript tools are there for cleansing input?

Don’t cleanse. Escape instead.

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I would like to setup a web-server which will be used solely by myself. What would be the safest way to do so in terms of confidentiality of the contents?

I haven’t configured them myself, but it might be worth looking in to client SSL certificates for this. That way your server won’t communicate with any browser that hasn’t installed a certificate which you generate. I believe the BBC used to use this for a lot of their important servers which they wanted to be accessible only by their own developers from across the internet (I don’t know if they still do).

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What are the best practices to avoid XSS and SQL Injections attacks (platform agnostic)?

Input validation is, in my opinion, a red herring. Sure—if you ask the user for an integer or date you should make sure they entered one before attempting to save it anywhere or use it for processing, but injection attacks often involve text fields (e.g. names, or comments posted on Quora) and validating those on input is a recipe for banning “Tim O’Reilly” from ever creating a proper profile on your site!

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CSRF: Flash + 307 redirect = Game Over. Here’s the exploit that Django and Rails both just released fixes for. It’s actually a flaw in the Flash player. Flash isn’t meant to be able to make cross-domain HTTP requests with custom HTTP headers unless the crossdomain.xml file on the other domain allows them to, but it turns out a 307 redirect (like a 302, but allows POST data to be forwarded) confuses the Flash player in to not checking the crossdomain.xml on the host it is being redirect to. # 10th February 2011, 10:07 pm

The code injected to steal passwords in Tunisia. Here’s the JavaScript that (presumably) the Tunisian government were injecting in to login pages that were served over HTTP. # 24th January 2011, 6:45 pm

National politics of snoopiness vs corporate ethic of not being evil aren’t directly compatible, and the solution here only works because (let’s face it) Tunisia is not a rising economic force. If you’re selling ads in China, you don’t get to pretend that the Great Firewall of China is a security issue.

Nat Torkington # 24th January 2011, 6:11 pm

The Inside Story of How Facebook Responded to Tunisian Hacks (via) “By January 5, it was clear that an entire country’s worth of passwords were in the process of being stolen right in the midst of the greatest political upheaval in two decades.”—which is why you shouldn’t serve your login form over HTTP even though it POSTs over HTTPS. # 24th January 2011, 6:06 pm

Why would someone browse the web with JavaScript disabled?

Security conscious users (who understand the implications of XSS and CSRF attacks) sometimes disable JavaScript completely, or use a tool like the NoScript extension to disable it for all sites and only re-enable it on a small whitelist of sites that they trust.

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What are the JSON security concerns in web development?

Be very careful when implementing JSON-P for authenticated actions—evil third party sites could assemble URLs to your user’s private data and steal it. This attack has worked against Gmail in the past.

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Why do browsers allow cross-domain JavaScript to execute but not XMLHttpRequests?

It’s called the Same Origin Policy, and it’s principally about intranets. Imagine you have a URL http://intranet.corp/top-secret-...—and you then visit . If cross domain XHR was allowed the evil site could suck that secret document off your intranet without you realising.

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Bleach, HTML sanitizer and auto-linker. HTML sanitisation is notoriously difficult to do correctly, but Bleach (a Python library) looks like an excellent effort. It uses the html5lib parsing library to deal with potentially malformed HTML, uses a whitelist rather than a blacklist and has a neat feature for auto-linking URLs that is aware of the DOM (so it won’t try to auto-link a URL that is already wrapped in a link element). It was written by the Mozilla team for and so it should be production ready. # 25th October 2010, 1:32 pm

Firesheep (via) Oh wow. A Firefox extension that makes sniffing for insecured (non-HTTPS) cookie requests on your current WiFi network and logging in as that person a case of clicking a couple of buttons. Always possible of course, but it’s never been made easy before. Private VPNs are about to become a lot more popular. # 25th October 2010, 9:11 am

Why do some websites implement their logout link as a form post via JavaScript versus a plain old GET request?

Probably because if you implement logout as a GET action, I can force you to log out of a site by tricking you in to visiting a page with an <img src="" width="1" height="1"> element on it.

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Schneier on Stuxnet. Stuxnet now rivals Wikileaks as the real life plot most likely to have leaked from science fiction. # 9th October 2010, 10:57 am

Why are XSS attacks spreading like fire these days?

XSS attacks are common and easy, and crop up all the time. What’s new is that the number of people who are aware of the potential for XSS worms has increased hugely, so when an XSS does crop up in something popular there’s a much higher chance of someone turning it in to a worm (as happened with Twitter the other day).

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In what circumstances should one use “magic quotes” in PHP?

Absolutely never. Magic quotes was a badly designed feature, and PHP has been trying to escape its legacy for years. If you are constructing SQL strings using string concatenation you’re asking for trouble—use prepared statements or a library that interpolates and correctly escapes variables for you.

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Why do some people disable JavaScript in their browser?

For security reasons.

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Jeremiah Grossman: I know who your name, where you work, and live. Appalling unfixed vulnerability in Safari 4 and 5 —if you have the “AutoFill web forms using info from my Address Book card” feature enabled (it’s on by default) malicious JavaScript on any site can steal your name, company, state and e-mail address—and would be able to get your phone number too if there wasn’t a bug involving strings that start with a number. The temporary fix is to disable that preference. # 22nd July 2010, 8:44 am

“Likejacking” Takes Off on Facebook. The Facebook Like button is vulnerable to Clickjacking, and is being widely exploited. Since Likes show up in your Facebook stream, it’s an easy attack to make viral. The button is implemented on third party sites as an iframe, which would seem to me to be exploitable by design (just make the iframe transparent in the parent document and trick the user in to clicking in the right place). I can’t think of any way they could support the embedded Like button without being vulnerable to clickjacking, since clickjacking prevention relies on not allowing your UI elements to be embedded in a hostile site while the Like button’s functionality depends on exactly that. # 3rd June 2010, 10:01 am

A New Type of Phishing Attack. Nasty trick from Ava Raskin—detect when your evil phishing page loses focus (when the user switches to another tab, for example), then replace the page content with a phishing UI from a site such as Gmail. When the user switches back they’re much less likely to bother checking the URL. Combine with CSS history sniffing to only show a UI for a site that you know the user has visited. Combine that with timing tricks to only attack sites which the user is currently logged in to. # 25th May 2010, 3:20 pm

OpenCart CSRF Vulnerability. Avoid OpenCart—it’s vulnerable to CSRF, but the maintainer has no intention of fixing it as “there is no way that I’m responsible for a client being stupid enough to click links in emails”. # 25th May 2010, 12 am

Busting frame busting: a study of clickjacking vulnerabilities at popular sites (via) Fascinating and highly readable security paper from the Stanford Web Security Research group. Clickjacking can be mitigated using framebusting techniques, but it turns out that almost all of those techniques can be broken in various ways. Fun examples include double-nesting iframes so that the framebusting script overwrites the top-level frame rather than the whole window, and a devious attack against the IE and Chrome XSS filters which tricks them in to deleting the framebusting JavaScript by reflecting portions of it in the framed page’s URL. The authors suggest a new framebusting snippet that should be more effective, but sadly it relies on blanking out the whole page in CSS and making it visible again in JavaScript, making it inaccessible to browsers with JavaScript disabled. # 24th May 2010, 11:40 am

The answers to your Security Questions are case sensitive and cannot contain special characters like an apostrophe, or the words “insert,” “delete,” “drop,” “update,” “null,” or “select.”

Sacramento Credit Union # 14th May 2010, 12:40 am incident report for 04/09/2010. An issue was posted to the Apache JIRA containing an XSS attack (disguised using TinyURL), which stole the user’s session cookie. Several admin users clicked the link, so JIRA admin credentials were compromised. The attackers then changed the JIRA attachment upload path setting to point to an executable directory, and uploaded JSPs that gave them backdoor access to the file system. They modified JIRA to collect entered passwords, then sent password reset e-mails to team members and captured the new passwords that they set through the online form. One of those passwords happened to be the same as the user’s shell account with sudo access, leading to a full root compromise of the machine. # 14th April 2010, 9:08 am